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Punjab State Board PSEB 10th Class Science Important Questions Chapter 5 Periodic Classification of Elements Important Questions and Answers.

PSEB 10th Class Science Important Questions Chapter 5 Periodic Classification of Elements

Long Answer Type Questions

Question 1.
What do you understand by Dobereiner’s triads? Give some examples to support it.
Answer:
In 1817, a German Chemist, Dobereiner, gave a classification in which the similar elements were arranged in groups of three called Triads. The arrangement was such that the atomic mass of the middle element was almost the average of the atomic masses of the first and third elements. For example, if A, B and C are the elements present in the triad, then

Atomic mass of B =\(\frac{\text { Atomic mass of } \mathrm{A}+\text { Atomic mass of } \mathrm{C}}{2}\)

Examples of triads.
A few examples of triads are listed as given ahead :
1. Lithium, Sodium. Potassium
Atomic mass of Lithium (Li) = 7
Atomic mass of Potassium (K) = 39
Atomic mass of Sodium (Na) = \(\frac{39+7}{2}\) = 23
Actual atomic mass of sodium = 23

This group of triads is called Alkali Metal Group. All the elements present are metals, have valency equal to one (1) and dissolve in water to form soluble hydroxides called alkalis.

2. Calcium, Strontium, Barium
Atomic mass of Calcium (Ca) = 40
Atomic mass of Barium (Ba) = 137
Atomic mass of Strontium (Sr) = \(\frac{137+40}{2}=\frac{177}{2}\) = 88.5
Actual atomic mass of strontium = 88

This group of triads is called Alkaline Earth Metals Group. All the elements present are metals, have valency equal to two (2) and their oxides dissolve in water to form hydroxides which are alkaline in nature.

Question 2.
(a) What was Dobereiner’s basis of classifying elements?
Answer:
Dobereiner gave a classification in which the elements were arranged in a group of three elements called triads. The arrangement was such that the atomic masses of the middle elements were almost the average of the atomic masses of the first and third elements.

(b) What is the basis of classification of elements according to Mendeleev?
Answer:
The major contribution in the classification of the elements is by Mendeleev, a Russian chemist. He studied in detail the properties of the elements and made a very important observation. He stated that when elements are arranged in order of increasing atomic masses, the elements with similar properties recur after a definite gap. He based his classification of law called Mendeleev’s Periodic Law. The law may be stated as:

Physical and chemical properties of the elements are periodic function of their atomic weights or atomic masses.

Question 3.
Give a brief discussion of the Mendeleev’s classification of the elements.
Answer:
Mendeleev’s classification of the elements is based upon the Mendeleev’s periodic law. The law helped him to develop a table called Mendeleev’s Periodic Table. The table has been divided into vertical columns which are called Groups and horizontal rows which are known as Periods.

These are briefly discussed as follows :
1. Groups: These are the vertical rows. There are in all eight groups. The elements present in first seven groups are called Normal Elements. The elements present in group VIII are called the Transition Elements. Each group (I to VII) has been further divided into sub-groups which are called A and B. The inert gas or noble gas elements (He, Ne, Ar, Kr, Xe) were not known at that time. Therefore, they were not shown in the table. All the elements placed in a group have the same valency. Ail the elements present in a sub-group have the similar properties. For example, group I-B includes element Cu (Copper), Ag (Silver) and Au (Gold). They have similar properties.

2. Periods: In the periodic table horizontal rows are called periods. There were in all six periods in the original periodic table. The seventh period was added later on and this is not shown in the periodic table. The properties of the elements present in a period change systematically. For example, in every period, the first element is a typical metal. As we move from left to right, the metallic character gradually decreases and non- metallic character increases. For example, in period 2, the first element Li (Lithium) is a metal while the last element F (Fluorine) is a non-metal. The Mendeleev’s Periodic Table is shown below :

Mendeleev’S Periodic Table

Question 4.
(a) Why do we classify elements?
Answer:
To simplify and systematize the study of known elements.

(b) What were the two criteria used by Mendeleev in creating his Periodic Table?
Answer:

1. Mendeleev arranged the elements in order of increasing atomic masses.
2. Mendeleev considered the compounds formed by the elements oxygen and hydrogen.

(c) Why did Mendeleev leave some gaps in his Periodic Table?
Answer:
For the discovery of new elements.

(d) In Mendeleev’s Periodic Table, why was there no mention of Noble gases like7 Helium, Neon and Argon?
Answer:
Because noble gases were not known at that time.

(e) Would you place the two isotopes of chlorine, Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because their chemical properties are the same? Justify your answer.
Answer:
In the same slot because Cl-35 and Cl-37 have same chemical properties.

Question 5.
How did Mendeleev’s Periodic Table help in the discovery of new elements?
Answer:
When Mendeleev gave the periodic table, only 63 elements were known. The classification was based on two major properties :

• Elements are arranged in order of increasing atomic masses.
• Elements present in a group have similar properties.

Many elements were not known at the time the periodic table was given. Therefore, Mendeleev left gaps for these elements in the periodic table. But the properties of these elements could be predicted. For example, let us suppose that Rb (Rubidium) a member of group IA was not known when Mendeleev framed the periodic table. But its properties could be predicted. It was expected to be a metal with valency equal to 1. It was expected to be soluble in water to form a soluble hydroxide RbOH which is an alkali. This helped in the discovery of the element. In this manner, a number of elements could be discovered.

Question 6.
Discuss some major merits of the Mendeleev’s Periodic Table.
Answer:
Merits of Mendeleev’s Periodic Table
Mendeleev’s periodic table was the first proper systematic classification of the elements. The important merits of the table are listed as follows :
1. Systematic study of elements. With the classification of elements into groups and periods, their study became quite systematic. For example, if the properties of one particular element in a group are known, those of the other elements could be predicted. Actually, elements placed in a group are expected to show similar characteristics.

2. Correction of wrong atomic masses. The periodic table helped in correcting the atomic masses of some of the elements because the elements were arranged in order of their increasing atomic masses.

3. Prediction of new elements. At the time Mendeleev gave the periodic table, only 63 elements were known. While arranging these elements in groups and periods, certain gaps were left. These gaps represented some undiscovered elements. But the properties of these unknown elements could be predicted from their positions in the respective groups. This helped, later on, to discover these elements.

Question 7.
On the basis of Mendeleev’s Periodic Table given following, answer the questions that follow the table :

(a) Name the element which is in
(i) 1st group and 3rd period
Answer:
Sodium

(ii) VII group and 2nd period.
Answer:
Fluorine

(b) Suggest the formula for the following :
(i) oxide of nitrogen
Answer:
N₂O₅

(ii) hydride of oxygen.
Answer:
H₂O.

(c) In group VIII of the Periodic Table, why does cobalt with atomic mass 58.93 appear before nickel having atomic mass 58.71?
Answer:
Because the elements with similar properties could be grouped together.

(d) Besides gallium, which two other elements have since been discovered for which Mendeleev had left gaps in his Periodic Table?
Answer:
Scandium and Germanium.

(e) Using atomic masses of Li, Na and K, find the average atomic mass of Li and K and compare it with the atomic mass of Na. State the conclusion drawn from this activity.
Answer:
Average atomic mass of Li and K = \(\frac{6.939+39.102}{2}=\frac{46.04}{2}\) = 23.02
Atomic mass of Na = 22.99
Hence Atomic mass of Na = Average of atomic masses of Li and K = \(\frac{46.04}{2}\) = 23.02

Question 8.
Point out the major defects in Mendeleev’s Periodic Table.
Answer:
Defects in Mendeleev’s Periodic Table:
Mendeleev’s periodic table was quite helpful in the classification of the elements.

But it had certain defects also. These are discussed as follows :
1. Position of hydrogen. Hydrogen was placed at the top of group LA. It is a non-metal where all other elements included in the group are metals.

2. Position of isotopes. The periodic table is based on the basis of the atomic masses of the elements and the elements with different atomic masses must be given separate places in the table. If this is correct, all the isotopes of an element must be allotted separate positions. For example, there are three isotopes for hydrogen and they must be given three separate places in the table. But only one position for hydrogen has been given.

3. Wrong order of atomic masses of some elements. In the table, the elements are arranged in order of increasing atomic masses. This means that the element with higher atomic mass must be placed after the element with the lower atomic mass. But in the table, there are some anomalies. For example, Co (Cobalt) with atomic mass 58-9 should be placed after Ni (Nickel) with atomic mass 58-7. But it has been placed before nickel.

4. Elements with similar properties placed in different groups. In the periodic table, it has been found that the elements with similar properties are placed in different groups. For example, copper and mercury have many common properties. But copper has been placed in group I B and mercury in group II B.

5. No similarity in the elements placed in sub-groups. The elements present in different sub-groups of the same group are expected to have common properties. But these are quite different. For example, elements in group I A are very soft and reactive metals but elements in group IB are hard and less reactive in nature.

6. No explanation for the cause of periodicity. Mendeleev was not in a position to explain why the elements included in a group show similar properties.

Question 9.
Give a brief description of Long Form of Periodic Table.
Answer:
The Long form of periodic table has been formed by arranging the elements in order of increasing atomic numbers. It is based upon Modern periodic law which states that the properties of the elements are the periodic function of their atomic numbers. Just as in case of the Mendeleev’s table, this periodic table has also been divided into Periods and Groups.
(A) Groups
These are the vertical columns. In all, there are eighteen groups in the table. The details of the groups are as follows :

Long Form of Periodic Table of Modern Periodic Table

• Group 1: The elements present in group I or 1 are called Alkali Metals.
• Group 2: The elements which are present in group IIA or 2 are called Alkaline Earth Metals.
• Groups 13 to Group 18: There are in all six groups. The Groups 13 to 16 are named after the first element present in the family. For example, Group IIIA or 13 is called Boron Family because first member is boron.
• Group 17 consists of a family called Halogen Family.
• The group 18 is also called zero group because the elements have zero valency. These elements are ail gases. They have very little tendency to take part in chemical combination. These are also called Noble Gases.

In the latest Long Form of Periodic Table, groups of Alkali metals and Alkaline erttH metals are given numbers 1 and 2. The transition of elements are numbered from its,2 The non-metals are included in groups 13 to 18.

Group No.	Name of Family
Group 13	Boron Family
Group 14	Carbon Family
Group 15	Nitrogen Family
Group 16	Oxygen Family
Group 17	Halogens
Group 18 or zero group	Noble Gases

• Group 3 to Group 12: There are in all ten groups. These are all metals and are called Transition elements. When we go down each group, the metallic character further increases.
• Group 3: Group 3 also includes fourteen elements belonging to Lanthanide family. These are called Lanthanides because they start after Lanthanum (La) with Z = 57. These are present in the 6th period as shown in the table.
• It also includes another fourteen elements called Actinides. These are present in 7th period. These are so called as they come after Actinium (Ac) with Z = 89. These are placed at the bottom of the table for convenience.

(B) Periods
Periods are the horizontal rows which are present in the Long Form of Periodic Table. Different periods have different number of elements and their atomic numbers are continuous. There are in all seven periods. The seventh period is still incomplete. The number of elements which are included in each period are given below :

Period	No. of elements	Name of the Period
1	2	Shortest Period
2	8	Short Period
3	8	Short Period
4	18	Long Period
5	18	Long Period
6	32	Longest Period
7	20	Incomplete Period

Question 10.
What is periodicity? What is the cause of periodicity?
Answer:
Periodicity may be defined as the repetition of the similar properties of the elements placed in a group and separated by definite gaps of atomic numbers (8, 8, 18, 18, 32).

Cause of Periodicity. The properties of the elements, particularly the chemical properties, are linked with number of electrons present in the outermost shell of their atoms which is also called Valence shell. Elements with similar valence shell electronic configurations are expected to have similar properties.

It may be noted that all the elements which are present in a group have the same number of electrons in the valence shells of their atoms. In other words, the same valence shell electronic arrangement gets repeated after definite gaps of atomic numbers (8, 8, 18, 18, 32). Therefore, the elements placed in a group show similar properties.

Example, Let us write the electronic distribution of the first four members of the alkali metals present in group I.

All the four elements have one electron each in the valence shell of their atoms. They have, therefore, similar properties.

Question 11.
(a) What were the two major shortcomings of Mendeleev’s periodic table? How have these been removed in the modern periodic table?
Answer:
The shortcomings of Mendeleev’s periodic table are :

• Isotopes of an element find different positions in periodic table.
• Some chemically similar elements have been separated and some dissimilar elements are placed together.

In these Modern Periodic Table
Modern Table

• Isotopes of an element occupy the same position because they have same atomic number.
• The similar elements are grouped together and dissimilar elements are separated.

(b) Two elements X and Y have atomic numbers 12 and 16 respectively. Write the electronic configuration for these elements. To which period of the modern periodic table do these two elements belong? What type of bond will be formed between them and why?
Answer:

Element	Electronic Configuration	Period
X12	2, 8, 2	3rd
Y16	2, 8, 6	3rd

They will form ionic bonds because two electrons are transferred from X to Y so that they get their octets complete :

Question 12.
Why is Long Form of Periodic Table regarded better than Mendeleev’s Periodic Table?
Or
How could Modern Periodic Table remove various anomalies of Mendeleev’s Periodic Table?
Answer:
Long Form of Periodic Table is regarded better than the Mendeleev’s periodic table due to the following reasons:

• It is based upon atomic number which is considered better than the atomic mass because the properties of the elements are related to the atomic number.
• It explains why the elements placed in a group show similar properties but Mendeleev’s Periodic Table gives no explanation for the same.
• All groups in the Periodic Table are independent groups and there are no sub¬groups as in Mendeleev’s Periodic Table.
• Many defects in the Mendeleev’s Periodic Table have been removed.
• There is no confusion regarding the position of isotopes because all the isotopes of an element have the same atomic number.
• The periodic table is more systematic than the Mendeleev’s table and is easy to remember.

Question 13.
The following tables shows the position of six elements A, B, C, D, E and F in the periodic table.

Using the above table answer the following questions :
(a) Which element will form only covalent compounds?
Answer:
E

(b) Which element is a metal with valency 2?
Answer:
D

(c) Which element is non-metal with valency of 3?
Answer:
B

(d) Out of D and E, which one has a bigger atomic radius and why?
Answer:
D

(e) Write a common name for the family of elements C and F,
Answer:
The noble gases.

Question 14.
The question refers to the elements of the periodic table with atomic number from 3 to 18.

(a) Which of these :
(i) is/are noble gas?
Answer:
H, P

(ii) is it a halogen?
Answer:
G, O

(iii) is an alkali metal?
Answer:
A, I

(iv) is it a metal with valency 2?
Answer:
A, I

(b) Write the electronic arrangement of G.
Answer:
G has the electronic configuration = 2, 7

(c) If A combines with F, what would be the formula of resulting compound?
Answer:

Short Answer Type Questions

Question 1.
Atomic number is considered to be a more appropriate parameter than atomic mass classification of elements in a periodic table. Why?
How does atomic size of elements vary on moving from
(i) Left to right in a period.
(ii) from top to bottom in a group.
Give reasons for your answers.
Answer:

• This is because atomic number is a more fundamental property of an atom.
• As we move from left to right along a period atomic radius decreases due to increase in effective nuclear charge.
• As we move from top to bottom in a group, atomic radius increases. This is due to addition of new electronic shells.

Question 2.
Define periodic law. Why was it necessary to change the basis of classification from atomic masses to atomic numbers?
Answer:
Periodic Law: The properties of elements are a periodic function of their atomic numbers. It was necessary to change the basis of classification from atomic masses to atomic numbers because atomic number and not atomic mass is the fundamental property of an element.

Question 3.
What do you understand by the term periodicity? Do the properties of two elements placed in a group the same? Illustrate.
Answer:
The repetition of the similar properties of the elements placed in a group and separated by definite gaps of atomic numbers (8, 8, 18, 18, 32) is called periodicity. The elements placed in a group show similar properties, e.g. consider group 1 elements.

Element	Symbol	Electronic configuration
Lithium	(3)	Li – 2, 1
Sodium	(11)	Na – 2, 8, 1
Potassium	(19)	K – 2, 8, 8, 1
Rubidium	(37)	Rb – 2, 8, 18, 8, 1
Cesium	(55)	Cs – 2, 8, 18, 18, 1
Francium	(87)	Fr – 2, 8, 18, 32, 18, 8, 1

These elements show similar properties because they have similar outer electronic configurations.

Question 4.
What was wrong with Dobereiner’s classification of elements?
Answer:
Dobereiner classified the elements in group of three in such a way that the atomic mass of the middle element was the mean of the first and the third elements. But he could not find many triads of elements. Therefore, the classification was rejected.

Question 5.
What properties do ail elements in the same column of the periodic table as boron have in common?
Answer:
The elements of Boron family in the periodic table show

• Tricovalency
• Form trihalides
• Form trioxides
• React with halogens to form halides.

Question 6.
Indicate the atomic number of elements of period 3 of Modern periodic table :
(a) non-metals
Answer:
14, 15, 16, 17

(b) elements forming negative ions.
Answer:
15, 16, 17

(c) elements with high melting points.
Answer:
11, 12, 13, 14

(d) elements forming positive ions.
Mention the atomic number only.
Answer:
11, 12, 13

Question 7.
Define atomic radius. Give its units.
Answer:
Atomic radius. It may be defined as the distance between the centre of nucleus and the outermost shell of an isolated atom.

Also the atomic radius of a non-metallic element is defined as half the distance between the nuclei of two atoms bound by a single covalent bond.
Units = Å or pm (picometre)
e.g. atomic radius of hydrogen atom = 37 pm.

Question 8.
How does atomic radius vary down a group and along a period?
Answer:
Variation in a group. The atomic radius generally increases from top to bottom in a group due to the addition of a new shell.
Variation along a period. The atomic radius decreases on moving from left to right due to the increase in nuclear charge.

Question 9.
Write down the electronic configuration of elements with atomic numbers 2, 14, 17, 19. Indicate the group of the periodic table to which they belong.
Answer:
The information is being given in a tabular form.

Atomic number	Electronic configuration K L M N	Group
2	2	18
14	2, 8, 4	14
17	2, 8, 7	17
19	2, 8, 8, 1	1

Question 10.
Locate the following group in the periodic table :
(a) Alkali metals
Answer:
Alkali metals: Group 1 or IA

(b) Halogens
Answer:
Halogens: Group 17 or VIIA

(c) Alkaline earth metals
Answer:
Alkaline earth metals: Group 2 or IIA

(d) Noble gases.
Answer:
Noble gases: Group 18 or zero

Question 11.
What properties do the elements in the same vertical column of the periodic table as fluorine have in common?
Answer:
These are :

• They form diatomic molecules F₂, Cl₂, Br₂ I₂
• They are non-metals.
• They show a valency of one.

Question 12.
Write the chemical electronic configuration of nitrogen (N = 7) and phosphorous (P = 15).
Answer:

Question 13.
(i) Name the members of the alkaline earth family.
Answer:
The members of the alkaline earth family are :
Be, Mg, Ca, Sr, Ba, Ra.

(ii) To which group do they belong?
Answer:
They belong to group 2.

(iii) Which member is radioactive in nature?
Answer:
The radioactive member in them is Radium (Ra).

(iv) Which member is the least reactive?
Answer:
The least reactive member of the family is Beryllium (Be).

Question 14.
Why are the members of group 1 called alkali metals?
Answer:
The members of group 1 are called alkali metals because all of them are water soluble. They react with water to form soluble hydroxides. The soluble hydroxides of the metals are called alkalies.

Question 15.
An atom has the electronic configuration 2, 8, 7.
(a) What is the atomic number of this element?
Answer:
The atomic number of the element = Total number of electrons
= 2 + 8 + 7 = 17

(b) To which of the following elements would it be chemically similar? (atomic numbers are given) N (7), F (9), P (15), Ar (18).
Answer:
The electronic configurations of given atom and N, F, P and Ar are.

Atom	Electronic configuration
	K	L	M
	2	8	7
N	2	5
F	2	7
P	2	8	5
Ar	2	8	8

Since F has same number of electrons in the outermost shell as the given atom. Hence, the given atom is chemically similar to F.

Question 16.
What physical and chemical properties of elements were used by Mendeleev in creating his periodic table? List two observations which posed a challenge to Mendeleev’s Periodic Law.
Answer:
He selected the compounds of the elements with oxygen and hydrogen. He gave a table based upon atomic weights of the elements.

Limitations of Mendeleev’s Classification

• The position of hydrogen was uncertain.
• The isotopes of elements were not given proper positions in the periodic table.

Question 17.
(a) What are amphoteric oxides? Choose the amphoteric oxides from amongst the following oxides :
Na₂O, ZnO, Al₂O₃, CO₂, HaO
Answer:
The oxides which can react both with acids as well as bases to produce salts and water.

(b) Why is it that non-metals do not displace hydrogen from dilute acids?
Answer:
This is because non-metals cannot lose electrons and cannot reduce H⁺ ions from acid to H₂.

Question 18.
What are noble gas elements? Why are they so called?
Answer:
Noble gas elements are the. elemehts present in group 18 of the periodic table which is also called zero group, It means that the valency of the elements is zero. Actually, whereas the first member helium has two electrons in its only shell, the atoms of the remaining elements (Neon, Argon, Krypton, Xenon and Radon) have eight electrons in their outermost shells. They do not have any tendency to combine with atoms of other elements. Hence, they show zero valency. These are also called noble gases because they do not take part in chemical combination.

Question 19.
How is metallic character of an element defined? How does the metallic character of the elements change in a group?
Answer:
The metallic character of an element may be expressed in terms of its tendency to lose electrons and to form positive ion.
M (Element) → M⁺ + e^–

In a group the metallic character increases’ downwards. For example, among the elements of group 2, Beryllium (Be) is the least metallic. At the same time, radium (Ra) which is the last element is maximum metallic in nature.

Question 20.
Why do the elements present in a group show similar chemical properties?
Answer:
The properties of the elements, particularly the chemical properties are related to valence shell electronic distribution. The elements with the same valence shell electronic distribution have the similar chemical properties. For example, the members, of alkaline earth metal family (Group 2) have two electrons in the valence shell of their atoms. They therefore, show similar chemical properties.

Question 21.
How does the reactivity of the metals vary in a group?
Answer:
In a group, containing metals, the reactivity increases down the group. For example, in the metals of group 1 (Alkali metals), Lithium reacts with water very slowly. Sodium is more reactive and potassium is. still more reactive than sodium.

Question 22.
Name the elements present in the second period. Give their electronic configuration.
Answer:
The second period of the Long Form of Periodic Table has eight elements. The first element is Lithium and the last element is Neon. The electronic configuration of the elements are given below:

Question 23.
Why do not the elements present in a period show same valency?
Answer:
The valency of the element is related to the number of electrons in the outermost energy shell of its atom. Since the elements present in a period have different number of valence electrons or outermost electrons, they show different valencies.

Question 24.
The metallic character of the elements in a period decreases from left to the right. Justify.
Answer:
In every period, as we move from left to right, the metallic character of the elements decreases gradually. This is shown with the elements present in the third period.

Question 25.
Give symbols for :
(a) a metal belonging to second group of the periodic table.
Answer:
The metal belonging to second group is calcium (Ca).

(b) a metal belonging to the third group of the periodic table.
Answer:
The metal belonging to third group is aluminium (Al).

(c) two non-metals belonging to the halogen family.
Answer:
The two non-metals of halogen family are fluorine (F) and chlorine (Cl).

Question 26.
Write electronic structures of:
(i) Potassium
(ii) Lithium
(iii) Fluorine.
Answer:
The electronic configurations of the atoms are given below :

Question 27.
Name two other elements which are in the same family as
(i) carbon
Answer:
Carbon belongs to the group 16. Two other elements are silicon (Si) and germanium (Ge).

(ii) fluorine
Answer:
Fluorine belongs to group 17. Two other elements are chlorine (Cl) and bromine (Br).

(iii) sodium.
Answer:
Sodium belongs to group 1. Two other elements are lithium (Li) and potassium (K).

Question 28.
Carbon (atomic number 6) and silicon (atomic number 14) are elements in the same group of the periodic table. Give the electronic arrangements of the carbon and silicon atoms and state the groups in which these elements occur.
Answer:
The required information may be given in a tabular form as follows :

Element	Atomic no.	Electronic arrangement	Group
Carbon (C)	6	2, 4	14
Silicon (Si)	14	2, 8, 4	14

Question 29.
Sodium and aluminium have atomic numbers of 11 and 13 respectively. They are separated by one element in the periodic table and have valencies of 1 and 3 respectively. Chlorine and potassium are also separated by one element in the periodic table (their atomic numbers are 17 and 19 respectively) and yet both have valency of one. Explain your answer.
Answer:
Sodium and aluminium: The electronic configurations of the elements are given below :
Sodium (Na) = 2, 8, 1
Aluminium (Al) = 2, 8, 3

The valency in this case is given by the number of valence electrons. Therefore, the valency of sodium is 1 and that of aluminium is 3.

Chlorine and potassium: The electronic configurations of the elements are given below :
Chlorine (Cl) = 2, 8, 7
Potassium (K) = 2, 8, 1

Question 30.
Give the atomic number and electronic distribution of:
(i) The third alkali metal
Answer:
Potassium (19) 2, 8, 8, 1

(ii) The second alkaline earth metal
Answer:
Magnesium (12) 2, 8, 2

(iii) The first halogen
Answer:
Fluorine (9) 2, 7

(iv) The second noble gas.
Answer:
Neon (10) 2, 8.

Question 31.
Observe the following elements in the Modern Periodic Table.

Name the elements A, B, C and D. Also indicate noble gas
Answer:
(A) Lithium
(B) Chlorine
(C) Neon
(D) Potassium C is a noble gas

Question 32.
Match the following :

(a) Fluorine	(i) Metalloid
(b) Neon	(ii) Halogen
(c) Sodium	(iii) Noble gas
(d) Arsenic	(iv) Alkali metal

Answer:

(a) Fluorine	(ii) Halogen
(b) Neon	(iii) Noble gas
(c) Sodium	(iv) Alkali metal
(d) Arsenic	(i) Metalloid

Question 33.
How many electrons can be present in the valence shells of metal atoms and non-metal atoms?
Answer:
Metal atoms have 1, 2 or 3 electrons in their valence shells whereas non-metal atoms have 4 to 7 electrons in their valence shells.

Question 34.
How are the various groups of the Modern Periodic Table designated according to the IUPAC system and old system?
Answer:
The designations of various groups of the Modern periodic table are :

Question 35.
What are the uses of Modern Periodic Table?
Answer:

• Systematic study of the elements. In the periodic table, the elements with similar properties are placed together in the same group. If we know the properties of one element of the group, the properties of other elements belonging to the same group can be predicted. Thus, there is no need to study the properties of all the elements.
• Properties of an element can be predicted from the position of the element in the periodic table. For example, if the element belongs to group IA or IIA it is likely to be a reactive metal, and if it belongs to group VII A it is likely to be a reactive non-metal.
• It has led to the discovery of many new elements.

Very Short Answer Type Questions

Question 1.
How many elements have been discovered so far?
Answer:
114.

Question 2.
How are elements classified?
Answer:
The elements have been classified on the basis of their properties.

Question 3.
Why are group IA elements called alkali metals?
Answer:
This is because all these elements are metals and their oxides and hydroxides give alkaline solutions in water.

Question 4.
What is the basis of Modern Periodic table?
Answer:
It is based upon Modern Periodic law.

Question 5.
Name the family to which halogens belongs?
Answer:
Halogen family.

Question 6.
Name the second elements of group 14.
Answer:
Silicon.

Question 7.
How many valence electrons and present in halogen elements?
Answer:
Seven.

Question 8.
How many elements are present in 4th period?
Answer:
18.

Question 9.
How many electrons are present in Mg²⁺ ion?
Answer:
Ten.

Question 10.
Out of Na and Mg which was larger size?
Answer:
Na

Question 11.
What is the valency of nitrogen?
Answer:
Three.

Question 12.
Out of Na and K which is more reactive?
Answer:
Sodium (Na).

Question 13.
Name the group number of halogen family.
Answer:
Group 17 (or VII-A).

Question 14.
Name the last element of third period?
Answer:
Argon.

Question 15.
What is Dobereiner’s Triad?
Answer:
A group of three elements having similar properties is called Dobereiner’s Triad.

Question 16.
A, B and constitute the Dobereiner s Traid. Atomic mass of A and C are 7 and 23 respectively. Calculate atomic mass of B.
Answer:
\(\frac{7+23}{2}=\frac{30}{2}\) = 15

Question 17.
Name the elements discovered after Mendeleev’s Periodic Table?
Answer:
Scandium (Se), Gallium (Ga), Germanium (Ge) etc.

Question 18.
Name the groups and periods in Mendeleev’s Periodic Table?
Answer:
8 groups and 7 periods.

Question 19.
How does atomic radii as we move from left along a period in the Periodic Table?
Answer:
It decreases.

Question 20.
An element has the electronic configuration 2, 8, 3. What is its group number in Modern Periodic Table?
Answer:
Group 13.

Question 21.
Give the basis of Dobereiner’s classification.
Answer:
Doberenier Triads.

Question 22.
Give the characteristics of Dobereiner’s Triads.
Answer:
The atomic mass of the central element is the average of masses of the other two elements.

Question 23.
What is the drawback of Doberenier’s Triads?
Answer:
All the known elements could be grouped into Triads.

Question 24.
There are three alements A, B and C. The atomic masses of A and C are 7 and 39. What is the atomic mass of B on the bais of Dobereiner’s Traids?
Answer:
Atomic mass of B = \(\frac{7+39}{2}\) = 23.

Question 25.
There are three elements X, Y, Z. Atomic masses of X and Z are 35.5 and 127. What will be atomic mass of Y on the basis of Dobereiner’s Traids?
Answer:
Atomic mass of Y
\(\frac{35.5+127}{2}=\frac{162.5}{2}\) = 81.25

Question 26.
Write Newland’s Law of Octaves for classification of elements.
Answer:
When the elements are arranged in order of increasing atomic masses, eighth elements has properties similar to the first element.

Question 27.
How many element were classified by Newland.
Answer:
Upto mass number 40.

Question 28.
Indicate the group number and period number of P in the modern Periodic Table.
Answer:
Group-15, Period-3.

Question 29.
An element has the electronic configuration 2, 8, 8, 2. Indicate its group and Period in the Modern Periodic Table.
Answer:
Group-12, Period-4.

Question 30.
An element M is in the group 13 of Modern Periodic Table write the formula of its oxide.
Answer:
M₂O₃.

Question 31.
Give the groups and periods in the Modern Periodic Table.
Answer:
Group-18, Periods-7.

Question 32.
Give the electronic configuration of ₁₇Cl³⁵. Also indicate its position in the Periodic Table.
Answer:
Electronic configuation of ₁₇Cl³⁵ = 2, 8, 7
Period number = 3
Group number =17. (VII A)

Question 33.
Give the name and electronic configuation of element with atomic number 9.
Answer:
Fluorine and it has the electronic configuation = 2, 7.

Question 34.
What is Modern Periodic Law?
Answer:
It states that the properties of the elements are the periodic functions of their atomic numbers.

Question 35.
Who gave Newland’s Law of Octaves.
Answer:
Newland.

Question 36.
Define Mendeleev’s periodic law.
Answer:
It states that the properties of the elements are the periodic functions of their atomic masses.

Question 37.
What is the basis of Mendeleev’s Modern Table?
Answer:
It is based upon Mendeleev periodic law and in this table the elements are arranged in order of increasing atomic masses.

Question 38.
How many groups are present in Mendeleev’s Period Table.
Answer:
Eight.

Question 39.
Name the next elements after P in Modern Periodic Table.
Answer:
Sulphur (S).

Question 40.
Give the group number of nitrogen and phosphorus.
Answer:
They belong to group number 15.

Question 41.
Out of Mg and Al which is more metallic?
Answer:
Mg.

Question 42.
Out of Be, Mg, Ca, Al which does not belong to same group?
Answer:
Al.

Question 43.
In which group noble gases are present?
Answer:
Group 18 or group zero.

Question 44.
Na and S are present in the third period of Modern Periodic Table. Which is more metallic and why?
Answer:
Na is more metallic due to larger size than S.

Question 45.
What is metallic character?
Answer:
It is the tendency of an atom of the element to form positive ions by losing electrons.

Question 46.
What is the trend in metallic character on moving from left to right along a period?
Answer:
It decreases.

Multiple Choice Questions:

Question 1.
Who gave Law of octaves?
(A) Newland
(B) Dobereiner
(C) Mendeleef
(D) Lother Mayer.
Answer:
(A) Newland

Question 2.
In Mendeleef’s periodic table which element was discovered in the gap between Boron and Aluminium ?
(A) Na
(B) Ca
(C) Ga
(D) Ba.
Answer:
(C) Ga

Question 3.
According to Mendeleef’s periodic law, the elements are arranged in order of A increasing:
(A) Atomic numbers
(B) Decreasing atomic number
(C) Increasing atomic masses
(D) Decreasing atomic masses.
Answer:
(C) Increasing atomic masses

Question 4.
Which element occupied gap left in Mendeleers periodic table?
(A) Germanium
(B) chlorine
(C) Oxygen
(D) Silicon.
Answer:
(A) Germanium

Question 5.
An element has the electronic configuration 2, 8, 2. It is present in group:
(A) 2
(B) is
(C) 8
(D) 10.
Answer:
(A) 2

Question 6.
Which element shows metallic character?
(A) 2, 8, 2
(B) 2, 8, 4
(C) 2, 8, 8
(D) 2, 7.
Answer:
(A) 2, 8, 2

Question 7.
Which shell is largest shell?
(A) K
(B)L
(C) M
(D) N.
Answer:
(D) N

Fill in the blanks :

Question 1.
Out of Na and Mg, ______ has bigger size.
Answer:
Na.

Question 2.
Number of elements known in Mendeleefs periodic table were ______
Answer:
63.

Question 3.
Oxygen and sulphur belong to same ______
Answer:
group.

Question 4.
The elements of group 17 are called ______
Answer:
halogens.

Question 5.
The valency of the members of noble gas family is ______
Answer:
zero.

Question 6.
The halogens belong to group ______
Answer:
17.

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 5 Periodic Classification of Elements Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 5 Periodic Classification of Elements

PSEB 10th Class Science Guide Periodic Classification of Elements Textbook Questions and Answers

Question 1.
Which of the following statements is not a correct statement about the trends when going from left to right across the periods of periodic table.
(а) The elements become less metallic in nature.
(b) The number of valence electrons increases.
(c) The atoms lose their electrons more easily.
(d) The oxides become more acidic.
Answer:
(c) The atoms lose their electrons more easily.

Question 2.
Element X forms a chloride with the formula XCl₂, which is a solid with a high melting point. X would most likely be in the same group of the periodic table as :
(a) Na
(b) Mg
(c) Al
(d) Si
Answer:
(b) Mg

Question 3.
Which element has :
(а) two shells, both of which are completely filled with electrons?
Answer:
Neon

(b) the electronic configuration 2, 8, 2?
Answer:
Magnesium

(c) a total of three shells, with four electrons in its valence shell?
Answer:
Silicon

(d) a total of two shells, with three electrons in its valence shell?
Answer:
Boron

(e) twice as many electrons in its second shell as in its first shell?
Answer:
Carbon.

Question 4.
(a) What property do all elements in the same column of the periodic table as Boron have in common?
Answer:
All elements of this column have 3 electrons in their valence shell like Boron.

(b) What property do all elements in the same column of the periodic table as Fluorine have in common?
Answer:
All elements of this column have 7 electrons in their valence shell like fluorine.

Question 5.
An atom has electronic configuration 2, 8, 7.
(а) What is the atomic number of this element?
Answer:
17

(b) To which of the following element would it be chemically similar? (atomic numbers are given in parenthesis).
N (7), F (9), P (15), Ar (18).
Answer:
F (9) (2, 7)

Question 6.
The position of three elements A, B and C in the periodic table are as shown below :

(а) State whether A is a metal or non-metal.
Answer:
A is non-metal.

(b) State whether C is more reactive or less reactive than A.
Answer:
C is less reactive than A.

(c) Will C be larger or smaller in size than B.
Answer:
C has smaller size than B.

(d) Which type of ion, cation or anion, will be formed by element A?
Answer:
Anion, A-.

Question 7.
Nitrogen (atomic number 7) and phosphorus (atomic number 15) belong to group 15 of the periodic table. Write the electronic configurations of these two elements. Which of these will be more electronegative? Why?
Answer:

	K	L	M
N7 has electronic configuration	2	5
P15 has electronic configuration	2	8	7

Nitrogen is more electronegative than Phosphorus due to smaller size.

Question 8.
How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?
Answer:
By knowing the electronic configuration of an element, we can know its period number from the number of shells present in its atom and from number of electrons in the valence shell of its atoms we can know its group number, e.g. let us consider the case of sodium atom.

Atomic number of sodium = 11
Its electronic configuration = 2, 8, 1 (K) (L) (M)
∴ Number of shells = 3
∴ Sodium belongs to 3rd period.

Also sodium atom has one electron in its valence shell.
∴ It is present in first group.
∴ Sodium lies in the first group and third period of Modern Periodic Table.

Question 9.
In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12,19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
Answer:
Element with atomic numbers 12 and 38 because they have two electrons in their valence shells like calcium (2, 8, 8, 2).

Question 10.
Compare and contrast the arrangement of elements in Mendeleev’s Periodic table and the Modern Periodic table.
Answer:
Similarities :

• In both the elements are arranged in groups and periods.
• In both similar elements are placed in same group.
• Both the classification make the study of elements simple and systematic.

Differences :

Mendeleev’s Periodic Table	Modern Periodic Table
1. The elements are arranged in order of increasing mass numbers.	1. The elements are arranged in order of increasing atomic numbers.
2. It has 8 vertical columns called groups.	2. It contains eighteen vertical columns called groups.
3. Groups like group VIII ‘have been divided into sub groups A and B.	3. Each group is an independent group.
4. Inert gases are not included in this table.	4. Inert gases are included in this periodic table.

Science Guide for Class 10 PSEB Periodic Classification of Elements InText Questions and Answers

Question 1.
Did Dobereiner’s triads also exist in the columns of Newlands’ octaves? Compare and find out.
Answer:
Yes, Dobereiner’s triads also existed in columns of Newlands’ octaves. These are:

H	Li	Be
F	Na	Mg
Cl	K	Ca

Question 2.
What were the limitations of Dobereiner’s classification?
Answer:

• Dobereiner could find only three triads from the elements known at that time.
• It is applicable only to a few elements.

Question 3.
What were the limitations of Newlands’ law of octaves?
Answer:

• It is applicable upto calcium only.
• Sometimes two elements were put in the same slot.
• After the discovery of noble gas, law of octave is not valid.

Question 4.
Use Mendeleev’s periodic table to predict the formulae for the oxides of following elements :
K, C, Al, Si, Ba.
Answer:
K₂O, CO₂, Al₂O₃, SiO₂, BaO.

Question 5.
Besides Gallium, which other elements have since been discovered to fill the gaps left by Mendeleev in his periodic table? (any two)
Answer:
Scandium and Germanium.

Question 6.
What were the criteria used by Mendeleev in creating his periodic table?
Answer:

• The formulae of hydrides and oxides formed by an element wrere treated as one of the basic properties of an element for its classification.
• It is based upon Mendeleev’s periodic law which predicts that the properties of the elements are the periodic function of their atomic masses.

Question 7.
Why do you think the noble gases are placed in a separate group?
Answer:
These gases were discovered very late because they are very inert and placing them in a separate group, does not disturb the existing order put forward by Mendeleev.

Question 8.
How could Modern Periodic Table remove various anomalies of Mendeleev Periodic Table?
Answer:

• Isotopes of an elements occupy same position in the periodic table due to same atomic number.
• There is a logical separation of elements into subgroups.
• It is based upon the fundamental property of an element i.e. atomic number.

Question 9.
Name two elements you would expect to show same kind of chemical reactivity as magnesium. What is the basis for your choice?
Answer:
Calcium and Strontium because they have same number of valence electrons.

Question 10.
Name :
(а) three elements that have only a single electron in their outermost shells.
Answer:
Lithium, Sodium and Potassium.

(b) two elements that have two electrons in their outermost shells.
Answer:
Magnesium, Calcium.

(c) three elements with filled outermost shells.
Answer:
Neon, Argon, Krypton.

Question 11.
(a) Lithium, Sodium, Potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
Answer:
One electron in their valence shells and are metals.

(b) Helium is an unreactive gas and neon is a gas of extremely low reactivity. What, if anything, do their atoms have in common?
Answer:
Eight electrons in their valence shells.

Question 12.
In the modern periodic table, of the first ten elements, which are metals?
Answer:
Lithium and Beryllium.

Question 13.
By considering their position in the periodic table, which one of the following elements would you expect to have the most metallic characteristics?
Ga Ge As Se Be.
Answer:
Gallium.

Punjab State Board PSEB 10th Class Science Important Questions Chapter 4 Carbon and its Compounds Important Questions and Answers.

PSEB 10th Class Science Important Questions Chapter 4 Carbon and its Compounds

Long Answer Type Questions

Question 1.
What is allotropy? Name the allotropes of carbon. Are they chemically same? Compare their physical properties.
Answer:
Allotropy: The phenomenon of existence of two or more different physical forms of the same chemical element, with same chemical properties is called allotropy.

Allotropes of carbon

• Diamond
• Graphite

Similarity in chemical composition:
If both the allotropes in equal amount are heated in air then both will release same amount of carbon dioxide and will not leave any residue. Therefore this proves that both are same in chemical composition.

Comparison of Physical Properties

Property	Diamond	Graphite
1. Appearance	Transparent	Black, shiny
2. Hardness	Very hard	Soft, slippery/ smooth in touch
3. Heat conductivity	Very less	Medium conductor
4. Electric conductivity	Bad conductor	Good conductor
5. Density (kg/m3)	3 – 510	2 – 250
6. Purity	Purest	Less pure than diamond
7. Melting point	3500°C	3000°C
8. Uses/Applications	Jewellery, drilling purpose Lubricants.	Drycells, Electric Arcs, Pencils, Lead,

Question 2.
What is covalent bond? Write its properties.
Answer:
The chemical bond formed by sharing of electrons between atoms of same or different non-metal elements is known as covalent bond.

Properties of Covalent bond/bonds.

• They hax e strong bonds within molecules but their inter molecular bond is weak.
• They have low boiling points.
• They have low melting points.
• Their compounds are bad conductors of electricity.

Question 3.
(a) Why does carbon form largest number of compounds?
Answer:
This is due to its tetracovalency and catenation.

(b) Why are some of these called saturated and other unsaturated compounds?
Answer:
The compounds containing C – C single bond are called saturated compounds and the compound containing

bonds are called unsaturated compounds.

(c) Which of these two is more reactive?
Answer:
Unsaturated compounds are more reactive than saturated compounds.

(d) Write the names of the compounds
(i) CH₃ – CH₂ – Br
Answer:

Answer:

Question 4.
Write about nomenclature of carbon compounds.
Answer:
The names of compounds in a homologous series are based on the name of basic carbon chain modified by a prefix’ ‘phrase before’ or ‘suffix’ ‘phrase after’ indicating the nature of the functional group. For example, the names of various alcohols are methanol, ethanol, propanol and butanol.

Naming of carbon compound can be done by the following method :

• Identify the number of carbon atoms in the compound. A compound having three carbon atoms will have the name propane.
• In case a functional group is present, it is indicated in the name of the compound with either a ‘prefix’ or a ‘suffix’. Like chloro propane, bromo propane, propanal, propanone etc.
• If the name of functional group is to be given on the basis of suffix, the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix. For example, a chain having three carbons with a Ketone group will be given name in the following manner.
  Propane-‘e’ = propan + ‘one’ = propanone.
• If the carbon chain is unsaturated then the final ‘ane’ in the name of carbon chain is substituted by ‘ene’ or ‘yne’. For example, a three-carbon chain with a double bond would be called propene and if it has triple bond, it would be called propyne.

Question 5.
Write down the chemical properties of carbon compounds.
Answer:
The main chemical properties of carbon compounds are :
1. Burning: Carbons in all its allotropic forms burns in the presence of oxygen and produces heat, light and C02, For example :
C + O₂ → CO₂ + heat and light
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat and light
CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + Heat and light.
Saturated hydrocarbons burn with a clear flame whereas unsaturated hydrocarbons burn with sooty yellow flame.

2. Oxidation: Carbon compounds can easily be oxidised by burning. Alkaline potassium permanganate or acidified potassium permanganate converts alcohols into acids.

3. Addition reaction: Unsaturated hydrocarbons make saturated hydrocarbons by adding hydrogen to itself in the presence of catalysts like nickel and palladium. The reaction is commonly used in hydrogenation of vegetable oils using nickel catalyst.

Vegetable oils generally have long unsaturated carbon chain while animal fats have saturated carbon chains.

4. Substitution reaction: Saturated hydrocarbons are fairly unreactive and are inert in the presence of most reagents. However, in the presence of sunlight, chlorine gets combined with hydrocarbons in a quick reaction. Chlorine replaces very quickly the hydrogen atoms in the chemical reaction one by one due to which number of products are usually formed with the higher homologous of alkanes.

Question 6.
(a) What is an alcohol? Give two examples.
Answer:
Alcohol is a simple compound of carbon, hydrogen and oxygen. If one hydrogen atom is replaced by hydroxyl (-OH) group in alkene, alcohol is produced. General formula of alcohol is C_nH_2n+2

Examples :

• In Methane (CH₄) when hydrogen atom is replaced by hydroxyl (- OH) group, methanol (CH₃OH) is formed.
• Ethanol (C₂H₅OH) is produced with the help of ethane

(b) How is synthetic ethanol produced? Also write.
Answer:
Synthetic ethanol is prepared by reacting ethane with water in the presence of phosphoric acid (H3P04).

Properties of Ethanol :

• It is a colourless liquid with specific colour.
• Its boiling point is 351 K and melting point is 156 K.
• It is soluble in water in any proportion.
• It doesn’t show any reaction with litmus because it is neutral.
• It burns with blue flame in air to produce carbon dioxide and water.
  C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O
• It reacts with oxygen or potassium dichromate (K₂Cr₂O₇) to produce ethanoic acid.
  C₂H₅OH + O₂ → CH₃COOH + H₂O
• It reacts with sodium metal.
  2C₂H₅OH + 2Na → 2C₂H₅ONa + H₂
• It reacts with acetic acid in the presence of concentrated H₂SO₄. When this mixture is heated and poured in ice cold solution of sodium carbonate, a sweet smell is produced.

Question 7.
Give important properties of monocarboxylic acids. Also give its uses.
Or
Give important properties of ethanoic acid (Acetic acid). Also give its uses.
Answer:
Important properties of monocarboxylic acid :
1. Ethanoic acid or acetic acid is colourless liquid and is soluble in water, 5-8% solution of acetic acid in water is called vinegar.

2. Pure ethanoic acid melts at 290 K and freezes during winter in cold climates and looks like ice. Hence it is called glacial acetic acid.

3. Esterification: When an acid is heated with an alcohol in the presence of cone. H2S04, an ester is produced. This is a slow reversible reaction and is called esterification.

Esters are sweet-smelling substances.

4. Action with a base

5. Action with carbonates and bicarbonates
Ethanoic acid decomposes carbonates and bicarbonates producing salt, carbon dioxide and water.
2CH₃COOH + Na₂CO₃ → 2CH₃COONa + H₂O + CO₂ ↑
CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂ ↑

Uses of ethanoic acid :

• It is used in the manufacture of dyes, perfumes and rayon.
• It is used in the manufacture of plastics, rubber and silk industries.
• It is used as a solvent.
• It is used as a vinegar in cooking, as food dressing and for preparing pickles.
• It is used for the manufacture of chemicals like acetone, acetic anhydride, etc.
• It is used for making white lead [2PbCO₃. Pb(OH)₂]

Question 8.
Explain the following terms :
(i) Esterification
Answer:
Alcohols are treated with carboxylic acids in the presence of concentrated sulphuric acid to form ester and this process in known as esterification.

Method: Mix ethyl alcohol with acetic acid in a test tube. Few drops of concentrated sulphuric acid is added and test tube is heated mildly in hot tub of water. Instantaneously sweet smell of ester is diffused in whole room.

It is an example of esterification. Ester is used in ice-cream, cold drinks, medicines, make up etc.

(ii) Saponification
Answer:
Saponification: Breaking down of fats is called saponification.

It is performed by heating vegetable or animal oils with 40% solution of caustic soda. Fats and base react to produce soap and glycerol.

Concentrated common salt solution is added to crystallize soap from water. Soap floats on the surface of water, after cooling. Soap is extracted from water and desired colour and smell are added and is given desired shape.

(iii) Decarboxylation
Answer:
Decarboxylation: Methane is produced when sodium or potassium salt of ethanoic acid are heated with sodium hydroxide and calcium oxide in 3 : 1 ratio.

It is a useful method to prepare methane. It is known as decarboxylation because one molecule of CO₂ is removed.

(iv) Polymerization.
Answer:
Polymerization: When a large number of small molecules join together at a specific temperature and pressure to form a big molecule, this process is termed as polymerization. These small molecules are known as ‘monomer’ whereas big combined molecule is known as ‘polymer.’
For example. Molecules of ethene join together at 2000 atm pressure and 200°C to form polythene.

Question 9.
Describe a method for the preparation of soap.
Answer:
Soaps are sodium or potassium salts of higher fatty acids. When the naturally occurring esters called fats or oils are heated with NaOH solution, they undergo hydrolysis to form sodium salt of higher fatty acid (called soap) and glycerol.

Manufacture of Soap. Soap can be made easily in the laboratory. Heat fat or oil with sodium hydroxide solution. After a few minutes, and constant stirring, the oil and water layers get mixed.

Add 5-10 g of common salt to it, stir the mixture and allow’ it to cool. On cooling, pale yellow a solid forms as a cake called soap.

The same principle is used for making soap in soap industry. Some other substances like perfumes, disinfectants and medicines are added to soap to give it desired characteristics.

Example :

Question 10.
What do you understand by isomers? Explain it with an example.
Or
Write down the isomers of butane.
Answer:
Isomers. The compounds with same molecular formula but different structural formula are called isomers and the phenomenon is called isomerism. There is no change in the structure of methane, ethane, propane if the atoms of carbon and hydrogen are rearranged but in case of alkane molecule if number of carbon is more than three then more than one arrangement is possible.

In this one long carbon chain is formed and the others are branched. In case of butane the chain is linked with atleast three carbon atoms with other carbon atoms. This type of alkanes are termed as iso-alkane. In a chain having no branch, carbon atom cannot be linked with two carbon atoms. Alkanes of this type are called normal alkane (n-alkane).

Two Isomers of Butane:

Isomers of Pentane

Short Answer Type Questions

Question 1.
Explain why carbon forms mostly covalent compounds?
Answer:
Carbon has four electrons in its outermost shell. In order to get stable electronic configuration, it has to lose or gain four electrons, but it is difficult to lose or gain four electrons from energy considerations. Hence, Carbon complete its octet by sharing its valence electrons with other atoms forming covatent bonds resulting in the formation of covalent compounds.

Question 2.
In order to form large amount of carbonic compounds which major elements are used other than hydrogen and oxygen?
Answer:
The number of carbonic compounds is very large which was not possible only with the help of hydrogen and oxygen. Along with these two elements some other elements like nitrogen, sulphur, oxygen, halogens (Cl, Br, I, F) etc. also combine and because of it the caybonic compounds have crossed the number of many million. These combine together on the basis of functional groups and make new compounds.

Question 3.
‘Carbon is a unique element’, why?
Answer:
Carbon is the only known element out of all other known elements, that has got capability to make long chains. Each long chain of carbon atoms provides such a simple base with which other atoms can join by various methods resulting in the composition of various compounds.

Carbon atoms can make long chains or rings in three ways because of having catenation property.

Question 4.
Explain the structure of diamond and write why is it so hard?
Answer:
In diamond each carbon atom remains at the centre of regular tetrahedral and it remains bound with covalent bond to four carbon atoms which are situated at four corners of tetrahedral. Thus, all electrons of carbon are bound atoms and none is found in free state. So it forms a strong three-dimensional tetrahedral structure and because of it diamond is the hardest substance with very high density.

Question 5.
What are the uses of diamond?
Answer:
Uses of Diamond

• Diamond being the hardest substance is used for cutting other substances.
• Diamond because of its shine and lustre is used for making ornaments.
• It is used for drilling hard rocks.
• Sharp-edged diamonds are used by eye surgeon in catract surgery.
• Being extra ordinarly sensitive for heat radiations and having property to remove immediately harmful radiations. These are used in making absolute thermometers.

Question 6.
Why do diamonds glitter?
Answer:
Diamond is a transparent substance whose refractive index is very high. The rays of light passing through it get diverted much. According to its cut base edges light rays undergo total internal reflection. When these edges are polished, diamond glitters very beautifully.

Question 7.
How are diamonds made naturally and artifically?
Answer:
Naturally, diamonds are made by carbon present at the depth of about 150 km, where pressure is 70,000 atm and the temperature is about 1500°C. These diamonds come up near the surface with special kimberlite rocks. Artifically, diamonds are made by heating graphite under high pressure in the presence of special catalysts.

Question 8.
Write the structure of graphite. Why is it so soft?
Answer:
Each carbon atom is bonded with three neighbouring carbon atoms with covalent bonds in graphite. They are always in the same plane giving hexagonal array. As compared to diamond, the distance between carbon atoms is more. The distance between upper and lower layers does not permit carbon atoms to make covalent bonds and because of this fourth electrons remains free. These layers can easily slide one upon the other and graphite attains the property of a lubricant. It is very soft and slippery.

Question 9.
Why are diamonds used in jewellery? Give reasons.
Answer:
Refractive index of diamond is 2.45 which is the highest of all known substances, because of this, it shines brightly. Its critical angle is 24°, which is very less. This is why, the light rays passing through it deviates much. A small deviation in it causes beautiful spectrum of colours. When the bases of diamond are polished, it produces an astonishing brightness. That is why diamonds are used in making jewellery.

Question 10.
Why is graphite a good conductor of electricity?
Answer:
Each carbon atom of graphite is surrounded by three carbon atoms joined with covalent bond which makes hexagonal layers over each other. In these layers distance between the carbon atoms is more, that is why the possibility of fourth covalent bond between the carbon atoms of opposite layers is reduced. The fourth covalent electron is set free. The graphite has easy flow of electrons and it acts as a good conductor of electricity.

Question 11.
What are the uses of graphite?
Answer:
Uses of Graphite

• It is good conductor of electricity so- it is used in making dry cells and electric arcs as electrods.
• It is used in making pencils, black colour and black paint.
• It has lubricant property so it is used in machines to keep them lubricating at high temperature.
• It is used in making crucibles to boil some metals because of its high melting point.

Question 12.
Why are allotropes of carbon in form a molecule known as fullerenes?
Answer:
The allotropes of carbon in which 60 carbon atoms join to form a molecule are termed as fullerene. US architect Buckminster Fuller designed three dimensional domes which were supported by pentagonal and hexagonal structures.

Since fullerene molecules looked like these domes, that is why they are known as fullerene.

Question 13.
Draw the electron dot structures of methane, ethane, ethene, butane.
Or
(i) Write molecular formula of butane.
(ii) Draw the structure of Propanal.
Answer:
Methane
Formula -CH₄

Ethane
Formula -C₂H₆

Ethene
Formula -C₂H₄

Or
(i) Butane
Formula – C₄H₁₀

(ii) Propanal

Question 14.
Write two tests of alcohol.
Answer:

1. Ester test: When alcohol is heated with acetic acid, in the presence of sulphuric acid, sweet smelling ester is produced.
2. Sodium test: Alcohol reacts with sodium metal and always produces hydrogen gas.

Question 15.
(a) What do you understand by homologous series? Explain with an example.
Answer:
Homologous series. A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called a homologous series. Each successive member differ by (- CH₂) group. All the members of a homologous series can be obtained by similar process.

General Formula : C_nH_2n+2
For example : Homologous series of alkane is as follows

(b) Write the first three homologous compounds of methane.
Answer:
Homologous Compounds of Methane

Question 16.
Define homologous series. What are its main properties?
Answer:
Homologous series. A series of compounds in which the same functional group substitutes for hydrogen in a carbon chain is called homologous series. In this series the adjacent members differ by (-CH₂) group. Each member of a homologous series is called homolog.

Properties of Homologous Series :

• All the members of a homologous series can be represented by a common formula.
• Two successive members differ by one carbon atom and 2 hydrogen atoms.
• All the members of a homologous series possess similar chemical properties.
• There is a small difference between all the members of a homologous series.
• There is always a difference of 14 a.m.u. in atomic mass of two adjacent homologous.

Question 17.
What are alkanes? Write the properties of its main members. What do we conclude from its properties?
Answer:
Alkanes. The hydrocarbons with structural/general formula C_nH_2n+2 are called alkanes. The members of this group form an homologous series. Hydrocarbons like methane, ethane, propane and butane form many carbonic compounds which are collectively known as alkane. In these compounds, the number of carbon and hydrogen atoms differ by (- CH₂) for the next member of family.

Properties of Alkanes

Conclusions:

• Physical properties of alkane are based on their mass.
• First four members of alkane are in gasous state and alkanes having more than six carbon atoms are in liquid state.
• Alkanes having high molecular mass are found in solid state.
• Melting and boiling point of alkanes increase with increase in molecular mass.

Question 18.
What happens when hydrogen gas is passed through vegetable oils in the presence of nickel?
Answer:
Vegetables oils have double bond and polymerisation is possible. When nickel is used as catalyst, vegetable oil converts to vegetable ghee when hydrogen is passed through it because of hydrogenation. Vegetable ghee is solid like butter at room temperature.

Question 19.
Write the chemical properties of ethanoic acid.
Answer:
Ethanoic acid reacts with some metals, metal carbonates, hydroxides and bicarbonates.
1. Action with sodium:

2. Action with sodium hydroxide and potassium hydroxide:

3. Action with carbonate and hydrogen carbonate :
It reacts with carbonates and hydrogen carbonate to form water, salt and carbon dioxide.

Question 20.
Which type of oils should be used for cooking? Why?
Answer:
Animal fats have saturated fatty acids, which are harmful for health, whereas oils have long unsaturated carbon chains which are not harmful. Hence unsaturated fatty acids oils are used for cooking.

Question 21.
Write the ill-effects of using alcohol.
Answer:

• It is an addictive substance.
• It affects the sensitivity of nervous system.
• When a drunken person drives the vehicle he/she is not able to take the right decisions which leads to accident.

Question 22.
Why is consumption of methanol (CH₃OH) very fatal?
Answer:
Even a very small amount of methanol can prove fatal. In liver, it oxides to form methanale, which vigorously react with cells of liver, by which protoplasm gets emanating and swells in the same manner as boiled egg. Consumption of methanol also lead to blindness.

Question 23.
Write the IUPAC names of ethyl alcohol and acetic acid. Write the name of products formed when ethyl alcohol and acetic acid react in the presence of concentrated sulphuric acid. Write its chemical reaction.
Answer:

Compounds	IUPAC Names
1. Ethyl alcohol	ethanol
2. Acetic acid	ethanoic acid

Chemical reaction :

Question 24.
How will you prepare :
(a) ethyl alcohol from ethene
(b) acetic acid from ethyl alcohol?
Give reactions.
Answer:
(a) Ethene is heated with water in the presence of phosphoric acid to prepare ethyl alcohol

(b) Acetic acid is prepared by oxidation of ethyl alcohol

Question 25.
Write in brief the various industrial alcohols.
Answer:

• Absolute alcohol: It is 100% pure ethanol. It is produced by fractional distillation of ethanol which is prepared by fermentation of carbohydrates.
• Denatured alcohol: It is 95% ethanol and is used in industries. It is made poisonous by adding methanol, copper sulphate and pyridine, so as to make it unfit for drinking.
• Power alcohol: It is mixture of Benzene and Ether in 20% Ethanol and 50% gasolene. It is used to save petroleum.
• Alcoholic beverages: Alcohol is used as addictive drink. It is sold under various names like, rum, whisky, brandy, Jinn, etc.

Question 26.
Why is cleansing effect of soap not effective in hard water?
Answer:
Soaps are not effective in hard water for washing purposes because hard water has salts of calaium and magnesium. When soaps are dissolved in hard water, calcium and magnesium ions l’eact with water to form calcium and magnesium salts of fatty acids.

That is why a large amount of soap gets wasted. Calcium and magnesium salts being insoluble in water make precipitates and they get attached with the clothes and cause hinderance to the cleaning action and the clothes are not cleaned properly.

Question 27.
Distinguish between soaps and detergents.
Answer:

Soaps	Synthetic detergents
1. Soaps are sodium or potassium salts of higher fatty acids e.g. Sodium Stearate.	1. Synthetic detergents are Sodium alkyl Sulphates or Sodium alkyl benzene sulphates.
2. Soaps are prepared from vegetable oils or animal fats.	2. Synthetic detergents are prepared from the hydrocarbons obtained from petroleum.
3. Soaps have relatively weak cleansing action.	3. They have strong cleansing action.
4. Soaps form curdy white precipitates with calcium and magnesium salts present in hard water and hence, are not used in hard water.	4. Calcium and magnesium salts of detergents are soluble in water. Therefore no curdy white precipitates are obtained in hard water and hence synthetic detergents can be used even in hard water.
5. Soaps cannot be used in acidic medium as they are decomposed into carboxylic acids in acidic medium.	5. They can be used in acidic medium as they are the salts of strong acid and are not decomposed in acidic medium.
6. Soaps do not cause water pollution.	6. Synthetic detergents cause water pollution.
7. Soaps are biodegradable.	7. Some of the synthetic detergents are non biodegradable.

Question 28.
Write the formation of ethanol by fermentation process.
Answer:
Fermentation occurs in the presence of Bio-chemical catalysts at normal temperature by which sugar molecules convert into alcohol and carbon dioxide. These catalysts are known as enzymes, which means ‘yeast’ or ‘in the fermentation’.

Alcohol is formed by fermentation of sugar or starch. In a beaker, grape juice or glucose mixture is heated at 20° – 30°C in the presence of yeast. Sugar or starch molecules break into smaller molecules which produce carbon dioxide due to process of fermentation. This carbon dioxide is expelled out but air is not given inlet. A dilute mixture of ethanol is formed in water during fermentation. Ethanol is purified by distillation.

Chemical reaction :

Question 29.
Write the name of the reaction in which ethanoic acid and ethanol react together to form one product. Write the common name of the product.
Answer:
When ethanoic acid reacts with ethanol in the presence of concentrated sulphuric acid, ester is produced and this process is known as esterification.
CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O

Question 30.
Observe the figure given below :

(i) Write the reaction taking place
Answer:

(ii) What is this reaction called?
Answer:
Esterification

Question 31.
What is indicated in the figure given below and give use of it.
Answer:
The figure indicates formation of micelle. Micelles are used to remove oily dirt from clothes.
1 – Hydrophilic end
2 – Oil droplet.

Question 32.
Show the bonds of Hydrogen, Oxygen and Nitrogen atoms respectively.
Answer:
1. Hydrogen: Two atoms of hydrogen by sharing of their electrons make hydrogen molecule (H2).

2. Oxygen: A double bond is made between two atoms of oxygen. Each atom of oxygen shares two electrons with other atom to form .an octet.

3. Nitrogen: Each atom of nitrogen shares three electrons to form an octet.

Question 33.
(i) Write molecular formula of Propane.
Answer:
C3H8

(ii) Write IUPAC name of

Answer:
Bromoethane.

Question 34.
What is detergent? Write the formation of synthetic detergents. Write its advantage.
Answer:
Materials used for cleaning purposes are known as detergents. Since long, soaps have been used as detergents but now-a-days synthetic detergents are more popular. The detergent molecule has two ends, one which is made of sulphate (-SO₄) or sulphonate (SO₃Na) group and it is hydrophilic by nature whereas other which is made of hydrocarbon is hydrophobic.

Synthetic detergent produces ample amount of lather even in hard water. These do not form insoluble salts of calcium or magnesium.

Question 35.
Which substances are used to produce synthetic detergents?
Answer:
Following substances are needed for production of synthetic detergents :

• Long chained hydrocarbons obtained from petroleum and coal.
• Concentrated sulphuric acid.
• Sodium hydroxide.

Procedure: Hydrocarbons are treated with cone, sulphuric acid to get hydrocarbonic sulphuric acid. It is further reacted with NaOH which forms synthetic detergents. About 15 to 30% of the total weight of washing powder is detergent. Rest of the others are various chemicals which provide other qualities.

Question 36.
What are the components of washing powder?
Answer:

• Synthetic detergents (15 to 30%).
• Sodium sulphate and sodium nitrate.
• Sodium tri-poly phosphate or sodium carbonate.
• Sodium perborate.

Very Short Answer Type Questions

Question 1.
Which element is present necessarily in the following items?
Food, clothes, medicines and hooks.
Answer:
Carbon.

Question 2.
On which element do all living processes depend?
Answer:
Carbon.

Question 3.
What percentage of carbon is present in minerals found under the crust of earth?
Answer:
0.02 %.

Question 4.
What percentage of CO₂ is present in atmosphere?
Answer:
0.003%.

Question 5.
How many electrons are present in the outer shell of carbon?
Answer:
4.

Question 6.
Why does carbon need four electrons to gain or lose?
Answer:
To attain noble gas configuration.

Question 7.
How does carbon gain four electrons?
Answer:
By making C₄^– anion.

Question 8.
How does carbon lose four electrons?
Answer:
By making C₄⁺ cation.

Question 9.
Which type of bond is shared by a pair of two hydrogen atoms?
Answer:
Single bond.

Question 10.
How is single bond between two atoms expressed?
Answer:
By single straight line.

Question 11.
What is the atomic number of nitrogen?
Answer:
7.

Question 12.
How many electrons are given by each atom of Nitrogen to complete the octet?
Answer:
3.

Question 13.
Which gas is used as a fuel the most?
Answer:
Methane gas.

Question 14.
Methane is the main constituent gas of which two fuel gases?
Answer:
Biogas, C.N.G.

Question 15.
Write the full form of C.N.G.
Answer:
Compressed Natural Gas.

Question 16.
How is the structure of diamond?
Answer:
Strong three-dimensional structure.

Question 17.
How is the structure of graphite?
Answer:
Hexagonal.

Question 18.
Which of these two is a good conductor of electricity diamond or graphite?
Answer:
Graphite.

Question 19.
Which is the hardest substance?
Answer:
Diamond.

Question 20.
How does it feel by touching graphite?
Answer:
Soft and slippery.

Question 21.
Which element has the ability to form large number of compounds?
Answer:
Carbon.

Question 22.
Give names of two elements which are placed in the group of carbon and have same valency.
Answer:
Valency of carbon is 4. This group has silicon and germanium.

Question 23.
What is the simplest form of hydrocarbon?
Answer:
Methane (CH₄).

Question 24.
In which types of bonds can carbon atoms join?
Answer:
Single, double, triple bond and ring-shaped.

Question 25.
Write the names of five elements which can make bond with carbon to form new compounds.
Answer:
Oxygen, Hydrogen, Nitrogen, Sulphur, Chlorine.

Question 26.
Write the formula of Ethane.
Answer:
C₂H₆.

Question 27.
Write the structural formula of Ethane.
Answer:

Question 28.
Give the next higher homo-logues of:
(i) C₃H₆
Answer:
C₄H₈

(ii) C₆H₈.
Answer:
C₇H₁₀.

Question 29.
Give the structure of ethanol.
Answer:

Question 30.
Name the functional group in propanone.
Answer:

Question 31.
Give the structure of simplest ketone.
Answer:
Simplest keton is acetone. It has the structure :

Question 32.
Give the name and structure of four carbon atoms in aldehyde.
Answer:

Question 33.
Name the products obtained when ethanol undergoes complete combustion.
Answer:
Carbon dioxide (CO₂) and Water (H₂O).

Question 34.
Give the structural formula of ethanol.
Answer:

Question 35.
Give the name and structure of functional group present in acetic acid (CH3COOH).
Answer:
Carboxyl group

Question 36.
Which of the following compounds belong to same homo-Iogous series?
C₂H₆O₂, C₂H₆O₂, C₂H₆, CH₄O
Answer:
C₂H₆ O, (C₂H₅OH) And CH₄O or (CH₂OH).

Question 37.
Give the structural formula of an ester.
Answer:

Question 38.
Give the names and structural formulas of acid and alcohol from which ethyl acetate is obtained.
Answer:
Acetic acid

and ethyl alcohol, CH₃CH₂OH

Question 39.
Give the electron-dot stucture of methane.
Answer:

Question 40.
Define covalent bond.
Answer:
It is formed by mutual sharing of electron pair between two atoms.

Question 41.
Explain what covalent compounds do not conduct electric current?
Answer:
This is because there are neither free ions nor free electrons.

Question 42.
Name the bond formed between metal atom and non-metal atoms.
Answer:
Ionic or electro valent bond.

Question 43.
What are allotropes?
Answer:
When an element exists in two or more form having different physical pruperties but, some chemical properties, there forms are called allotropes.

Question 44.
Define catenation.
Answer:
It is the property due to which a large number of atoms of the same element get linked together through covalent bonds forming long straight chains, branched chains and rings of different sizes.

Question 45.
Give two oxidising agents.
Answer:

1. Acidified potassium permanganate.
2. Acidified potassium dichromate.

Question 46.
Give the electron dot structure of ethane.
Answer:
Dot structure of ethane :

Question 47.
Give the structural formula of propane.
Answer:

Question 48.
Give the electron dot structure of ethene.
Answer:
Dot structure of ethene.

Question 49.
Define functional group.
Answer:
It is an atom or group of atoms which when present in a molecule gives special properties to it. e.g. C₂H₅OH has the functional group, -OH (hydroxyl group).

Question 50.
If two organic compounds have some functional group, predict they have similar physical or chemical properties.
Answer:
Similar chemical properties.

Question 51.
Give the general formulae of alkanes, alkenes and alkynes.
Answer:
Alkanes: C_n H_2n+2
Alkaenes: C_nH_2n
Alkynes: C_nH_2n-2, where n = No. if carbon atoms).

Question 52.
Give the structural formula of isomers of C₄H₁₀ (butane).
Answer:
Butane has two structural isomers :

Question 53.
Give the first four members of homologous series of alcohols.
Answer:
CH₃OH, C₂H₅OH. C₃H₇OH, C₄H₅OH.

Question 54.
Define a Catalyst.
Answer:
It is a substance which can increase the rate of a reaction but remains unchanged in mass and composition at the end of reaction.

Question 55.
What happens when a piece of sodium metal is added to ethanol? Give chemical equation also.
Answer:

Question 56.
What happens when ethanol is heated with conc. H₂SO₄ at 443K?
Answer:
Ethanol undergoes acidic dehydration to give ethene

Question 57.
What is denatured spirit or alcohol?
Answer:
It is prepared by adding poisonous substance like methanol, acetone, pyridine or copper sulphate to ethanol. It is unfit for drinking purposes.

Question 58.
Give three uses of ethanoic acid.
Answer:

1. In the manufacture of vineger
2. In the manufacture white lead
3. As a reagent in laboratory.

Question 59.
What is the atomic number of hydrogen?
Answer:
One.

Question 60.
Give the electronic configuration of carbon atom.
Answer:
(2, 4).

Question 61.
Give name of four carbon compounds.
Answer:
Methane, Chloroform, Ethanol and ethanoic acid.

Question 62.
Give two allotropic forms of carbon.
Answer:
Diamond and graphite.

Question 63.
Give the name of simplest ketone.
Answer:
Propanone (CH₃ COCH₃).

Question 64.
Give the name of first member of homologous series of alkynes.
Answer:
Ethyne (C₂H₂).

Question 65.
Give the name and formula of acid present in vinegar.
Answer:
Ethanoic acid (CH₃ COOH).

Multiple Choice Questions:

Question 1.
Ethanoic acid has the formula:
(A) C₂H₅OH
(B) CH₃COCH₃
(C) CH₃COOH
(D) C₂H₅COOH.
Answer:
(C) CH₃COOH

Question 2.
Carboxylic acids contain functional group:
(A) -CHO
(B) -CH₂OH
(C) -COOH
(D) -OH.
Answer:
(C) -COOH

Question 3.
The general formula of the alkyne is:
(A) C_nH_2n-2
(B) C_nH_2n+2
(C) C_nH_2n
(D) C_nH_2n+2.
Answer:
(A) C_nH_2n-2

Question 4.
Propanone has the functional group :
(A) -OH
(B) -CHO
(C) C=O
(D) -COOH.
Answer:
(C) C=O

Question 5.
Vinegar contains acetic acid:
(A) 5-8%
(B) 15-20%
(C) 21-29%
(D) 30-40%.
Answer:
(A) 5-8%

Question 6.
The reaction of acetic acid with ethyl alcohol is called :
(A) Polymerisation
(B) Saponification
(C) Hydrogenation
(D) Esterification.
Answer:
(D) Esterification.

Fill in the Blanks :

Question 1.
The functional group present in ethyl alcohol is ___________
Answer:
The functional group present in ethyl alcohol is alcoholic group (-OH)

Question 2.
CH₃—CH₂—OH represents ___________
Answer:
Ethyl alcohol.

Question 3.
Two atoms of the same element combine to form a molecule. The bond between them is known as ___________ bond.
Answer:
Covalent.

Question 4.
In the formation of oxygen molecule, the oxygen atoms share ___________ electrons each.
Answer:
Two.

Question 5.
The number of single covalent bonds in the molecule of ammonia is ___________
Answer:
Three.

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 4 Carbon and its Compounds Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 4 Carbon and its Compounds

PSEB 10th Class Science Guide Carbon and its Compounds Textbook Questions and Answers

Question 1.
Ethane, with the molecular formula C₂H₆ has :
(a) 6 covalent bonds
(b) 7 covalent bonds
(c) 8 covalent bonds
(d) 9 covalent bonds.
Answer:
(b) 7 covalent bonds

Question 2.
Butanone is a four-carbon compound with the functional group :
(a) carboxylic acid
(b) aldehyde
(c) ketone
(d) alcohol.
Answer:
(c) ketone

Question 3.
While cooking, if the bottom of the vessel is getting blackened on the outside, it means that :
(а) the food is not cooked completely
(b) the fuel is not burning completely
(c) the fuel is wet
(d) the fuel is burning completely.
Answer:
(b) the fuel is not burning completely

Question 4.
Explain the nature of the covalent bond using the bond formation in CH₃Cl.
Answer:
The formation of CH₃Cl can be represented as :

Carbon forms single covalent bonds with three H- atoms and one Cl – atom by sharing one electron pair with each C-H bonds are non-polar. But C – Cl bond is polar because C and H leave almost same electronegativity whereas Cl has more electronegativity than carbon.

Question 5.
Draw the electron dot structures for :
(a) ethanoic acid
Answer:

(b) H₂S
Answer:

(c) propanone
Answer:

(d) F₂.
Answer:

Question 6.
What is an homologous series? Explain with an example.
Answer:
A series of compounds having similar structural formulae, same functional group and hence similar chemical properties is called a homologous series. In the homologous series any two adjacent members differ by CH2 unit in their molecular formulae.

For example homologous series of aldehydes (or alkanals) can be represented as :

H – CHO	Methanal
CH3 – CHO	Ethanal
CH3 – CH2 – CHO	Propanal
CH3 – CH2 – CH2 – CHO	Butanal
CH3 – CH2 – CH2 – CH2 – CHO	Pentanal and so on.

Question 7.
How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
Answer:
Differences between ethanol and ethanoic acid

Ethanol	Ethanoic acid
1. It is a colourless liquid having a pleasant smell.	1. It is colourless liquid having vineger like smell.
2. It has no action with a litmus solution.	2. It turns blue litmus solution red.
3. It has no action with sodium hydrogen carbonate solution.	3. It decomposes sodium hydrogen carbonate solution giving brisk effervescence of carbon dioxide gas.

Question 8.
Why does micelle formation take place when soap is added to water? Will a micelle be formed in other solvents such as ethanol also?
Answer:
Soap molecule has two ends, one is hydrophilic, and it dissolves in water, while the other end is hydrophobic, and it dissolves in hydrocarbons. When soap is at the surface of water , the hydrophobic ‘tail’ of soap will not be soluble in water and the soap will align along the surface of water with the ionic end in water and the hydrocarbon ‘tail’ pointing out of water.

Inside water, these molecules have a unique orientation which keeps the hydrocarbon portion out of the water. This is achieved due to the formation clusters of molecules in which the hydrophobic tails are in the interior of the cluster and the ionic ends are on the surface of the cluster. This formation is called a micelle.

Such micelles can be formed in other polar solvents like ethanol.

Question 9.
Why are carbon and its compounds used as fuels for most applications?
Answer:
Carbon and its compounds are used as fuels for most applications because they bum producing a large amount of heat and light.

Question 10.
Explain the formation of scum when hard water is treated with soap.
Answer:
When soap is added to hard water, the soluble calcium and magnesium salts present in it react with soap to give insoluble calcium salt of soap which produces scum.

Question 11.
What change will you observe if you test soap with litmus paper (red and blue)?
Answer:
Soap solution will turn red litmus paper blue because soap is alkaline in nature.

Question 12.
What is hydrogenation? What is its industrial application?
Answer:
The addition of hydrogen to unsaturated hydrocarbons in the presence of catalysts like palladium, platinum, nickel etc. to give saturated hydrocarbons is called hydrogenation.

This reaction is used for hydrogenation of liquid vegetable oils using a nickel catalyst to get artificial or vanaspati ghee.

Question 13.
Which of the following hydrocarbons undergo addition reaction : C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄.
Answer:
Out of C₂H₆, C₃H₈, C₃H₆, C₂H₂ and CH₄; C₃H₆ and C₂H₂ undergo addition reactions because they contain multiple bonds.

Question 14.
Give a test that can be used to differentiate chemically between butter and cooking oil.
Answer:
Distinction between Butter and Cooking oil:

Butter	Cooking Oil
1. It is solid at room temperature.	1. It is liquid at room temperature.
2. Mix equal volumes of HgCl2 solution in 50% alcohol and 5% iodine solution in alcohol. To this add lg of butter. Violet colour does not fade away.	2. Mix equal volumes of HgCl2 solution in 50% alcohol and 5% solution of iodine in alcohol. To this add 1 ml of cooking oil. Violet colour fades away.
3. Take 2 g of butter in a test tube. To this add 1ml of cone. HCl and a few drops of 2% furfural solution in alcohol. Shake and allow to stand for 5 – 10 minutes. No rose red coloration appears.	3. Take 2 g of cooking oil in a test tube. To this add 1 ml of cone. HCl and a few drops of 2% .furfural solution in alcohol. Shake it and allow to stand for 5 – 10 minutes. Rose red coloration is obtained.

Question 15.
Explain the mechanism of the cleansing action of soaps.
Answer:
Mechanism of cleansing action of Soap:
Soaps are sodium or potassium salts of higher fatty acids e.g. sodium palmitate, C₁₅H₃₁COO^–Na⁺, sodium stearate, C₁₇H₃₅COO^–Na⁺ etc. A molecule of soap consists of two parts :

1. a long chain hydrocarbon part (C₁₅H₃₁^–, C₁₇H₃₅ …. etc.) which is soluble in oil and
2. ionic part on polar group, – COO^–Na⁺ which is soluble in water. Thus a molecule of soap can be represented as :

The long hydrocarbon chain is insoluble in water but soluble in oil and greases whereas the ionic or polar part is soluble in water. Soap has a capacity to clean a dirty piece of cloth whereas ordinary water cannot. The dirty clothes contain greasy and oily substance (dirt). Soap molecules dissociate in water to give carboxylate ion (RCOO^–) and cation (Na⁺). When soap added to dirty clothes dipped in water, the hydrocarbon part of carboxylate group dissolving in greasy or oily dirt particles where the polar (COO^–) group remain attached to water. In this way each oil droplet acquires negative charge.

The cleansing action of Soap

These negative charged oil droplets called micelles cannot coalesce and hence form a stable emulsion water. These small droplets along with dirt can be easily washed away with water. Thus the soap helps in removing greasy dirt by producing a stable oil in wrater type emulsion. Also the soap reduces surface tension of water. Hence cloth is wetted more effectively and is cleaned.

Science Guide for Class 10 PSEB Carbon and its Compounds InText Questions and Answers

Question 1.
What would be the electron-dot structure of carbon dioxide which has the formula CO₂?
Answer:
In carbon dioxide, carbon atoms are bonded with two oxygen atoms. The atomic number of carbon is 6, and it has four electrons in the outer shell.

To make an octet it requires four electrons. Oxygen requires only two electrons in the outer shell. Therefore electron-dot structure will be :

Every oxygen atom is joined to carbon atom by double bond.

Question 2.
What would be the electron-dot structure of a molecule of sulphur which is made up of eight atoms of sulphur? (HINT. The eight atoms of sulphur are joined together in the form of ring.)
Answer:
The atomic number of sulphur is 16

Sulphur has 6 electrons in the outermost shell and to complete an octet it requires 2 electrons.
∴ Sulphur atom will share 2 electrons. It’s chemical formula is S₈.

Question 3.
How many structural isomers can you draw for pentane?
Answer:
Three ; n-Pentane, iso-pentane, neo-pentane.
Structural isomers can be drawn for pentane.

Question 4.
What are the two properties of carbon which lead to the huge number of carbon compounds we see around us?
Answer:

1. Catenation: The carbon atoms have an astonishing property to combine and form bond with other carbon atoms to form long chain compounds. This property is known as catenation. In this, either long chain of carbon are in ring form or the carbon atoms join in single, double or triple bond.
2. Tetravalency: Carbon has four electrons in the outermost shell. That is why its valency is four and it has got capacity to make bonds with other elements. Oxygen, Hydrogen, Nitrogen, Sulphur, Chlorine and many other elements can make new compounds with the help of carbon.

Question 5.
What will be the formula and electron dot structure of cyclopentane?
Answer:
Molecular formula of cyclopentane = C₅ H_{2 × 5} = C₅H₁₀

Question 6.
Draw the structures for following compounds :
Are structural isomers possible for bromopentane?
(i) Ethanoic acid
Answer:
Ethanoic acid (CH₃COOH)

(ii) Bromopentane
Answer:

Due to exchange of position of carbon with bromine, many isomers of bromopentane are possible.
For example :

(iii) Butanone
Answer:

(iv) Hexanal.
Answer:

Question 7.
How would you name the following compounds?
(i) CH₃ – CH₂ – Br
Answer:
Bromoethane

Answer:
Methanal

Answer:
Hex-1-yne.

Question 8.
Why is the conversion of ethanol to ethanoic acid an oxidation reaction?
Answer:
This is because in this reaction oxygen gets added to ethanol.

Question 9.
A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
Answer:
A mixture of ethyne and air is not burnt for welding. This is because air also contains nitrogen along with oxygen. Nitrogen will also burn in oxygen producing oxides of nitrogen such as nitre oxide (NO) and nitrogen dioxide (NO₂) which cause pollution.

Question 10.
How would you distinguish experimentally between an alcohol and a carboxylic acid?
Answer:
The following two tests are used :

• Litmus test: Treat the given compound with blue litmus solutions. If the blue litmus solution turns red, it is a carboxylic acid and if does not turn red, it is an alcohol.
• Sodium bicarbonate test: Add some sodium bicarbonate solution to the given compound. If their is a brisk evolution of a colourless and odourless gas (CO₂) which turns freshly prepared lime water milk, it is carboxylic acid and if their is no effervescence, it is an alcohol.

Question 11.
What are oxidising agents?
Answer:

• The substances which can oxidise other substances by giving oxygen are called oxidising agents.
• Examples: Alkaline potassium permanganate solution, acidified potassium dichromate solution, etc.

Question 12.
Would you be able to check if water is hard using a detergent?
Answer:
No, we can’t check whether the water is hand or soft using a detergent.

Question 13.
People use a variety of methods to wash clothes. Usually after adding the soap, they ‘beat’ the clothes on a stone, or beat it with a paddle, scrub with a brush, or the mixture is agitated necessary to get clean clothes?
Answer:
This is because when soap molecules dissolve in the dirt, the dirt is somewhat loosened from the clothes, and in order to remove it from clothes, the clothes have to be beaten on a stone or beaten with a paddle or scrubbed with a brush or mixture has to be agitated in washing machines.

Punjab State Board PSEB 9th Class Science Important Questions Chapter 5 The Fundamental Unit of Life Important Questions and Answers.

PSEB Solutions for Class 9 Science Chapter 5 The Fundamental Unit of Life

PSEB 9th Class Science Guide The Fundamental Unit of Life Textbook Questions and Answers

Question 1.
Make a comparison to write down ways in which plant cells are different from animal cell.
Answer:

Features	Plant Cell	Animal Cell
1. Cell wall	Cell wall is formed of cellulose.	Cell wall is absent.
2. Centrosome	Absent.	Present.
3. Vacuoles	Large-sized and many present, small-sized.	Generally absent but if only a few.
4. Plastids	Present.	Absent.
5. Reserve food	In the form of starch and paramylon.	In the form of glycogen
6. Nucleus	Central.	Acentric away from centre.

Question 2.
How is prokaryotic cell different from a eukaryotic cell?
Answer:
Differences between prokaryotic cell and eukaryotic cell

Prokaryotic cell

Eukaryotic cell

1. Found in Bacteria, blue-green algae and , Mycoplasma. 2. Primitive nucleus called nucleoid present. Chromosome is single, circular and double-stranded DNA but no proteins (so naked), No nuclear membrane. 3. Cell wall when present, it is formed of peptidoglycan. 4. Membrane-bound Cell-organelles like mitochondria, plastids, E.R., golgi bodies etc. is absent. 5. Ribosomes are of 70 S type. 6. Small-sized (1 – 10 um). 7. Cell division by fission or budding.

Found in Protista, Fungi, Plantae and Animalia. 2. A true nucleus present. Chromosomes are two to man, linear and formed of DNA and histones. Nuclear membrane present. 3. Cell wall when present in plant cells it is formed of cellulose. 4. Membrane-bound Cell-organelles like mitochondria, plastids, E.R., golgi bodies etc. is present. 5. Ribosomes are of 80 S type. 6. Large-sized (5 – 100 /un). 7. Cell division bv mitosis and meiosis.

Question 3.
What would happen if a plasma membrane ruptures or breaks down?
Answer:
Plasma membrane maintains the shape and protects the organelles. If it gets ruptured the internal organisation will be lost and it will not be able to perform its function. Then cell wall die and contents of cell will get disintegrated.

Question 4.
What would happen to the life of a cell if there was no Golgi apparatus?
Answer:
1. The Golgi apparatus performs the function of storage, modification and packaging of materials synthesised in the cell. These materials will not be able to perform their function in its original form.
2. The formation of lysosomes will be affected.

Question 5.
Which organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondria are known as ‘power house’ of the cell. They are sites for synthesis, storage and transport of ATP (Adenosine triphosphate) commonly called energy currency.

Question 6.
Where do the lipids and proteins constituting the cell membrane get synthesised?
Answer:

• Proteins are synthesised bv ribosomes.
• SER is site for synthesis of lipid.
• These proteins and lipids are modified by golgi apparatus to form plasma membrane.

Question 7.
How does an Amoeba obtain its food?
Answer:
Plasma membrane is flexible and it enables the cell to engulf in food and other materials from the external environment. Such a process is termed endocytosis.

Question 8.
What is osmosis?
Answer:
Osmosis. It is a special case of diffusion of water through a selectively permeable membrane. It is a passage of water from a region of higher concentration through a semi- permeable membrane to a region of low water concentration.

Question 9.
Carry out the following osmosis experiment:
Take four peeled potato halves and hollow each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,
(a) keep cup A empty
(b) put one teaspoon sugar in cup B
(c) put one teaspoon salt in cup C
(d) put one teaspoon sugar in the boiled potato cup D.
Keep this setup for two hours. Then observe the four potato cups and answer the following.
1. Explain why water gathers in the hollowed portion of B and C.
2. Why is potato A necessary for this experiment?
3. Explain why water does not gather in the hollowed out portions of A and D?
Answer:
1. The water gathers in hollowed portion of potato cups B and C due to osmosis.
2. Cup A acts as control experiment and indicates that cavity of potato will not induce any type of movement.
3. Cup A does not contain hypertonic solution hence water does not rise. In cup D, cells of potato cup being boiled cells are dead and no osmosis occurs.

Science Guide for Class 9 PSEB The Fundamental Unit of Life InText Questions and Answers

Question 1.
Who discovered cell and how?
Answer:
Robert Hooke (1665) discovered cell for the first time. He examined a thin slice of cork under the microscope. He observed that cork resembled the structure of a honey comb consisting of many hexagonal compartments and called these boxes ‘cells’.

Question 2.
Why is cell called the structural and functional unit of life?
Answer:

1. Cells are arranged in proper and systematic order to form a body of living organism. Thus cells serve as basic building structural units for more complex organisms.
2. Cell is also functional unit of life because all the metabolic activities of life take place at cell level.
3. Respiration, digestion, excretion and reproduction occur at cell level.
4. Cells contain genetic material which regulate cell functions and pass on all information to the next generation.

Question 3.
How do substances like C0₂ and water move in and out of the cell? Discuss.
Answer:
The substances like C0₂ and water move in and out of cell by the process of diffusion. There is spontaneous movement of substances from higher concentration to lower concentration. The movement of water across selectively permeable membrane is called osmosis.

Question 4.
Why is the plasma membrane called selectively permeable membrane?
Answer
Plasma membrane permits the entry and exit of selected materials in and out of the cell. It also prevents movement of some materials required within the cell. The membrane is called selectively permeable membrane.

Question 5.
Fill in the gaps in the following table illustrating differences between prokaryotic and eukaryotic cells.

Prokaryotic Cell	Eukaryotic Cell
1. Size: generally small (1 – 10 µm) = 10-6m 2. Nuclear region ……………. and known as ……………….. 3. Chromosome single. 4. Membrane-bound cell organelles absent.	1. Size: generally large 5 – 100 µm 2. Nuclear region well defined and surrounded by a nuclear membrane. 3. More than one. 4. ………………………………………………..

Answer:
2. Nuclear region undefined due to absence of nuclear membrane and known as Nucleoid.
4. Membrane-bound cell organelles such as mitochondria, Golgi bodies, chloroplast, etc. are present.

Question 6.
Can you name two organelles we have studied that contain their own genetic material?
Answer:

• Chloroplasts
• Mitochondria.

Question 7.
If the organization of the cell is destroyed due to some physical or chemical influence, what will happen?
Answer:
Each cell has certain special cell organelles. Each performs a special function. If an organization is destroyed cell will stop performing basic functions and result in its death.

Question 8.
Why are lysosomes called ‘suicidal bags’?
Answer:
Lysosomes are membrane-bound sacs filled with enzymes and this enzyme may digest their own contents if burst. They carry out autolysis (auto = self; lysis = break down) hence called “suicidal bags.”

Question 9.
Where are proteins synthesized inside the cell?
Answer:
Proteins are synthesized on the ribosomes which are attached to the surface of RER or lie freely in the cytoplasm. Ribosomes are also called “protein factories” of cells.

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 6 Life Processes Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 6 Life Processes

PSEB 10th Class Science Guide Life Processes Textbook Questions and Answers

Question 1.
The kidneys in human beings are a part of the system for :
(a) nutrition
(b) respiration
(c) excretion
(d) transportation.
Answer:
(c) excretion.

Question 2.
The xylem in plants are responsible for :
(a) transport of water
(b) transport of food
(c) transport of amino acids
(d) transport of oxygen.
Answer:
(a) transport of water.

Question 3.
The autotrophic mode of nutrition requires :
(a) CO₂ and water
(b) Chlorophyll
(c) Sunlight
(d) All of the above.
Answer:
(d) All of above.

Question 4.
The breakdown of pyruvate to give CO₂, water and energy takes place in :
(a) cytoplasm
(b) mitochondria
(c) chloroplast
(d) nucleus
Answer:
(b) mitochondria.

Question 5.
How are fats digested in our bodies? Where does the process take place?
Answer:
Digestion of fats takes place in the intestine. The fats are emulsified by the bile salts present in bile. The emulsified fats are acted upon by pancreatic lipase (strepsin) which hydrolyses fats into fatty acids and glycerol. The intestinal lipase also hydrolyses the emulsified fats into fatty acids and glycerol.

Question 6.
What is the role of saliva in the digestion of food?
Answer:
Role of saliva

• Saliva lubricates the food and facilitates mastication.
• Saliva binds the food molecules together.
• Saliva contains ptyalin (salivary amylase) enzyme which acts on starch, glycogen and other carbohydrates to form maltose.

Question 7.
What are the necessary conditions for autotrophic nutrition and what are its byproducts?
Answer:
Photosynthesis is essential in case of autotrophic nutrition

Conditions required for photosynthesis

• CO₂ is necessary for photosynthesis.
• Water is required.
• Sunlight is necessary for photosynthesis.
• Chlorophyll is essential for photosynthesis.
• By-products. Molecular oxygen is liberated as a byproduct.

Question 8.
What are the differences between aerobic respiration and anaerobic respiration? Name some organisms that use anaerobic mode of respiration.
Answer:
(a) Differences between aerobic and anaerobic respiration

Aerobic respiration	Anaerobic respiration
1. It takes place in the presence of oxygen.	1. It takes place in the absence of oxygen.
2. It is completed in cytoplasm and mitochondria of cells.	2. It is completed in the cytoplasm only.
3. It involves the complete oxidation of glucose into CO2 and H2O and a large amount of energy is released.	3. It involves the incomplete oxidation of glucose into CO2 and alcohol or lactic acid and less amount of energy is released.
4. The process is harmless.	4. It is toxic to plants.

(b) Anaerobic respiration takes place in bacteria and yeast.

Question 9.
How are alveoli designed to maximise the exchange of gases?
Answer:

Question 10.
What would be the consequences of a deficiency of haemoglobin in our bodies?
Answer:
Haemoglobin is a respiratory pigment present in RBC of blood. It has high affinity for oxygen. One molecule of haemoglobin carries 4 molecules of oxygen. If simple diffusion were to move oxygen in our body, it is estimated that it would take 3 years for a molecule of oxygen to reach tip of toes from lungs.

Question 11.
Describe double circulation in human beings. Why is it necessary?
Answer:
Double circulation. In human beings heart is four-chambered, having right and left auricles and right and left ventricles. The right auricle receives the deoxygenated blood from the body and sends it into the right ventricle that pumps it to the lungs via a pulmonary arch for oxygenation. The left auricle receives oxygenated blood from the lungs and sends it into the left ventricle, which pumps it to the body through a single aortic arch.

Significance:

• Thus, the deoxygenated and oxygenated blood remain fully separate, and there is complete double circulation.
• It increases efficiency.

Double circulation of blood in birds and mammals.

Question 12.
What are the differences between the transport of materials in xylem and phloem?
Answer:
Differences between transport in xylem and phloem

Transport in xylem	Transport in phloem
1. Water and minerals are transported through xylem.	1. Sucrose, amino acids and other substances are transported through phloem.
2. Xylem helps in upward movement, i.e. from roots to stem, branches and leaves.	2. Phloem is responsible for downward and lateral movement from leaves to other parts.

Question 13.
Compare the functioning of alveoli in the lungs and nephrons in the kidneys with respect to their structure and functioning.
Answer:

• Alveoli of lungs remove CO₂ as a waste during exchange of gases and nephrons filter wastes from blood.
• Alveoli are supplied with extensive network of blood capillaries for gaseous exchange. Bowman’s capsule surrounds a cluster of capillaries for filtration.
• Both increases surface area either for gaseous exchange or filtration.
• Urea and uric acid wastes are removed in the nephron.
• Both purify blood lungs alveoli by removing waste gases and nephrons by filtering the waste products in the form of urine.

Science Guide for Class 10 PSEB Life Processes InText Questions and Answers

Question 1.
Why is diffusion insufficient to meet the energy requirements of multicellular organisms like humans?
Answer:
In multicellular organisms, all the cells of body may not be in direct contact with the surrounding source of oxygen i.e. environment, thus simple diffusion will not meet the oxygen requirements of all the cells. These organisms require specialised organs to meet the oxygen requirement.

Question 2.
What criteria do we use to decide whether something is alive?
Answer:
Features of living organisms

• Movements
• Growth
• Metabolism
• Cellular body
• Nutrition
• Respiration
• Transportation
• Excretion
• Respond to stimuli
• Reproduction.

Question 3.
What are outside raw materials used by living organism?
Answer:
Outside raw materials used by living organism

• Energy obtained from food.
• Oxygen: Required for breaking down of carbon based molecules to liberate energy in the body.
• Water: It is required for proper digestion of food and other functions in the body. It is raw material for photosynthesis in plants. All reactions occur in solution form in the body.
• CO₂ Raw material for photosynthesis in plants. All reactions occur in solution form in the body.

Question 4.
What processes would you consider essential for maintaining life?
Answer:

• Nutrition
• Respiration
• Transportation
• Excretion.

Question 5.
What are the differences between autotrophic and heterotrophic nutrition?
Answer:
Differences between Autotrophic and Heterotrophic nutrition

Autotrophic Nutrition	Heterotrophic Nutrition
1. It occurs in green plants and blue green algae.	1. It occurs in animals and insectivorous plants.
2. CO2 and water are raw materials which combine to form organic compound.	2. They depend on plants and herbivore for their food.
3. They need chlorophyll and sunlight	3. There is no need of chlorophyll and sunlight,

Question 6.
Where do the plants get each of raw materials required for photosynthesis? (PB. Board 2011)
Answer:
Raw materials of photosynthesis

• CO₂
• Water.
• Nitrogen

1. CO₂ is obtained from air. It enters the leaf through stomatal openings.
2. Water is obtained from soil. It enters the leaf through the mid-rib and vein from the root which absorbs it from the soil.
3. Nitrogen: It is obtained from soil.

Question 7.
What is the role of acid in our stomach?
Answer:
HCl is obtained from gastric glands present in the wall of the stomach.

Functions of HCl:

• It provides acidic medium. It is required for the action of enzymes. It changes the pH of food from almost neutral to acidic medium (from pH 7 to 2)
• Activates the inactive proenzyme propepsin into active pepsin.
• Kills the bacteria present in food.
• It softens calcium.
• It regulates the opening and closing of the pyloric aperture.

Question 8.
What is the function of digestive enzymes?
Answer:
Role of digestive enzymes: These enzymes convert the complex non-diffusible form of food into simple diffusible form.

• Ptyalin converts starch into maltose.
• Pepsin breaks down proteins into peptides and amino acids.
• Rennin curdles milk protiens so that they can stay for longer period to be acted upon by pepsin.
• Lipase acts on fats and forms fatty acid and glycerol.
• Maltase acts on maltose and forms glucose.

Question 9.
How is small intestine designed to absorb digested food?
Answer:
Small intestine is a long tubular structure. The inner wall of small intestine is thrown into folds called villi. The absorptive cells have numerous finger-like processes called microvilli. They increase the surface area for absorption of food. These villi have blood vessels named lacteals from absorption of food.

Question 10.
What advantage over an aquatic organism does a terrestrial organism have with regard to obtaining oxygen for respiration?
Answer:
The amount of oxygen dissolved in water is very low as compared to the amount of oxygen in air. Thus these organisms have to make less efforts to obtain oxygen.

Question 11.
What are the different ways in which glucose is oxidised to provide energy in various organisms?
Answer:
Different pathways to provide energy from glucose

Question 12.
How is oxygen and CO₂ transported in human beings?
Answer:
1. Transport of oxygen: It is transported from respiratory organs to body cells,
1. Haemoglobin helps in the transport of oxygen. In the alveoli of the lungs, the haemoglobin (Hb) present in red blood corpuscles combines with oxygen to form oxyhaemoglobin. When the blood reaches the tissue, oxygen is released from the oxyhaemoglobin for the consumption by the tissues.
Hb + O₂ → HbO₂

2. Some of O₂ is transported in the solution form by plasma of blood.

2. Transport of CO₂

• CO₂ diffuses into blood plasma to form physical solution.
• CO₂ forms unstable carbonic acid with water and is transported as such.
• CO₂ is also transported from tissue to lungs as bicarbonates.

Question 13.
How are lungs designed in human beings to maximise the area for exchange of gases?
Answer:
Within the lungs, the primary bronchi divides into smaller and smaller tubes which finally terminate into balloon-like structures called alveoli. These alveoli increase the surface area for exchange of gases. There are 750 million alveoli in the lungs of man. If the alveolar surface is spread out it would cover about 80 m2. Thus it makes efficient exchange of gases.

Each alveolus or air sac has a diameter of 75 to 300 microns and has a very thin wall. The walls of the alveoli are elastic and are supplied with capillaries. Through these thin walls gases are exchanged between the capillaries and the air sacs.

Question 14.
What are the components of the transport system in human beings? What are the functions of these components?
Answer:
There are two main transport systems in human beings :

1. Blood vascular system.
2. Lymphatic system.

Components of blood vascular system

• Blood: It is a reddish viscous fluid connective tissue. In an adult human being, it is 5-6 litres in amount. Blood consists of two parts – plasma and formed elements. (RBCs, WBCs and blood platelets). Blood transports digested food, oxygen, carbon dioxide, nitrogenous wastes and hormones in the body.
• Heart: It is a hollow, muscular pumping organ. The heart sends the blood to lungs. Heart pumps the blood in the body.
• Blood vessels: The blood vessels which carry oxygenated blood are called arteries. They divide to form capillaries of finer dimensions. Exchange of materials takes place across the capillaries. It is possible because the walls of capillaries are extremely thin. The blood from the tissues is returned by veins.

Components of Lymphatic system

1. Lymph: It acts as middle man between blood and tissue. It destroys harmful bacteria
2. Lymph vessels
3. Lymph capillaries
4. Lymph nodes

Question 15.
Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Answer:

• In the heart of these organisms the left side has oxygenated blood and right side deoxygenated blood.
• The separation of blood allows a highly efficient supply of oxygen to the body.
• It is essential for such animals which have high energy needs.
• They also constantly use energy for maintaining body heat.

Question 16.
What are the components of transport system in highly organised plants?
Answer:
Components of transport system in plants

• Xylem tissue. Vessels and tracheids of roots, stems and leaves are concerned with transport of water and minerals in plants.
• Phloem consists of sieve tubes and companion cells. It transports food, amino acid, phytohormones and other substances from leaves to various parts of plants.

Question 17.
How are water and minerals transported in plants?
Answer:
Transport of water and minerals
1. In xylem tissue, vessels and tracheids of the roots, stems and leaves are interconnected to form a continuous system of water conducting channels reaching all parts of the plants.

2. Plants absorb water and minerals through their entire surface i.e., roots, stem and leaves. However, mainly the water is absorbed by roots from soil.

3. The area of young roots where most of the absorption takes place is the root hair zone.

4. This zone is the area of greatest permeability.

5. Passage of water in root or pathway of water in root

• The entry of water into the root hair dilutes the cell sap. Thus water molecules in root hair increase as compared to adjacent cortical cells.
• Water reaches the passage cells of endodermis. These passage cells lie opposite the xylem.
• They allow water to entre the pericycle.
• So, water enters the xylem from pericycle for upward movement of sap.

6. The Ascent of Sap:
The upward movement of water from the root towards the top of the plant in the xylem vessels is called ascent of sap. The upward transport of water and minerals in plants which are in some cases as tall as 400 ft. poses a serious problem.

7. Transpiration also helps in the absorption and upward movement of water and minerals dissolved in it from roots to the leaves.

Question 18.
How is food transported in plants?
Answer:
Transport of food in plants:
The food prepared in the green leaves of plants is transported through phloem in the form of sucrose solution to storage organs of roots, seeds and fruits. This process is called translocation. This process requires energy. It is provided by ATP molecules. This increases the osmotic pressure in the tissue causing water to move into it. This pressure moves the material in the phloem to tissues which have less pressure.

Question 19.
Describe the structure and functioning of nephron.
Or
How does urine formation occur in human?
Answer:
Structure of a Nephron:
A nephron is made up of:

• a globular double-walled Bowman’s capsule around a clump of capillaries or glomerulus, and
• a tubule surrounded by blood capillaries.

The tubule consists of
(a) a proximal convoluted portion
(b) the loop of Henle, with descending and ascending limbs, and
(c) a distal convoluted part.

The nephron empties into a collecting duct. The two million nephrons of a human being, end to end would extend for nearly 80 km. All the collecting ducts discharge into a central cavity of the kidney (pelvis) that connects to the ureter.

Functioning of Nephron
Urine is formed by 3 processes: glomerular filtration, tubular reabsorption and tubular secretion in the nephrons of the kidney.
1. Ultrafiltration (Glomerular filtration):
Blood is filtered under pressure in the glomeruli present in the cup-like structure of Bowman’s capsule. Glomerular (nephric) filtrate is formed.

Nephron and its function

2. Tubular reabsorption:
In the PCT, entire glucose, amino acids, vitamins and hormones, most of the inorganic ions are reabsorbed by active transport, most of water by osmosis, and some urea by back diffusion from nephric filtrate.
Loop of Henle mainly concentrates urine to conserve water. Here, some inorganic ions are actively taken up and some water leaves by osmosis.

3. Tubular secretion:
In the DCT, collecting tubule and collecting duct, many ions, water (depending upon availability) are secreted in to DCT and collecting duct.
Urine formed passes into bladder from kidney through ureters.

Question 20.
What are the methods used by plants to get rid of excretory products?
Answer:
Excretory products of plants include CO₂, salts, resins, tanins latex etc. Excretion in Plants

• Excess of water passes out during transpiration.
• Plants get rid of dead tissue as a measure to eliminate waste.
• Waste products may be stored in cellular vacuoles.
• Waste products may be stored in leaves which fall off.
• Resins and gums are stored in old xylem.
• Plants also excrete wastes into soil.
• Aquatic plants lose their waste products by diffusion into the water.

Question 21.
How is the amount of urine produced regulated?
Answer:

• Amount of urine formed depends upon the availability of water in the body.
• ADH (Antidiuretic Hormone) regulate the amount of water.
• Osmoregulation helps in regulation of salts and water.
• Urine is stored in urinary bladder.

Punjab State Board PSEB 10th Class Science Important Questions Chapter 3 Metals and Non-metals Important Questions and Answers.

PSEB 10th Class Science Important Questions Chapter 3 Metals and Non-metals

Long Answer Typt Questions

Question 1.
Show various steps involved in extraction of metal from an ore by a sketch.
Answer:

Steps involved in the extraction of metals from ores.

Question 2.
Give methods of enrichment of ores.
Answer:
Methods of enrichment of ores. Ores or minerals are mined from earth these are usually contaminated with large amount of impurities which are called gangue. It is necessary to remove these impurities before extraction of metals. By removing gangue the ore is enriched and concentration of metal is increased. Therefore ore in enriched prior to other processes. Methods of removing gangue from ore depends on the difference of physical and chemical properties of both of them.

Enrichment of ore using magnetic method.

Physical methods of enrichment :

• Hydraulic Washing: In this method finely powdered ore is washed with jet of water. In this strong flow of water light gangue particles are washed away where as heavy ore particles settle down, Tin and lead ores are enriched by this method.
• Froth Floatation Method: In this method, mixture of powdered ore and water or some appropriate oil is taken in a tank. Ore particles are coated with oil and gangue particles are wet with water. A blast of compressed air is blown through the pipe of a rotating agitation to produce froth, due to this, mineral particles wetted with oil change into foam and float on the surface of water. Froth containing ore particles is easily transferred to another container sulphides of copper, lead and zinc are enriched by this method.

Chemical Methods: The chemical method used for the concentration of the ore is based on the difference in some chemical property of the metal and the impurities. An example of this method is the concentration of bauxite ore of aluminium.

Concentration of aluminium ore by Bayer’s process: In this method, Bauxite is reduced by treating it with hot sodium hydroxide. It gives sodium meta aluminate (NaAlO₂) which is soluble in water. The solution in filtered to remove the gangue present in the ore because it does not dissolve in sodium hydroxide. NaAlO₂ is allowed to react with hydrochloric acid to obtain Aluminium hydroxide. On strong heating aluminium hydroxide pure aluminium oxide is obtained.

Following reactions take place

Question 3.
Explain General methods used in the extraction of metals.
Answer:
Steps involved in the extraction of metals :

• Enrichment (concentration) of ore.
• Converting concentrated ore into oxide.
• Reduction of metal oxide to obtain metal.
• Refining of impure metal.

1. Concentration :
(A) Hydraulic washing: This method is used for concentration of oxide ores Gangue particles are lighter as compared to ore particles. In this method powdered ore is washed with flowing water. Light gangue particles are washed away with water and heavy ore particles are left.

(B) Froth floatation method: In this method powdered ore is taken in a tank containing water pine oil is also added to it. Sulphide ore is wet with oil and gangue is wet with water.

The water is agitated by blowing compressed air violently, a froth is formed on the surface of water. This froth carries the lighter ore particles along with it to the surface. Gangue particles are heavy and settle to the bottom.

(C) Magnetic separation.

Enrichment of ore using magnetic method.

1. Magnetic method: This method is acceptable for magnetic impurities like iron, cobalt, Nickel etc. Minerals which are of magnetic nature got attracted towards magnetic field. Chromite and pyrolusite ores are enriched by this method. In this method ground ore is placed on a conveyer belt. This belt goes around two rollers one of which is magnetic. When ore comes near the magnetic roller then two heaps of magnetic and non magnetic materials are obtained. Iron ore magnetite is enriched by this method.

(D) Chemical separation: This process is based on the difference between chemical – properties of ores and gangue eg. Bauxite Al₂O₃.2H₂O is impure form of aluminium oxide. It contains Iron (III) oxide (Fe₂O₃) and sand (SiO₂) as main impurities. Due to iron (III) oxide its colour is red brown. Bayer’s process is used to obtain pure aluminium from / bauxite. In this methods powdered ore is mixed with heated sodium hydroxide.
Al₂O₃ (S) + 2NaOH (aq) → 2NaAlO₂ (aq) + H₂O (l)
NaAlO₂ (aq) + 2H₂O (l) → Al(OH)₂ (s) + NaOH (aq)

2. Converting concentrated ore into metal oxide
Roasting: In this process ore is heated in the presence of air to obtain metal oxide. Which can easily be reduced to obtain the metal.

Zinc blende contains zinc sulphide when concentrated zinc blende ore (zinc sulphide) is roasted in air then it gets oxidized to give zinc oxide.

Calcination: In this process ore is heated in the absence of air to remove moisture and volatile impurities.
When carbonate ore is heated it dissociates to give metal oxide.

3. Extracting metals from metal oxide.
To obtain metal from metal oxide it is heated with some reducing agent. To obtain metals zinc, iron, tin etc. their oxides ore heated with carbon which acts as reducing agent.
ZnO(s) + C(s) → Zn(s) + CO(g)

Oxides of metals with medium activity can be reduced by using highly reactive metals like sodium, calcium and aluminium etc.
3MnO₂(s) + 4Al(s) → 3Mn(l) + 2Al₂O₃(s) + heat

4. Electrolytic refining.
In this method impure metal is taken as anode and a thin strip of pure metal is taken in the form of cathode metal salt solution is taken as electrolyte. When electric current is passed through the electrolyte, pure metal from anode dissolves into solution and impurities settle down as anode mud.

Electrolytic refining

Question 4.
(a). How do metals and non-metals react?
Answer:
Metals and non-metals react on the basis of electronic configuration in the valence shell.

Sodium has only one electron in its outer most shell. If it lose its electrons of the M shell then L will become its outermost shell which have complete octet. Nucleus of this atom will have 11 protons but number of electrons is 10, therefore it is positively charged and gives Na+ sodium positive ions. On the other side, there are 7 electrons in the outer most shell of chlorine and it requires one electron to complete its octet. If there is reaction between chlorine and sodium then lost electron of sodium atom is gained by chlorine atom and chlorine atom becomes negatively charged by one unit. Because there are 17 protons in the nucleus of the chlorine atom and there are 18 electrons in K, L and M shells. Therefore, chloride negative ions Cl- is obtained.

Due to opposite charges sodium and chloride ions attract each other and they form strong bonds involving electrostatic forces and form sodium chloride.

Another ionic compound, magnesium chloride is shown in fig.
Formation of NaCl and MgCl₂ by Electron transfer :

Formation of sodium chloride.

Formation of sodium chloride.

Compounds formed by metals and Non-Metals by the transfer of electrons between them are called ionic or electrovalent compounds.

(b) Write four main exceptions from normal properties of metals and Non-Metals.
Answer:

• All the metals are solid at room temperature except mercury. Melting point of metal is usually high but of Gallium and Cesium is low.
• Iodine is a non-metal but still shiny.
• Carbon is a non-metal which can have many forms. Diamond is allotrope of carbon. It is the hardest substance found in nature. Its melting and boiling point are very high. Another allotrope of carbon is graphite which is conductor of electricity.
• Alkali metal (lithium, sodium, Potassium) are so soft that these can be cut by knife. They have low density and low melting point.

Question 5.
How will you differentiate between metals and non-metals?
Answer:
Differences between metals and non-metals on the basis of physical properties :

Metals	Non-metals
1.         All metals are solid at room temperature. But mercury is liquid at room temperature.	1. Non-metals exist in all the three states at room temperature. Phosphorous and sulphur are solid, H2, O2, N2 in gaseous state, and bromine in liquid state.
2. Metals are ductile, malleable and tenacious.	2. These are soft.
3. Metals have lustre i.e. metal shine.	3. They do not have lustre but diamond, graphite and iodine are exceptions.
4. Metals are good conductors of heat and electricity but bismuth is exception.	4.All non metals are non conductors except graphite and carbon gas.
5. Metals have high melting and boiling points.	5. Non metals have low melting and boiling points.
6. Metals are hard but sodium and potassium can be cut by knife.	6. These are not very hard but diamond is the hardest substance.
7. Metals have very high relative densities but Na, K are exceptions.	7. Non metals have very low relative densities.
8. Metals are opaque.	8. Gaseous non metals are transparent.

Difference between metals and non-metals on the basis of chemical properties

Metals	Non-metals
1. Metals form alkaline oxides some of them form bases.	1. Non-metals form acidic or neutral oxides.
2. Metals react with acids to displace hydrogen and form salts.	2. Non-metals do not displaces hydrogen from acids.
3. Metals are electropositive in nature.	3. Non-metals are electronegative in nature.
4. Metals combine with chlorine to form chlorides which are electrovalent compounds.	4. Non-metals combine with chlorine to form chlorides which are covalent compounds.
5. Some metals combine with hydrogen to form hydrides which are electrovalent.	5. Non-metals combine with hydrogen to form hydrides which are covalent.
6. Metals are reducing agents.	6. Non-metals are oxidizing agents.
7. Metals form positive ions in aqueous solution.	7. Non-metals form negative ions in aqueous solution.

Question 6.
Discuss about the extraction of metals
Answer:
Some metals are found in free state in nature. Some metals are found in the form of compounds. Metals at the bottom of reactivity series show very low reactivity. These are found in free state. Gold, silver, platinum and copper are found in free state.

Copper and silver are also found in the form of sulphide and oxide ores. Metals (K, Na, Ca, Mg and Al) which are at the top of reactivity series show very high reactivity that they are never found in free state. Metals at the middle of the reactivity series (Zn, Fe, Pb etc.) are moderately reactive. These are found in the form of oxide, sulphide or carbonate. Some metal ores are found in the form of oxides.

Metals are classified into three types:
(a) least reactive metals
(b) Moderately reactive metals
(c) highly reactive metals.

Reactivity series and metallurgy

Question 7.
What is rust? What are the requirements necessary for its completion? Give ways to prevent rusting of iron?
Answer:
Surface of iron aquires a coating of a brown flaky substance called rust. It is a compound of Iron (III) Oxide and iron (III) hydroxide. It weakens the iron surface. Due to this, a great loss occurs to the iron articles.

The presence of moisture and air is necessary for rusting of iron. This can be proved with an experiment. If we take new shining irons nails in three test tubes as shown, then we find that nails which are in contact with water and air, got rusted. If we completely immerse the nails in water and cover the water surface with oil so that there is no air available for the nails, then nails will not get rusted.

Similarly if we use CaCl, in the test tube absorbs all the moisture so that no moisture is available in this case also, nails will not get rusted.

Ways to Prevent Rusting :

1. Using oil or grease on the surface: If iron surface is covered with oil or grease it does not remain in contact with air and thus rusting is prevented. Machine parts are saved by this method.
2. Using enamel: By painting iron surface, rusting can be prevented. Buses, cars, scooter, motor cycle, windows, trains etc. are saved by this method.
3. Covering with plastic: Iron surface is covered with plastic. Iron furniture is saved by this method.
4. Galvanization: A process of coating thin layer of zinc on iron is called galvanization. This method is used to prevent buckets, tubs, drums, iron sheets etc. from rusting.
5. By electroplating: Iron can be electroplated by metals like Nickle, Chromium, aluminium etc. Rims, handles, bumpers etc. of vehicles are prevented from rusting by this method.
6. By tin: Iron is coated with tin. Ghee canisters, boxes used for packing food are tinned.
7. Converting to steel: Iron can be preverted from rusting by converting it into steel.

Question 8.
Explain General properties of ionic compounds.
Answer:
General properties of ionic compounds are given below:

• Physical nature: Due to strong force of attraction between positive ions and negative ions, ionic compounds are solid. They are brittle and break on pressing.
• Melting and boiling point: They have high melting and boiling points. Because a large amount of energy is required to break the strong inter ionic attraction.
• Solubility: Ionic compounds are normally soluble in water but are insoluble in Kerosene, Petrol etc.
• Electric Conductivity: In solid form ionic compounds do not conduct electricity because of strong and firm structure. Movement of ions is not possible. But ionic compounds can conduct electricity in molten state, because electrostatic force of attraction becomes very weak due to heat energy. Therefore ions can move freely and electric current can pass through it. Mobility of charged particles is necessary for conduction of electricity in a solution. Ions are present in aqueous solution of ionic compounds. When electric current is passed through the solution then ions start moving towards the opposite electrodes.

Question 9.
What is an alloy? Magnetic iron oxide explain the objective of their formation?
Answer:
Alloy: An alloy is a homogeneous mixture of a metal with another metal or non-metal, e.g. solder is an alloy of lead and tin (Pb and Sn). Stainless steel, solder, brass, bronze, bell metal etc.

Uses of alloys :

• For increasing hardness: Iron is mixed with carbon to form stainless steel which is harder than iron. Copper is mixed with gold and lead is mixed with silver to make them hard. Duralium is an alloy made from aluminium and is very hard.
• Increasing strength: Steel, Duralium are hard as well as strong.
• Preventing Corrosion: By making stainless steel an alloy of iron, which do not get rusted.
• To produce sound: Bell metal is an alloy of copper and tin used to produce loud sound.
• To lower melting point: An alloy of Bismuth, tin and lead has low melting point.
• Moulding: Bronze and type metal.
• For change in colour: Aluminium bronze is an alloy of copper and aluminium is of golden colour.
• Domestic uses: Alloys are used in homes, factories, offices etc. e.g. utensils, almirahs, fans, refrigerators elements etc. are made up of alloys.

Question 10.
Explain the activity series of metals.
Answer:
All metals have different rates of activity. Some metals like sodium, potassium and calcium etc. are highly reactive. These metals combine with oxygen to form oxide and react with hydrogen to form hydrides. Some metals are compratively less reactive e.g. iron, zinc etc. Some metals are least reactive e.g. gold, silver. Reactivity of metals depends on their ability to lose electrons, Metals are arranged in a list in decreasing rate of their activity.

Metals which are above hydrogen are more reactive and those below hydrogen are lower in reactivity and are found in free state. In this series potassium is the most reactive metal in this series.

Short Answer Type Questions

Question 1.
Name two metals which are good conductors of heat and electricity. Name metals which are highly and least conducting with reference to heat.
Answer:
Copper and aluminium are good conductors of electricity and heat. Silver is very good conductor of heat whereas lead is not a good conductor of heat.

Question 2.
Define ductility with example.
Answer:
Property of drawing thin wires from a metal is called ductility. Gold is the highest ductile metal. We can draw 2 km long wire from 18 carat gold.

Question 3.
What is electrical conductivity? Name the metals which have the highest conductivity, less than this and the lowest conductivity.
Answer:
It is the ease with which electric current can flow through a metal. Those metals which offer very low resistance to the flow of current they have high conductivity. Silver, copper are very good conductors of current then comes gold, aluminium and tungsten. Lead and iron have least conductivity i.e., they offer very high resistance to the flow of current.

Question 4.
Which property of metals give them characteristic chemical properties?
Answer:
Metals form positive ions by loosing electrons. This property of formation of ions by the metals give them characteristics chemical properties, e.g., Mg form Mg ion by loosing two electrons :
Mg → Mg²⁺ + 2e^–

Question 5.
Ionic compounds are found in which state? Comment on the melting and boiling point of ionic compounds.
Answer:
Compounds which are formed by the transfer of electrons from metals to Non¬Metals are called ionic or electrovalent compounds e.g., NaCl, LiCl, CaCl₂, CaO, MgCl₂. Ionic compounds have very high melting and boiling points because a large amount of energy is required to break the strong inter-ionic attractions.

Question 6.
What is difference between minerals and ores?
Answer:

Sr. No. Minerals	Ores
1. Those natural occuring substances, which contain metals in the form of compounds.	1. These are the minerals from which metals can be extracted easily and cheaply.
2. In many of the minerals percent age amount of metals is large and in some it is less.	2. In all the ores, percentage amount of metals is enough.
3. In some minerals there are so many impurities which create difficulty in the extraction of metals.	3. Ores do not have such problematic impurities.
4. All the minerals can not be used for extracting metals. All the minerals are not ores.	4.         All the ores can be used to extract metals.

Question 7.
How are the metals extracted, which are at the top of reactivity series?
Answer:
Metals which are towards the top of reactivity series are sodium, calcium, magnesium, aluminium. There are very reactive. These metals can not be obtained by heating them with carbon. These have more affinity towards oxygen, therefore these are extracted by electrolytic reduction. Sodium, magnesium and calcium are obtained by the electrolysis of their molten chlorides. Metals got deposited at cathode and chorine is liberated at anode.
At cathode : Na⁺ + e^– → Na
At anode : 2Cl^– → Cl₂ + 2e^–

Aluminium is obtained by the electrolytic reduction of aluminium oxide.
At cathode ; Al³⁺ + 3e^– → Al

Question 8.
How the metals, which are in the middle of the activity series extracted?
Answer:
Metals which are in the middle of the activity series are iron, zinc, lead, copper etc. These are found in the form of sulphides or carbonates. It is easy to obtain metals from their oxides compared to sulphides or carbonates. Therefore before extraction metal sulphide or carbonates are converted into their oxide. Sulphide ores are converted into metal oxides by heating in the presence of air. This is known as roasting. Carbonate ores are heated in limited supply of air to convert them into oxides. This is known as calcination. Following reactions take place during roasting and calcination of zinc.


Then by using carbon as reducing agent, metal is extracted from metal oxide, e.g. when Zinc oxide is heated with carbon it gets reduced to give zinc.

In addition to using carbon for reduction, displacement reaction can be used to extract metals. More reactive metals like sodium, calcium, aluminium etc. can be used as reducing agents because these can displace atoms which are below them in the reactivity series. For example, when mangnese dioxide is heated with aluminium powder then following reaction takes place.

Question 9.
How will you extract metals which are low in the activity series?
Answer:Metals low in the activity series are less reactive and can be obtained from metal oxides simply by heating. Cinnabar (Hgs) an ore of mercury (Hg) when heated change to mercuric oxide (HgO), on heating it further it is reduced to mercury.

Question 10.
Explain the reactions of metals with water.
Answer:
On reacting with water, metals form metal oxide and produce hydrogen. These dissolve in water to form metal hydroxide. But all metals do not react with water.

Metals like sodium and Potassium react with cold water, vigorously. The reaction of sodium and Potassium is very vigorous and exothermic that hydrogen produced starts burning simultaneously.
2K (s) + 2H₂O (l) → 2KOH (aq) + H₂(g) + heat
2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂(g) + heat

Reaction of calcium with water is slow. Heat produced in this reaction is not enough to burn the hydrogen produced in the reaction.
Ca (s) + 2H₂O(l) → Ca (OH)₂ + H₂(g)

Metals like iron, aluminium, zinc etc. do not react with cold water and not even with hot water. But they react with steam to form metal oxide and produce, hydrogen.
2Al(s) + 3H₂O(g) → Al₂O₃(S) + 3H₂(g)
3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
Metals like lead, copper, silver and gold etc. do not react with water.

Question 11.
How do metals react with :
1. Oxygen
2. Dilute acids
3. Chlorine
4. Hydrogen.
Answer:
I. Reaction of metals with oxygen: Metals combine with oxygen to form metal oxides. Metal atoms lose their loosely bound electrons to form positive ions where as oxygen atoms gain electrons to form negative oxide ions. These metal oxide are basic in nature. Since all metals have different level of reactivity therefore they combine with oxygen at different temperatures.
1. Na and K Combine with oxygen at normal temperature to form oxides which dissolve in water to form hydroxide.
4 Na (s) + O₂(g) → 2Na₂S(s)
Na₂O(s) + H₂O → 2NaOH (or)

2. If magnesium is burned in air it forms magnesium oxide.
Mg → Mg²⁺ + 2e-
O + 2e^– → O^2-
Mg²⁺ + O^2- → MgO

3. Copper and iron combine with oxygen at high temperature in dry air.

II. Reaction of metals with dilute acids. Metals reacts with dilute acids to produce hydrogen gas. Rate of reactivity is different.
1. Na, K, Zn, Mg, Fe etc. are reactive in decreasing order.
2Na + HCl → 2NaCl + H₂ ↑
Mg + 2HCl → MgCl₂ + H₂↑
Zn + H2SO₄ → ZnSO₄ + H₂↑

2. Dilute nitric acid reacts with metals like Cu, Ag, Pb, Hg to form NO (nitrogen oxide).
Cu + 8HNO₃ → 3Cu (NO₃)₂ + 2NO + 4H₂O
3Ag + 4HNO₃ → 3AgNO₃ + NO + 2H₂O

3. Dilute nitric acid reacts with Mg and Mn to produce hydrogen gas.
Mg + 2HNO₃ → Mg (NO₃)₂ + H₂ ↑

4. Gold and platinum do not react with dilute acids.

III. Reaction of metals with chlorine. Metals combines with chlorine to form electrovalent chlorides.
Ca + Cl₂ → CaCl₂

IV. Reaction of metals with hydrogen. Reactive metals like Na, K, Ca etc. react with hydrogen to form hydrid.
2Na + H₂ → 2NaH
Ca + H₂ → CaH₂

V. Reaction of metals with water:
1. Water at normal temperature react with Na, K and Ca to liberate hydrogen gas.
2Na + 2H₂O → 2NaOH + H₂ ↑
Ca + 2H₂O → Ca (OH)₂ + H₂ ↑

2. Mg, Zn and Fe react with boiling water to form oxide.
Mg + H₂O → MgO + H₂ ↑
3Fe + 4H₂O → Fe₃O₄ + 4H₂ ↑

Question 12.
What is roasting? When do you use it?
Answer:
Roasting. After enrichment of ore, it is heated in the presence of dir, this process is called roasting sulphides or carbonates of some metals are converted into oxides, because extraction of metal is easy from oxides. Carbonates and sulphides of zinc and lead are converted into oxides by roasting.

Question 13.
If a copper plate remains immersed in silver nitrate solution for some time then what happens? Write the ionic equation for the reaction.
Answer:
Copper is more reactive than silver. Copper will displace silver from the solution and silver gets deposited on copper. Colour of the solution becomes blue.

Question 14.
Copper sulphate solution is stored in an iron container. After some days holes were seen in the container. Write the reaction. Explain the reaction on the basis of activity series.
Answer:
Iron is more reactive than copper and is placed before copper in the activity series. Therefore iron can displace copper from copper sulphate solution, due to this reaction holes were seen in the container.
CuSO₄ + Fe → FeSO₄ + Cu
Cu²⁺ (aq) + Fe(s) → Fe²⁺ (aq) + Cu(s)
Thus iron displaced copper.

Question 15.
Why copper becomes green if left open in air. Why?
Answer:
Copper reacts with moist carbon dioxide which is present in air. This makes its surface dull and a green layer is seen on the surface of copper. This green substance is copper carbonate.

Question 16.
What is 24 carat gold?
Answer:
Pure gold is called 24 carat gold. It is very soft. It can be used to make ornaments. Small amount of silver or copper is mixed with it to make it harder. In our country usually 22 carat gold is used to make ornaments. This means 22 pure gold is mixed with 2 parts of copper or silver.

Question 17.
Which process is used for the enrichment of sulphide ore. Explain in brief two steps involved in the extraction of metal from enriched sulphide ore.
Answer:
Sulphide ore is finely grounded to get powder. This is then enriched by using ‘Froth floation process’.

Steps involved in the extraction of metal from enriched sulphide ore :
1. Roasting: Enriched ore is heated in the presence of air to get oxides. This process is called roasting.

2. Reduction. Oxide of the enriched ore is heated with reducing agent to extract the metal.

Question 18.
Give differences :
(i) Hydraulic washing and liquation.
Answer:

Hydraulic Washing	Liquation
1. This process is used for concentration of an ore.	1. The process is used for refining of metals.
2. Ore is washed with washing.	2. This is used for refining metal having low melting points.

(ii) Electrolytic reduction and reduction by carbon.
Answer:

Electrolytic reduction	Reduction by carbon
1. Here cathode acts as reducing agent. It converts metal ions into metals by providing electrons.	Carbon is used as reducing agent.
2. This method is used to reduce the salts of highly reactive metals.	2. This method is used to reduce the oxides of metals which are in the middle of activity series.

Question 19.
An alloy of yellow’ colour is made up of two metals A and B. When this alloy was dipped in dilute sulphuric acid, a layer dissolved in acid and formed colourless solution. B did not dissolve in it and the surface of alloy attained red brown colour. What is A and B?
Answer:
Yellow coloured alloy is brass which is mixture of zinc and copper. In this A is zinc and B is copper.
Zn + H₂SO₄ → ZnSO₄ + H₂

Question 20.
Sulphur dioxide (SO₂) gas is produced when a certain ore is heated. Write the method involved in the extraction of metal from this ore.
Answer:
SO₂ gas is produced when copper pyrites an ore of copper is heated.

Following steps are involved in the extraction of metal from this ore :
1. Ore is ground to get powder. It is mixed with water and pine oil. Compressed air is blown to separate impurities. This way ore gets enriched, this method is called froth floatation method.

2. Now the enriched ore is roasted. A part of CuS converts to CuO

Copper is in liquid state and is purified by electric refining.

3. Electrical refining. In this process impure copper rod is taken as anode and pure copper plate is taken as cathode. Electric current is passed through copper sulphate solution in the presence of acid

Question 21.
What is Thermite process? Write its uses.
Answer:
Some displacement reactions are highly exothermic. The quantity of heat produced is so high that metals obtained are in molten state. When Iron (III) oxide (Fe₂O₃) reacts with aluminium then a large amount of heat is produced.
Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + heat

This is known as thermite process. This process is used to weld the rails and to join the cracks in machines.

Question 22.
Give five uses of non-metals.
Answer:

• Hydrogen is used in the preparation of vegetable oil.
• Carbon is an important non-metal which is main constituent of vitamins, proteins, carbohydrates, enzymes etc. Graphite is used as an electrode in various cells.
• Nitrogen is used in ammonia, Nitric acid and fertilizers. Its presence in air controls the rate of combustion.
• Presence of oxygen is the base of our life. Combustion is also possible in the presence of oxygen.
• Sulphur is used in many medicines and is also used to make explosives.

Question 23.
Differentiate Roasting and Calcination.
Answer:

Roasting	Calcination
1. Roasting is used for sulphide ores.	1. Calcination is used for carbonate and hydrated ores.
2. Ore is heated in the presence of air.	2. Ore is heated in the absence of air.
3. SO2 gas is produced.	3. CO2 gas is produced.

Question 24.
How is ionic compound sodium chloride, forms from sodium and chlorine?
Answer:
Sodium and chloride ions are oppositely charged and thus attract each other
They are bound together by strong electrostatic force of attraction and exist in the form of sodium chloride (NaCl). Sodium chloride does not exist as a molecule but as a set of ions :

Question 25.
Ionic compounds are insulators when in solid state whereas when in aqueous solution they become conductors. Why?
Answer:
There exist a strong force of attraction between positive and negative ions of the ionic compounds, due to which these compounds are solid and hard. Due to their firm and rigid structure ions cannot move. But in molten state or in aqueous solution the force between opposite ions become weak and the ions can move freely. Therefore electricity can pass through ionic compounds when in liquid form.

Question 26.
What is aqua regia? Explain.
Answer:
Aqua regia is a mixutre of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3 : 1. It can dissolve gold where no single acid can do this. Aqua regia (Latin word for Royal water) is highly corrosive and fuming liquid. It can also dissolve platinum.

Question 27.
Give two main ores of aluminium. Also give two alloys of aluminium.
Answer:
Two ores of aluminium are :

1. Bauxite, Al₂O₃. 2H₂O
2. Cryolite, Na₃ (AlF₆).

Two alloys of aluminium are :

1. Duralium
2. Magnalium.

Question 28.
Give uses of pure metals.
Answer:

• Copper and aluminium wires are used in the transmission of power (electricity).
• Utensils, Machines etc. are made up of iron, aluminium and copper.
• Gold and silver are used to make ornaments, these are also used in sweets in the form of silver foil.
• Metals like cadmium, titanium, zinconium etc. are used in nuclear energy and space science projects.
• Aluminium foil is used to wrap eatables.
• Titanium and its alloys are used in airplane, airplane structure and engine, chemical reactor.
• Metals are used in broken bones and body parts.

Question 29.
Which gas is produced, when reactive metals come in contact with dilute hydrochloric acid? Write the chemical reaction between iron and dil. H₂SO₄.
Answer:
When reactive metals come in contact with dil. hydrochloric acid then (H₂) hydrogen gas is produced.
Hydrogen gas is produced when iron reacts with dil. H₂SO₄.
Fe + H₂SO₄ → FeSO₄ + H₂ ↑

Question 30.
What is the function of cryolite in the electrolytic reduction of alumina?
Answer:
Cryolite has two functions in the extraction of aluminium :

• To reduce the melting point of alumina.
• Alumina is bad conductor of electricity on mixing cryolite (Na₂AlF₃), Al²⁺ ions are produced from alumina.

Question 31.
How do iron and aluminium react with water?
Answer:
Aluminium and iron do not react with cold or hot water. But react with steam to form metal oxide and hydrogen.
2Al(s) + 3H₂O(g) → Al₂O₃(s) + 3H₂(g)
3Fe(s) + 3H₂O(g) → Fe₃O₄(s) + 3H₂(g)

Question 32.
What happen when :
(i) Iron oxide is heated with coke?
Answer:
Iron oxide is readuced to iron.

(ii) Magnesium is treated with dilute sulphuric acid?
Answer:
Hydrogen is produced

(iii) Zinc is added to blue vitriol solution?
Answer:
Blue colour of solution gradually faders away

Question 33.
What is rust? Explain it with the help of a chemical reaction.
Answer:
If iron is left open in moist air, a brown layer is produced on its surface. This brown coloured layer is of Ferric oxide and ferric hydroxide. This is called rust. This makes iron weak.
4Fe + 3O₂ + 3H₂O → Fe₂O₃ + 2Fe(OH)₃

Question 34.
Write names of main alloys and their constituents?
Answer:

Alloys	Constituents	Uses
1. Steel	Iron, carbon	used in airplanes, buildings vehicles etc.
2. Stainless steel	Iron, Carbon, Chromium	utensils, machine parts, knife, blade, food and milk industry, nuts, bolts, taps etc.
3. Brass	Copper, Zinc	utensils, idols, airplanes, medals, steam driven train parts etc.
4. Bronze	Copper, tin	utensils and other apparatus.
5. Solder	Lead, tin	For joining/welding electric wires.
6. German Silver	Copper, Nickel, zinc	Airplane wings, utensils used in kitchen of airplanes and other mate­rials.
7. Bell metal	Copper,tin	For making bells.
8. Duralium	Aluminium, copper magnesium and mangnese in very small amount.	In airplane
9. Magnoleum	Aluminium, magnesium	Light weight tools and cheap utensils.
10. Gun metal	Copper, tin, zinc	For making gears of vehicles and machines.

Question 35.
Write the names of metals found in Bronze and Duralium, give uses of these alloys.
Answer:
Bronze. It is 90% copper and 10% tin. It is used in idols, medals, coins and vessels used for cooking food.
Duralium. It consists of 95% aluminium, 4% copper, 0.5% magnesium and 0.5% manganese. It is used in aeroplanes, space crafts, kitchen vessels.

Question 36.
What is rust? What is its chemical formula?
Answer:
When iron is left open in air, then a layer of iron oxide is formed on the surface of iron. This brown matter is rust. It corrodes the metal. Its chemical formula is Fe₂O₃. xH₂O.

Question 37.
What are metals?
Answer:
The elements which are on the left and in the middle of the periodic table and have metallic lustre are called metals. These are usually ductile, malleable, good conductor of electricity and heat, hard and have high density. They form basic oxides. Examples of metals are gold, iron, silver, copper, platinum etc.

Question 38.
What is ihe reason of catching fire by potassium and sodium on their own?
Answer:
Potassium and sodium reacts with water vigorously and violently. The reaction is very violent and highly exothermic that hydrogen produced in the reaction catches fire on its own.

Question 39.
Observe the figure given below and name the gas produced. Also give the chemical equation.

Answer:
Hydrogen gas is produced

Question 40.
What is indicated by the following figure?
Or
With the help of a labelled diagram prove that both oxygen/air and water are necessary for rusting of iron.

Answer:
Both air and moisture are required for rusting of iron.

Question 41.
Why the substance obtained by mixing small amount of carbon in iron is used largely for various purposes?
Answer:
When small amount of carbon is mixed with iron it changes to steel. This is stronger than iron. It can be used in ships, vehicles, dams.

Question 42.
Write a chemical equation for the reaction taking place in the test tube. How does the colour of solution change? What is change in colour of iron nails?

Answer:

The colour of the solution changes from blue to light green. The colour of Iron nails changes from grey to brown.

Very Short Answer Type Questions

Question 1.
Give one example of metal which is liquid at room temperature.
Answer:
Mercury.

Question 2.
Name one metal and one non-metal which is liquid at room temperature.
Answer:
Metal-Mercury.
Non-Metal—Bromine

Question 3.
Name one non-metal which has bright lustre.
Answer:
Iodine.

Question 4.
Name one non-metal which does not have bright.
Answer:
Phosphorus.

Question 5.
Which of the following metal are liquid at body temperature (37° C): Gallium, Magnesium, Caesium, Aluminium.
Answer:
Gallium and Caesium.

Question 6.
Name one non-metal which is a good conductor of electricity?
Answer:
Graphite (Carbon).

Question 7.
Arrange the following metals in the decreasing order of reactivity,
Fe, Zn, Cu, Na, Ag.
Answer:
Na > Zn > Fe > Cu > Ag.

Question 8.
Out of Sodium, Calcium, Aluminium, Copper and Magnesium name the metal which reacts with
(i) Boiling water
Answer:
Magnesium

(ii) Steam.
Answer:
Copper.

Question 9.
Sodium metal is kept under kerosene oil, why?
Answer:
This is because sodium reacts with moist air as well as water.

Question 10.
A non-metal X, exists in two forms Y and Z. Y is the hardest substance and Z is a poor conductor of electricity. What are X, Y and Z?
Answer:
Y = Diamond Z = Graphite X = Carbon
Y and Z are allotropic forms of carbon.

Question 11.
An element, A form two oxides AO and AOa. AO is neutral and AO₂ is acidic : Indicate whether A is metal or non-metal.
Answer:
A is non-metal.

Question 12.
Name the reaction to convert metal into its oxide .
Answer:
Oxidation.

Question 13.
Ionic solids have high melting points, why?
Answer:
In ionic solids, there are strong electrostatic forces of attraction between the oppositely charged ions and a large amount of energy required to overcome these forces.

Question 14.
An element X reacts with oxide to form oxide, X₂O which dissolves in water and turns red litmus solution blue. Give the nature of oxide and indicate X is metal or non-metal.
Answer:
X₂O is basic. X is metal.

Question 15.
What is the nature of metal oxides?
Answer:
Basic.

Question 16.
Name two noble metals.
Answer:
Gold and platinum.

Question 17.
Name an ore of mercury.
Answer:
Mercury sulphide (Hgs).

Question 18.
Name two metalloids.
Answer:
Arsenic, antimony.

Question 19.
Metals lose lustre when placed in air, why?
Answer:
This is because their surfaces are covered with oxides, carbonates or sulphide layer’s .

Question 20.
Name two metals which can be cut with a knife.
Answer:
Sodium and potassium.

Question 21.
Why do metals aquire different shapes?
Answer:
This is due to malleability and ductility of metals.

Question 22.
Name the metal which is poor conductor of heat.
Answer:
Lead.

Question 23.
Name the metal which offers resistance to the flow of electricity.
Answer:
Mercury.

Question 24.
Which of the following metals can be drawn into wires?
Answer:
Cu, Al, Fe, Pb.

Question 25.
Name four non-metals which are solid at room temperature.
Answer:
Carbon, Sulphur, Phosphorous, and iodine.

Question 26.
Name the elements which are present in abundance in earth’s crust.
Answer:
Oxygen and silicon.

Question 27.
What are alkalies? Give one example.
Answer:
Alkali. It is a metal hydroxide soluble in water Example : Sodium hydroxide (NaOH).

Question 28.
Name two amphoteric oxide.
Answer:

1. Aluminium oxide (Al₂O₃)
2. Zinc Oxide (ZnO)

Question 29.
What happens when magnesium is heated to ignition temperature?
Answer:
Magnesium burns with white light producing magnesium oxide.

Question 30.
Name the metal which does not react with dil. HCl.
Answer:
Copper.

Question 31.
Name two metals which react with hydrogen.
Answer:
Sodium and potasium.

Question 32.
Give the reaction when a piece of Calcium reacts with water.
Answer:
Ca + 2H₂O → Ca (OH)₂ + 4H₂.

Question 33.
Give the reactions when red hot iron reacts with steam.
Answer:
Ca + 4H₂O → Fe₃O₄ + H₂.

Question 34.
Why is zinc oxide called amphoteric oxide?
Answer:
This is because zinc oxide reacts with both acid as well as base.

Question 35.
The metals Na, K and Ca react with hydrogen to form hydroxide but other metals don’t, why?
Answer:
This is because Na, K and Ca are highly reactive metals.

Question 36.
Give the reactions which occur when zinc plate is added to copper sulphate solution.
Answer:
Zn + CuSO₄ → ZnSO₄ + Cu.

Question 37.
Out of the metals, Na, Cu, Au, which is
(i) Most reactive and
Answer:
Most reactive metal-Sodium (Na)

(ii) Least reactive?
Answer:
Least reactive metal-Gold (Au).

Question 38.
Arrange the following metals in the decreasing order of reactivity, Zinc, Mercury and Aluminium.
Answer:
Al < Zn < Hg.

Question 39.
Name two metals which occur in free state in nature.
Answer:
Gold and Platinum.

Question 40.
Define corrosion of metals.
Answer:
It is the interaction of surface of metal with air and moisture forming a layer of oxide, halide or carbonate layer on its surface.

Question 41.
Name a metal which undergoes corrosion in air.
Answer:
Iron.

Question 42.
Name two metals which are not corroded easily.
Answer:
Gold and silver.

Question 43.
Why does copper utensils turn green on exposure to air?
Answer:
Copper reacts with oxygen, carbon dioxide and moisture to form a green coloured compound (basic copper carlxmate):

Question 44.
Name two metals which are both malleable and ductile.
Answer:

1. Copper
2. Aluminium.

Question 45.
Name the most abundant metal in the earth’s crust.
Answer:
Aluminium.

Question 46.
Name the metal that gives a green coating when exposed to moisture.
Answer:
Copper.

Question 47.
Which is the most lightest metal known to us?
Answer:
Lithium.

Question 48.
Name two metals which occur in free state in nature.
Answer:

1. Gold
2. Platinum.

Question 49.
Name one of the most common ore of aluminium.
Answer:
Bauxite (Al₂O₃. 2H₂O).

Question 50.
What is an amalgam?
Answer:
An amalgam is an alloy of mercury with some other metals.

Question 51.
Name two metals which :
(a) readily burn in air an
Answer:
Metals which readily burn in air are :

1. sodium
2. magnesium.

(b) do not burn.
Answer:
metals which do not burn readily in air are :

1. Copper
2. iron.

Question 52.
Name the metal which is best conductor of electricity.
Answer:
Silver.

Question 53.
Name one metal which reacts with cold water.
Answer:
Sodium.

Question 54.
Name one metal
(i) more reactive than hydrogen and
Answer:
Sodium

(ii) less reactive than hydrogen.
Answer:
Silver.

Question 55.
Write the chemical name of any one compound ore of sulphur.
Answer:
Zinc sulphide (ZnS).

Question 56.
Name the metal used in galvanisation of iron.
Answer:
Zinc.

Question 57.
The metal which is found in nature in the free state is
Answer:
Gold and Platinum.

Question 58.
What chemical process is used for obtaining a metal from its oxide?
Answer:
Reduction process.

Question 59.
Which metals do not corrode easily?
Answer:
The metals which are not attacked by air and moisture don’t corrode easily.

Multiple Choice Questions :

Question 1.
The non-metal which is liquid at room temperature is:
(A) Chlorine
(B) Bromine
(C) Fluorine
(D) Iodine.
Answer:
(B) Bromine

Question 2.
Most reactive metal is:
(A) Na
(B) Mg
(C) Au
(D) K
Answer:
(D) K

Question 3.
The property due to which metals can be beaten into sheets is :
(A) Malleability
(B) Ductility
(C) Metallic lustre
(D) Hardness.
Answer:
(A) Malleability

Question 4.
The axnphoteric oxide is:
(A) ZnO
(B) BaO
(C) K2O
(D) Na2O.
Answer:
(A) ZnO

Question 5.
Copper gets covered with green layer when exposed to air due to the formation of:
(A) CuSO₄
(B) CuCO₃. Cu(OH)₂
(C) Cu (NO₃)₂
(D) CuO.
Answer:
(B) CuCO₃. Cu(OH)₂

Question 6.
During galvanisation, the metal whose layer is deposited is:
(A) Gallium
(B) Aluminium
(C) Zinc
(D) Silver.
Answer:
(C) Zinc

Fill in the blanks:

Question 1.
Brass is an alloy of copper and ____________
Answer:
Zinc.

Question 2.
____________ is the best conductor of electricity.
Answer:
Silver.

Question 3.
All the ores are ____________
Answer:
Minerals.

Question 4.
Copper can be refined by ____________
Answer:
Electrorefining.

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 3 Metals and Non-metals Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 3 Metals and Non-metals

PSEB 10th Class Science Guide Acids, Bases and Salts Textbook Questions and Answers

Question 1.
Which of the following pairs will give displacement reactions :
(а) NaCl solution and copper metal
(b) MgCl₂ solution and aluminium metal
(c) FeSO₄ solution and silver metal
(d) AgNO₃ solution and copper metal?
Answer:
(d) AgNO₃ solution and copper metal?

Question 2.
Which of the following methods is suitable for preventing an iron frying pan from rusting :
(a) applying grease
(b) applying paint
(c) applying a coating of zinc
(d) all of the above :
Answer:
(c) applying a coating of zinc

Question 3.
An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be :
(a) calcium
(b) carbon
(c) silicon
(d) iron.
Answer:
(a) calcium

Question 4.
Food cans are coated with tin and not with zinc because :
(а) zinc is costlier than tin
(b) zinc has a higher melting point than tin
(c) zinc is more reactive than tin
(d) zinc is less reactive than tin.
Answer:
(c) zinc is more reactive than tin

Question 5.
You are given a hammer, a battery, a bulb, wires and a switch.
(i) How could you use them to distinguish between samples of metals and non-metals?
(ii) Assess the usefulness of these tests in distinguishing between metals and non-metals.
Answer:
(i) Set up the electric circuit as shown below :

To distinguish between metals and non-metals on the basis of their electrical conductivity.

Insert the sample to be tested between clips A and B
If the bulbs glows, the sample is metal.
If the bulb does not glow, the sample is non-metal.
Thus metals are good conductors of electricity whereas non-metals are poor conductors of electricity.

(ii) If a substance produces a sound when struck beating with a hammer, it is a metal and if no sound is produced, it is a non-metal.
Metals are sonorous whereas non-metals are non-sonorous.

Question 6.
What are amphoteric oxides? Give two examples of amphoteric oxides.
Answer:
Amphoteric oxides. The metal oxide which react both with acids as well as bases to produce salts and water are known as amphoteric oxides.

Examples. Zinc oxide, ZnO Aluminium oxide, Al2O3

Question 7.
Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
Answer:
Zinc and magnesium can displace hydrogen from dilute acids. Copper and silver cannot displace hydrogen from dilute acids.

Question 8.
In the electrolytic refining a metal M, what would you take as the anode, the cathode and the electrolyte?
Answer:
During the electrorefining of metal, the impure metal is made as anode, a thin strip of pure metal M is made as cathode. The electrolyte used a soluble salt of metal M. to be refined.

Question 9.
Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it as shown in figure

Collection of Gas
(a) What will be the action of gas on
(i) dry litmus paper?
Answer:
No action.

(ii) moist litmus paper?
Answer:
It turns moist litmus paper red and then bleaches it.

(b) Write a balanced chemical equation for the reaction taking place.
Answer:
S + O₂ → SO₂

Question 10.
State two ways to prevent the rusting of iron.
Answer:
The rusting can be prevented by

1. By painting, oiling, greasing, galvanising, chrome plate or anodising.
2. By forming alloys.

Question 11.
What type of oxides are formed when non-metals combine with oxygen?
Answer:
As they form two types of oxides :
(a) Neutral oxides such as CO, NO etc.
(b) Acidic oxides such as SO₂, CO₂ etc.

Question 12.
Give reasons :
(a) Platinum, gold and silver are used to make jewellery.
Answer:
Platinum, gold and silver are used to make jewellery because these are not attacked by air and moisture. They don’t undergo corrosion and retain their lustre for a long time. Also these metals are malleable and ductile.

(b) Sodium, potassium and lithium are stored under oil.
Answer:
Sodium, potassium and lithium are stored under oil because in contact with moist air containing carbon dioxide, these are covered with a carbonate layer.
e.g. 4Na + O₂ → 2Na₂O
Na₂O + H₂O → 2NaOH
2NaOH + CO₂ → Na₂CO₃ + H₂O

Also they react with water.
e.g. 2Na + 2H₂O → 2NaOH + H₂.
Hence, these metals are stored under oil.

(c) Aluminium is a highly reactive metal, yet it is used to make utensils for cooking.
Answer:
This is due to the reason that a thin sticking oxide layer of aluminium is formed on its surface which prevents further reaction. Also aluminium is a good conductor of heat and the oxide layer (Al₂O₃) is stable even at high temperatures.

(d) Carbonate and sulphide ores are usually converted into oxides during the process of extraction.
Answer:
This is because it is easier to obtain a metal from its oxide as compared to its sulphide and carbonate ore.

Question 13.
You must have seen tarnished copper vessels being cleaned with lemon or tamarind juice. Explain why these sour substances are effective in cleaning the vessels.
Answer:
In tarnished copper vessel there is a layer of basic copper carbonate. This basic layer can be cleaned by using sour substances such as lemon or tamarind juice which are acidic in nature and dissolve the basic coat of copper carbonate

Question 14.
Differentiate betw een metals and non-metals.
Or
Differentiate between metals and non-metals on the basis of their chemical properties.
Answer:
Differences between metals and non-metals :

Metals	Non-Metals
1. They form basic oxides.	1. They form acidic or neutral oxides.
2. They displace hydrogen from dilute acids.	2. They don’t displace hydrogen from dilute acids.
3. Usually they don’t combine with hydrogen. Only a few reactive metals combine with hydrogen to form metal hydroxide which are electrovalent compounds.	3. They react with hydrogen to form hydrides which are covalent compounds.
4. They form chlorides which are electrovalent compounds.	4. They react with chlorine to form chlorides which are covalent compounds.

Question 15.
A man went door to door posing as a goldsmith. He promised to bring back the glitter of old and dull gold ornaments. An unsuspecting lady gave a set of gold bangles to him which he dipped in a particular solution. The bangles sparkled like new but their weight was reduced drastically. The lady was upset but after a futile argument the man beat a hasty retreat. Can you play the detective to find out the nature of the solution he had used?
Answer:
The solution used by goldsmith to bring back the glitter of old and dull gold ornaments was aqua regia. It is a freshly prepared mixture of cone. HCl and cone. HNOg in the ratio 3 : 1. It can dissolve gold,

Question 16.
Give the reasons why copper is used to make hot water tanks but steel (an alloy of iron) is not.
Answer:
This is because iron present in steel reacts with steam to form ferrosoferric oxide whereas copper has no action with water. As a result of it, the body of the steel tank becomes weaker and weaker in case of iron and not in case of copper.

Science Guide for Class 10 PSEB Metals and Non-metals InText Questions and Answers

Question 1.
Give an example of a metal which :
(i) is a liquid at room temperature
Answer:
Mercury

(ii) can be easily cut with a knife
Answer:
Sodium

(iii) it is the best conductor of heat
Answer:
Silver

(iv) is a poor conductor of heat.
Answer:
Lead.

Question 2.
Explain the meaning of malleable and ductile.
Answer:
Malleable: A substance is said to be malleable, if it can be beaten into sheets. e.g. metals are malleable.
Ductile: A substance is said to be ductile, if it can be drawn into wires e.g. the metals are ductile.

Question 3.
Why is sodium kept immersed in kerosene oil?
Answer:
This is because in contact with moist air containing carbon dioxide, it is covered with a carbonate layer.
4Na + O₂ → 2Na₂O
Na₂O + H₂O → 2NaOH
2NaOH + CO₂ → Na₂CO₃ + H₂O

Also sodium reacts with water.
2Na + 2H₂O → 2NaOH + H₂
Hence, sodium is kept immersed in kerosene oil.

Question 4.
Write equation for the reactions of
(i) iron with steam
Answer:

(ii) calcium and potassium with water.
Answer:
Ca + 2H₂O → Ca(OH)₂ + H₂
2K + 2H₂O → 2KOH + H₂

Question 5.
Samples of four metals A, B, C and D were taken and added to the following solution one by one. The results obtained have been tabulated as follows :

Use the table above to answer the following questions about metals, A, B, C and D.
(i) Which is the most reactive metal?
Answer:
B is the most reactive metal.

(ii) What would you observe if B is added to a solution of copper (II) sulphate?
Answer:
B will displace copper from copper sulphate solution.

(iii) Arrange the metals A, B, C and D in the order of decreasing reactivity.
Answer:
The decreasing order of reactivity is B > A > C > D.

Question 6.
Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H₂SO₄.
Answer:
Hydrogen gas is produced when dilute hydrochloric acid is added to a reactive metal.

Question 7.
What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place.
Answer:
When zinc is added to a solution of iron (II) sulphate it will displace iron from it and light green colour of solution gradually fades away.

Question 8.
(i) Write the electron-dot structures for sodium, oxygen and magnesium.
Answer:
Electron-dot structures for sodium, oxygen and magnesium are

(ii) Show the formation of Na₂O and MgO by the transfer of electrons.
Answer:
Formation of Na₂O:

(iii) What are the ions present in the above compounds?
Answer:

Question 9.
Why do ionic compounds have high melting points?
Answer:
In ionic compounds there are strong electrostatic forces of attraction between oppositely charged ion and a considerable amount of energy is required to break the strong interionic attraction.

Question 10.
Define the terms :
(a) mineral
Answer:
Mineral. The compounds of elements occurring in earth’s crust which are associated with earthly impurities are called minerals.

(b) ore
Answer:
Ore. An ore is a mineral from which metal can be extracted conveniently and economically.

(c) gangue.
Answer
Gangue. The earthly impurities such as sand, lime stone, rocks etc. associated with minerals and ores are collectively known as gangue or matrix.

Question 11.
Name two metals which are found in nature in the free state.
Answer:
Gold and Platinum.

Question 12.
What chemical process is used for obtaining a metal from its oxide?
Answer:
Reduction process.

Question 13.
Metallic oxides of zinc, magnesium and copper were heated with the following metals :

Metal	Zinc	Magnesium	Copper
Zinc oxide
Magnesium oxide
Copper oxide

In which cases will you find displacement reactions taking place?
Answer:
Zinc can displace copper from copper oxide

Magnesium can displace zinc from zinc oxide

Also Mg can displace copper from CuO

Question 14.
Which metals do not corrode easily?
Answer:
The metals which are not attacked by air and moisture don’t corrode easily.

Question 15.
What are alloys?
Answer:
Alloys. These are the homogeneous mixtures of two or more metals or metals and non-metals.