Important Questions

Punjab State Board PSEB 9th Class Science Important Questions Chapter 4 Structure of the Atom Important Questions and Answers.

PSEB 9th Class Science Important Questions Chapter 4 Structure of the Atom

Long Answer Type Questions:

Question 1.
What is Rutherford’s ∝-ray scattering experiment? Give its observations. How does Rutherford explain this observation?
Answer:
Rutherford’s ∝-ray scattering experiment: In this experiment, Rutherford obtained a thin stream of fast-moving alpha (∝) particles from radioactive source (P₀) and was allowed to strike against a thin foil of heavy metal like gold. Alpha particles are also called helium nuclei (He²⁺ with + 2 unit charge and 4 a.m.u. mass). As a result of the experiment, he made the following observations:

1. Most of the ∝-particles passed through the gold foil without any deflection from their original path.
2. Some of the ∝-particles got deflected by small angles from their original path.
3. A few ∝-particles (approximately 1 out of 10,000) were deflected to a large extent. In some cases, the a-particles came back in the same direction after striking the gold foil.

Explanation for the observations:

We know that the gold foil is made up of atoms of gold which are placed side by side. Since most of the ∝-particles passed through these atoms undeflected they did not come across any obstruction in their path, this shows that most of the space in the atom is light or hollow.

The electrons with negligible mass were supposed to be present in this portion called extra nuclear portion. The a-particies were deflected from their path and a very few came back in the same direction. This shows that they must have met with some obstruction in their path.
The obstruction must be
1. Heavy because a-particles are high speed particles and can remove light obstruction from their path.
2. Small because only a few a-particles got deflected.
3. Positively charged because some a-particles were repelled by this obstruction.

This small, heavy and positively charged portion inside an atom was called nucleus. The protons with mass and positive charge were supposed to be present in the nucleus. Later on, neutrons were also found to be present in the nucleus of the atom.

Question 2.
Discuss in brief Rutherford’s Model of atom.
Answer:
The main points of Rutherford’s model of atom are listed as follows:
1. An atom has two parts. These are nucleus and extra nuclear portion.
2. The nucleus contains protons while electrons are present in the extra nuclear portion.
3. Most of the mass of the atom is due to the nucleus because electrons have negligible mass.

4. The volume occupied by the nucleus is very small as compared to the volume occupied by extra nuclear portion.
5. The electrons in the extra nuclear portion are not stationary. These are revolving around the nucleus. The electrons are called planetary electrons because they can be compared to various planets which revolve around the sun. The nucleus may be compared with the sun.

Question 3.
Discuss the arrangement of the electrons in the different energy levels.
Or
Describe Bohr-Bury scheme for the distribution of electrons in the various orbits or energy levels of an atom.
Answer:
The distribution of electrons in the energy levels is given with the help of Bohr Bury scheme. It is given as follows:
1. The energy levels or energy shells are filled in order of increasing energies. The electrons first enter the K shell (n = 1. which is closest to the nucleus. This is followed by L shell (n = 2), M shell (n = 3) and so on. Here V represents the number of the shell.
2. The maximum number of electrons in any shell is given as 2n² (n = number of the shell). The distribution in the first four energy shells is given in the table given below:
Distribution of electrons in first four energy shells according to 2n² rule.

Symbol of shell	Number of shell (n)	Maximum number of electrons (2n2)
K	1	2 x (1)2 = 2
L	2	2 x (2)2 = 8
M	3	2 x (3)2 = 18
N	4	2 x (4)2 = 32

3. The outermost energy shell cannot have more than 8 electrons. The next inner shell called penultimate shell, cannot have more than 18 electrons.
4. It is not necessary that an energy level or shell is fully filled before the filling in the next energy level starts. In fact, filling of electrons in a new shell starts when any shell contains 8 electrons.
On the basis of the above scheme, let us discus with mass number 24 and atomic number 12.

• Mass no. of atom (A) = 24
• Atomic no. of atom (Z) = 12
• No. of protons in nucleus = 12
• No. of neutrons in nucleus = 12
• No. of electrons to be distributed = 12
• The distribution in the various energy shells: K L M: 2, 8, 2

Question 4.
Give the electronic distribution in the first twenty elements on the basis of Bohr-Bury scheme.
Answer:
On the basis of Bohr-Bury scheme, the distribution of electrons in first twenty elements (Z = 1 to Z = 20) is given below:
Table: Electronic distribution in atoms of first 20 elements

Element (Symbol)	Mass No. (A)	Atomic No. (Z)	No. of Protons (P)	No. of Electrons (e)	No. of Neutrons (n) (A-Z)	Electronic Distribution
						K	L	M	N
1. Hydrogen (H)	1	1	1	1	0	1
2. Helium (He)	4	2	2	2	2	2
3. Lithium (Li)	7	3	3	3	4	9	1
4. Beryllium (Be)	9	4	4	4	5	2	2
5. Boron (B)	11	5	5	5	6	2	3
6. Carbon (C)	12	6	6	6	6	2	4
7. Nitrogen (N)	14	7	7	7	7	2	5
8. Oxygen (O)	16	8	8	8	8	2	6
9. Fluorine (F)	19	9	9	9	10	2	7
10. Neon (Ne)	20	10	10	10	10	2	8
11. Sodium (Na)	23	11	11	11	12	2	8	1
12. Magnesium (Mg)	24	12	12	12	12	9	8	2
13. Aluminium (Al)	27	13	13	13	14 ‘	2	8	3
14. Silicon (Si)	28	14	14	14	14	2	8	4
15. Phosphorus (P)	31	15	15	15	16	2	8	5
16. Sulphur (S)	32	16	16	16	16	2	8	6
17. Chlorine (Cl)	35	17	17	17	18	2	8	7
18. Argon (Ar)	40	18	18	18	22	2	8	8
19. Potassium (K)	39	19	19	19	20	2	8	8	1
20. Calcium (Ca)	40	20	20	20	20	2	8	8	2

Special cases of Potassium and Calcium:

• In case of Potassium (Z = 19), the M shell has only 8 electrons and not 18. Actually, when the M shell gets 8 electrons, the filling of electrons starts in the next shell which is N-shell. When the N-shell gets 2 electrons, the electron are again- filled in the M shell.
• Thus, electronic distribution in potassium (Z = 19) is
  K L M N
  2 8 8 1 (M shell has 8 electrons and N shell has 1 electron)
• Similarly, the electronic distribution in calcium (Z = 20) is:
  K L M N: 2 8 8 2 (M shell has 8 electrons and N shell has 2 electrons)

Question 5.
Define the terms:

1. Atomic number
2. Mass number
3. Atom
4. Ion
5. Element
6. Orbit
7. Nucleons

Answer:

1. Atomic number: It is the number of protons present in the nucleus of an atom of the element.
2. Mass number: It is the sum of number of protons and neutrons present in the nucleus of an atom of the elements.
3. Atom: It is the smallest unit of matter which takes part in chemical reactions and it may or may not exist independently.
4. Ion: It is an atom or group of atoms having charge positive or negative and can exist freely in solution.
5. Element: It is a pure substance which can neither be built up nor broken into two or more still simpler substance by any physical or chemical method and it consists of only one kind of atoms.
6. Orbit: It is the fixed circular path traced by an electron revolving around the
7. Nucleons: The protons and neutrons present in the nucleus of an atom of the element are collectively known as nucleons.u

Short Answer Type Questions:

Question 1.
What do you understand by the structure of atom?
Answer:
According to the Dalton’s atomic theory, the smallest particle of matter is called atom. But later studies have shown that an atom is further made up of sub-atomic particles called electrons, protons and neutrons. Different atoms have different number of such particles and they also differ in the arrangement of these particles. Therefore, the atoms have different properties.

Question 2.
What happens when electric field is applied to the path of cathode rays? What does it show?
Answer:
When electric field is applied to the path of the cathode rays, these are deflected towards the positive plate of the field. This shows that the cathode rays consist of negatively charged particles.

Question 3.
What is the information conveyed by the following observations :

1. Atom is electrically neutral,
2. Mass of the atom is due to the nucleus.

Answer:

1. If an atom is electrically neutral, this means that it will have equal number of protons and electrons. Both protons and electrons have 1 unit charge but with opposite sign.
2. This means that nucleus contains in it both protons and neutrons which have mass.

Question 4.
What is the significance of number of protons found in the atoms in each of the different elements?
Answer:
The number of electrons in atom of the element is equal to the number of protons. By knowing no. of protons, we can calculate no. of electrons and hence its properties.

Question 5.
Write the electronic configuration of the elements A, B, C, D, E with atomic numbers 5, 6, 14, 13 and 15. Which have similar chemical properties?
Answer:

Element	Atomic No. (Z)	Electronic configuration
		K	L	M
A	5	2	3
B	6	2	4
C	14	2	8	4
D	13	?	8	3
E	15	2	8	5

Elements B and C. have similar chemical properties because both of them have 4 valence elt, trons.
Elements A and D have similar chemical properties because both of them have 3 valence electrons.

Question 6.
Five species P, Q, R, S, T have electrons, protons and neutrons are as follows:

Species	Electrons	Protons	Neutrons
P	4	3	4
Q	8	9	9
R	17	17	20
S	17	17	18
T	18	18	22

Find

1. a cation
2. an anion
3. a noble gas and
4. a pair of isotopes.

Answer:

1. Cation – Q
2. Anion – P
3. A noble gas = T
4. Pair of isotopes = R and S (because they have same number of electrons and protons but different number of neutrons).

Question 7.
Helium has only 2 electrons in the K-shell. But it is called an inert gas element. Why?
Answer:
Helium (He) atom has only one shell (K-shell) which can have a maximum of 2 electrons only. It cannot have more than 2 electrons. As a result, the combining capacity of He is zero. Therefore, its valency is also zero.

Question 8.
Give labelled diagram to show how are cathode rays produced?
Answer:

Question 9.
An atom has mass number A and atomic number Z.
1. How many protons are present in the nucleus?
2. How many electrons are revolving around the nucleus?
3. How many neutrons are present in its nucleus?
Answer:
Mass number = A
Atomic number = Z
1. No. of protons present in the nucleus = Z
2. No. of electrons revolving around the nucleus = Z
3. No. of neutrons present in the nucleus = A – Z.

Question 10.
State three ways by which a proton differs from an electron.
Answer:

Proton	Electron
1. It has one unit of positive charge. 2. It has mass 1.6 x 10-24 g. 3. It is present in the nucleus of an atom.	It has one unit of negative charge. It has mass 9.1 x 10″28 g. It is present in the extranuclear part of an atom.

Question 11.
What are isotopes? Give two uses of isotopes. Name the isotopes of hydrogen. Give their structures.
Answer:
Isotopes. The atoms of the same element having the same atomic number but different mass numbers are called isotopes.
Use of isotopes:
1. Isotopes of hydrogen, oxygen, carbon are used to study the mechanisms of organic reactions.
2. Some radioactive isotopes are used for the treatment of cancer and other diseases. The isotopes of hydrogen are:

Question 12.
Explain why elements have fractional atomic masses?
Answer:
The elements have fractional atomic masses due to the existence of isotopes (having different mass numbers) e.g. chlorine has two isotopes \({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) and are present in the ratio 3:1.
∴ Average atomic mass of chlorine = \(\frac{35 \times 3+37 \times 1}{4}=\frac{105+37}{4} \) = 35.5 a.m.u.

Question 13.
What are isobars? Give examples.
Answer:
The atom of different elements having same mass numbers but different atomic numbers are called isobars.
e.g. 1. \({ }_{18}^{40} \mathrm{Ar}\) and \({ }_{19}^{40} \mathrm{Ar}\)
2. \({ }_{36}^{86} \mathrm{Ar}\) and \({ }_{38}^{86} \mathrm{Ar}\)

Question 14.
Sulphur has an atomic number 16 and a mass of 32. State the number of protons and neutrons in the nucleus of sulphur. Give a simple diagram to show the arrangement of electrons in an atom of sulphur.
Answer:

Atomic number of S = 16
Mass number of S = 32
∴ No. of protons = 16
No. of neutrons = 32 – 16 = 16
No. of electrons = 16

Question 15.
Write down the electronic configuration of the following:
1. \({ }_{13}^{27} \mathrm{X}\)
2. \({ }_{17}^{35} \mathrm{X}\)
Write down the number of electrons in X and neutrons in Y and the formula of
compound formed by X and Y.
Answer:
1. \({ }_{13}^{27} \mathrm{X}\)
Atomic number of X = 13
Mass number of X =27
No. of protons in X = 13
∴ No. of electrons in X = 13
The electronic configuration of X = 2, 8, 3
Valency of X = 3

2. \({ }_{17}^{35} \mathrm{X}\)
Atomic number of Y = 17
Mass number of Y =35
No. of protons in Y = 17
No. of electrons in Y = 17
No. of neutrons in Y = 35 – 17 = 18
The electronic co0nfiguration of Y = 2, 8, 7
Valency of Y = 1
The formula of the compound formed by X and Y

Question 16.
Give the important properties or characteristics of isotopes.
Answer:

1. The isotopes of an element have same atomic number (Z) i.e. the same number of electrons and same number of protons. Hence, they have identical chemical properties.
2. Isotopes of an element have same number of valence electrons and hence same valency.
3. Isotopes of an element have different mass numbers (or different number of neutrons) and hence they have different physical properties such as mass, density, melting point, boiling point etc.

Question 17.
An atom of the element is represented as 11x?

1. What does the numeral 23 indicate?
2. What does the nemeral 11 indicate?
3. What is the number of protons in X?

Answer:

1. 23 indicates mass number of X.
2. 11 indicates atomic number of X.
3. No. of protons in X = Atomic number = 11.

Question 18.
The atom of an element is made up of 4 protons, 5 neutrons and 4 electrons. what are its atomic number and mass number?
Answer:
No. of proton = 4
Atomic number of the element, Z = 4
No. of neutrons = 5
∴ No. of protons + No. of neutrons =4 + 5 = 9
∴ Mass number of the element, A = 9.

Question 19.
Calculate the number of neutrons in the following elements:
1. \({ }_{1}^{3} \mathrm{Cl}\)
2. \({ }_{17}^{37} \mathrm{Cl}\)
3. \({ }_{20}^{40} \mathrm{Cl}\)
Answer:
1. \({ }_{1}^{3} \mathrm{Cl}\)
Mass number = 3
Atomic number = 1
No.of neutrons = Mass no – Atomic no.
= 3 – 1 = 2

2. \({ }_{17}^{37} \mathrm{Cl}\)
Mass number = 37
Atomic number = 17
No.of neutrons = 37 – 17 = 20

3. \({ }_{20}^{40} \mathrm{Cl}\)
Mass number = 40
Atomic number = 20
No.of neutrons = 40 – 20 = 20

Question 20.
Give two conditions under which cathode rays are produced.
Answer:
Cathode rays are produced when a gas is subjected to the action of
1. High voltage of the order of 5000-10000 V and
2. Under a low pressure of the order of 10^-3 atm of Hg.

Question 21.
The electronic configuration of P (Z = 15) is 2, 8, 5. Why is the valency of phosphorus 3 and not 5?
Answer:
The electronic configuration of phosphorus (P) shows that it has 5 valence electrons. Its valency is expected to be 5. But it is not possible for the atom to lose 5 electrons present in the valence shell because the energy required to remove these electrons will be very high. Therefore, phosphorus atom has valency equal to 3 because to gain 3 electrons is easier than losing 5 electrons as it requires less energy.

Question 22.
What information is conveyed by the statement that the mass number of magnesium is 24 and the atomic number is 12?
Answer:
The atomic number (12) of magnesium indicates that its atom has 12 protons in the nucleus and an equal number of electrons in the extra nuclear portion. The mass number (24) points out that there are also 12 neutrons (24 – 12 = 12) present in the nucleus alongwith protons.

Question 23.
Is it possible for an atom to have 12 protons and 13 electrons? Explain.
Answer:
No, it is not possible. An atom must always be electrically neutral. This means that it has no net charge present on it. Now, each proton has one unit positive charge and each electron has one unit negative charge. In a neutral atom, the number of electrons and protons must always be the same. Thus, an atom cannot have 12 protons and 13 electrons.

Question 24.
Give the important isotopes of hydrogen, carbon, oxygen and chlorine. Indicate their mass numbers and atomic numbers.
Answer:

Numerical Problems (Solved):

Question 1.
Chlorine has two isotopes \({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\) in the ratio 3 : 1. Calculate the average atomic mass of chlorine.
Solution:

Question 2.
Out of ₁₈X and ₁₆Y which atom is chemically more reactive?
Solution:

No. of valence electrons in X =8
No. of valence electrons in Y =6
∴ Y is more reactive.

Question 3.
An element has 12 neutrons and mass number 23. Give the atomic number and symbol of the element.
Solution:

• Mass number(A) = 23
• Number of neutrons = 12
• Number of protons = 23 – 12 = 11
• Atomic Number(Z)= 11
• Symbol of the element = \(\frac{23}{11} \mathrm{Na}\)

Question 4.
Calculate number of protons, neutrons and electrons in \(\frac{235}{92} \mathrm{U}\) and \(\frac{238}{92} \mathrm{U}\). How are these atoms related?
Solution:
table
\(\frac{235}{92} \mathrm{U}\) and \(\frac{238}{92} \mathrm{U}\) are isotopes.

Question 5.
Calculate the number of electrons, protons and neutrons is \(\frac{19}{9} \mathrm{U}\). Also calculate its valency.
Solution:

1. Atomic number = 9
2. Mass number = 19
3. No. of protons = 9
4. No. of neutrons = 19 – 9 = 10
5. Electronic configuration = 2 7
6. Valency = 8 – 7 = 1.

Very Short Answer Type Questions

Question 1.
Who discovered canal rays?
Answer:
Goldstein discovered canal rays in 1886.

Question 2.
Which charge is present on canal ray particles?
Answer:
They carry positive charge.

Question 3.
Which charge is present on protons?
Answer:
Positive charge.

Question 4.
Where are protons present in an atom?
Answer:
Protons are present in the nucleus, deep inside the atom.

Question 5.
What were the characteristics of an atom according to Dalton?
Answer:
According to Dalton an atom was indivisible and indestructible.

Question 6.
Which discovery is against Dalton’s theory?
Answer:
Discovering of electrons and protons in an atom.

Question 7.
Who proposed the first model for the structure of atom?
Answer:
J.J. Thomson.

Question 8.
Why did Rutherford used gold foil in a-ray scattering experiment?
Answer:
This is because he wanted as thin a layer as possible. It was about 1000 atoms thick.

Question 9.
What are α-particles?
Answer:
They are doubly charged helium ions (He²⁺).

Question 10.
What is the charge on α-particles?
Answer:
+2 units.

Question 11.
What is the mass of an α-particle?
Answer:
4 u.

Question 12.
How the defects of Rutherford’s model were removed by Neil Bohr?
Answer:
The electrons revolve around the nucleus in an atom in fixed circular paths called orbits or energy levels and don’t lose energy.

Question 13.
What are energy levels or shells?
Answer:
The definite orbits in where electrons revolve around the nucleus are called energy levels. These are designated as K, L, M, N ……………. 1, 2, 3, 4.

Question 14.
Define mass number of an element.
Answer:
It is the sum of number of neutrons and protons present in the nucleus of the atom of the element.

Question 15.
Who gave the distribution of electrons in the various shells of an atom?
Answer:
Bohr and Bury.

Question 16.
What is the maximum number of electrons present in an electronic shell?
Answer:
2n² (Where n is the number of shells).

Question 17.
What is the maximum first four shells of an atom?
Answer:
2, 8, 18, 32.

Question 18.
What is the maximum number of electrons in the outermost shell of an atom?
Answer:
8

Question 19.
Which elements are chemically inert?
Answer:
These are the elements which have 8 electrons in their outermost shells.

Question 20.
Define octet.
Answer:
The maximum number of electrons present in the outermost shell of an atom is called octet.

Question 21.
Define valency of an element.
Answer:
It is the combining capacity of an atom of the element and it is equal to the number of electrons lost or gained or contributed for sharing from its valence shell in order to complete its octet.

Question 22.
Define atomic number.
Answer:
It-is the number of protons present in the nucleus of an atom of the element.

Question 23.
Define nucleon.
Answer:
The neutrons and protons present in the nucleus of an atom of the element are collectively known as nucleons.

Question 24.
Where is most of the mass of the element present?
Answer:
In the nucleus of an atom.

Question 25.
Define atomic mass of an element.
Answer:
It is the sum of the number of neutrons and protons present in the nucleus of its atom.

Question 26.
What are isotopes?
Answer:
Atoms of the same element having same atomic number but different mass numbers are called isotopes.

Question 27.
Write two isotopes of chlorine.
Answer:
\({ }_{17}^{35} \mathrm{Cl}\) and \({ }_{17}^{37} \mathrm{Cl}\).

Question 28.
Write two isotopes of carbon.
Answer:
\({ }_{6}^{12} \mathrm{Cl}\) and \({ }_{6}^{14} \mathrm{Cl}\).

Question 29.
Isotope of which element is used in the treatment of cancer?
Answer:
Isotope of cobalt (\({ }_{27}^{59} \mathrm{Co}\)).

Question 30.
What is the atomic mass of chlorine?
Answer:
35.5

Question 31.
Isotope of which element is used for the treatment of goitre?
Answer:
An isotope of iodine.

Question 32.
Isotope of which element is used in atomic reactor?
Answer:
Uranium.

Question 33.
What are isobars?
Answer:
Atoms of the different elements having same mass number but different atomic numbers are called isobars.

Question 34.
Give one example of isobars?
Answer:
\(\underset{(\text { Calcium })}{\stackrel{40}{20} \mathrm{Ca}}\) and \(\underset{(\text { Argon })}{\stackrel{40}{18} \mathrm{Ca}}\).

Question 35.
Write three isotopes of hydrogen.
Answer:

1. Protium (\({ }_{1}^{1} \mathrm{H}\))
2. Deuterium (\({ }_{2}^{1} \mathrm{H}\))
3. Tritium (\({ }_{3}^{1} \mathrm{H}\)).

Question 36.
What is the total number of electrons in an atom if its K-and L-shells are fully filled?
Answer:
10 (K-2, L-8).

Question 37.
What electrons in an atom influence its chemical properties?
Answer:
Valence electrons (electrons in the outermost shell).

Question 38.
How will you represent chlorine atom having mass number 35 and atomic number 17?
Answer:
\({ }_{17}^{35} \mathrm{Cl}\)

Question 39.
Name the sub-atomic particle on which size of an atom depends?
Answer:
Electron.

Question 40.
Name the atoms having same atomic number but different mass numbers.
Answer:
Isotopes.

Question 41.
Mg²⁺ has 10 electrons, what is the number of protons in it?
Answer:
10 + 2 = 12.

Question 42.
Name the element which has no neutrons in the nucleus of its atom.
Answer:
Hydrogen.

Question 43.
Out of electrons, protons and neutrons, which are same in isotopes?
Answer:
Electrons and protons.

Question 44.
There are three isotopes of hydrogen, \({ }_{1}^{1} \mathrm{H},{ }_{1}^{2} \mathrm{H},{ }_{1}^{3} \mathrm{H}\) all are electrically neutral, why?
Answer:
This is because each isotope has one electron and one proton.

Question 45.
An element has atomic number 16. Give its electronic configuration and number of valence electrons.
Answer:
Electronic configuration 2, 8, 6.

Question 46.
The number of electrons in the valence shell of sodium (Na) is ……………… .
Answer:
1.

Question 47.
Fluorine belongs to …………… family.
Answer:
Halogen.

Question 48.
In an atom, the number of …………… is the same as the number of ………………. .
Answer:
Electrons, protons

Question 49.
Sodium has …………….. electron …………….. than sodium ion.
Answer:
One, more

Question 50.
Isotopes of an element are …………….. because they have ……….. number of electrons.
Answer:
Chemically similar, same

Question 51.
The number of electrons in the valence shell of an atom cannot be ………………..>
Answer:
More than eight.

Punjab State Board PSEB 9th Class Science Important Questions Chapter 3 Atoms and Molecules Important Questions and Answers.

PSEB 9th Class Science Important Questions Chapter 3 Atoms and Molecules

Long Answer Type Questions:

Question 1.
(a) Write the important postulates of the Dalton’s Atomic Theory.
(b) Give four drawbacks of Dalton’s Atomic Theory.
Answer:
(a) Dalton’s atomic theory was given by John Dalton in 1808 to e×plain the nature of an atom and the chemical combination in the atoms. The main points of the theory are:

1. All matter is made up of a large number of e×tremely small particles called atoms.
2. An atom cannot be further divided.
3. Atoms are of different kinds. There are as many kinds of atoms as are of elements.
4. Atoms of a particular element are identical in all respects i.e. they have same mass and similar properties.
5. Atoms of the different elements are different i.e. they have different masses and properties.
6. Two or more atoms of the same or different elements combine to form compound atoms or molecules of compounds.
7. The number and the nature of atoms in a molecule always remains the same.
8. Atoms of the different elements combine in a simple whole number but fi×ed ratios to form compound atoms (now called molecules).
9. Atoms of the same element can combine to form two or more compounds.
10. Atom can neither be created nor be destroyed.

(b) Drawbacks of Dalton’s Atomic Theory:

1. Atom is no longer indivisible.
2. Atoms of the same element may not be always identical.
3. Atoms of different elements may have same atomic masses.
4. It does not e×plain the cause of chemical combination.

Question 2.
How to write a chemical formula of an ionic compound from its radicals?
Answer:
While writing the formula of an ionic compound, the following steps are used :

1. Write down the symbol or formula of positive ion to the left and the symbol or formula of the negative ion to the right.
2. Shift the valency of positive ion to the lower right of the negative ion and the valency of negative ion to the lower right of the positive ion.
3. Take out the common factor if any.
4. The formula compound radical is enclosed in small brackets and subscript is put outside the bracket. The subscript 1 is omitted.

Example

Question 3.
How will you write the name of a binary molecular compound?
Answer:
A covalent compound made up of two elements is called a binary molecular compound, e.g. water (H₂0).
While writing the name of a binary molecular compound, first write the name of the element whose symbol appears on the left hand side in the molecular formula and write down the name of other element. The name of the other element should end with ‘ide’. The prefi×es di, tri, tetra, penta etc. are used to indicate 2, 3, 4, 5…. atoms of an element.

Some examples are:

• Compound – Name
• CO – Carbon mono×ide
• CO₂ – Carbon dio×ide
• ZnO – Zinc O×ide
• SO₂ – Sulphur dio×ide
• PCl₃ – Phosphorus trichloride
• PCl₅ – Phosphorus pentachloride

Question 4.
Give one experiment to prove the truth of law of conservation of mass.
Answer:
1. Prepare 5% solution of barium chloride and sodium sulphate in separate beaker.
2. Take a small amount of solution of barium chloride in a conical flask and a small amount of solution of sodium sulphate in an ignition tube.

3. Suspend the ignition tube carefully in the conical flask with a thread and cork it.
4. Weigh the flask carefully. To prove the law of conservation of mass
5. Tilt and swirl the flask such that the two solutions get mi×ed and react.
6. Cool the flask to room temperature and again weigh it. The weight remains unchanged showing the truth of the law.

Short Answer Type Questions

Question 1.
Differentiate between an atom and a molecule.
Answer:

Atom	Molecule
1. It is the smallest particle of an element which takes part in chemical reactions. It may or may not exist freely.	1. It is the smallest particle of a substance which can exist freely.
2. Generally it is highly reactive.	2. It is less reactive.
3. It is less stable.	3. It is more stable.
4. It can’t be sub-divided.	4. It can be sub-divided.

Question 2.
(a) What do you understand by the term chemical formula?
(b) What qualitative information is given by the formula NH₃?
Answer:
(a) Chemical formula. The symbolic representation of a molecule of a substance is called its chemical formula. It indicates the actual number of atoms of various elements present in one molecule of a substance.
(b) NH₃ represents ammonia.

Question 3.
Write down the formulae of:
(a) Aluminium oxide
(b) Aluminium chloride
(c) Hydrogen sulphide
Answer:

Question 4.
Calculate the relative molecular masses of:
(a) Water (H₂O)
(b) Nitric Acid (HNO₃).
Answer:
(a) Molecular mass of water (H₂O) = 2 × 1 + 16 = 2 +16 = 18u.
(b) Molecular mass of nitric acid (HNO₃) = 1 + 14 + 3 × 16 =1 + 14 + 48 = 63u.

Question 5.
Write down the names of the compounds represented by the following formulae:

1. Na₂CO₃
2. MgCl₂
3. Al₂ (SO₄)₂
4. K₂ S0₄
5. NiS0₄
6. KN0₃
7. CaC0₃

Answer:

1. Sodium Carbonate
2. Magnesium Chloride
3. Aluminium Sulphate
4. Potassium Sulphate
5. Nickel Sulphate
6. Potassium Nitrate
7. Calcium Carbonate.

Question 6.
Work out the formula of:
1. Ammonia
2. Carbon dio×ide
3. Carbon tetrachloride.
Answer:

Question 7.
Calculate the number of moles in:
1. 52 g of He
2. 12.044 × 10₂₃ atoms of He
Answer:

Question 8.
Give one e×ample in each case;
(a) Diatomic molecule
(b) Triatomic molecule
(c) Monoatomic molecule
Answer:
(a) Dihydrogen (H₂)
(b) Ozone (0₃)
(c) Helium (He).

Question 9.
An element A has a charge of 3+. Write down the formulae of its:
(a) Chloride
(b) Sulphate
(c) Nitrate and
(d) Phosphate
Answer:

Question 10.
Write the formulae and names of the compounds between:
1. Sodium and sulphate ions
2. Aluminium and chloride ions
Answer:

Question 11.
Write the formulae of the compounds formed by:

1. Cr³⁺ and F^–
2. Pb²⁺ and \(\mathrm{SO}_{4}^{2-}\)
3. Mg²⁺ and S^2-
4. \(\mathrm{NH}_{4}^{+}\) and \(\mathrm{Cr₂O}_{7}^{2-}\)
5. K⁺ and \(\mathrm{CrO}_{4}^{2-}\)

Answer:

Question 12.
Calculate the formula mass of Na₂CO₃.10H₂O.
Answer:
Formula mass of Na₂,CO₃.10H₂O = 2 × 23 + 12 + 3 × 16 + 10 (2 × 1 + 16)
= 46 + 12 + 48 + 10 (2 + 16)
= 46 + 12 + 48 + 180
= 286 a.m.u.

Question 13.
(a) What do you understand by trivial names of compounds?
(b) Give the chemical names of five such compounds and give their trivial names.
Answer:
(a) The names of the compounds which do not follow any systematic rules are called trivial names or common names.
(b)

Compound	Chemical name	Trivial name
NH3	Nitrogen trihydride (AZANE)	Ammonia
NaCl	Sodium chloride	Common salt or Table salt
H2O	Hydrogen hydroxide (OXIDANE)	Water
NaOH	Sodium hydroxide	Caustic soda
PH3	Phosphorous trihydride (PHOSPHANE) .	Phosphine.

Question 14.
Calculate:
1. The number of atoms in 46 g of Na
2. No. of molecules in 8 g of O₂
Answer:

Question 15.
An element × shows two valencies i.e. 2 and 4. Write the formulae of its o×ides.
Answer:

∴ Formula of oxide – xO

Question 16.
Write the formulae of the following salts:

• Zinc carbonate
• Ammonium sulphate
• Barium chloride
• Sodium nitrate
• Lead hydro×ide
• Potassium permanganate

Answer:

• Name of the compound – Formula
• Zinc carbonate – ZnCO₃
• Ammonium sulphate – (NH₄)₂SO₄
• Barium chloride – BaCl₂
• Sodium nitrate – NaN0₃
• Lead hydro×ide – Pb(OH)₂
• Potassium permangante – KMnO₄

Question 17.
Write the names of the following compounds:

1. Al₂(S0₄)₃
2. Mg(HCO₃)₂
3. (NH₄)₂S
4. KMnO₄
5. KClO₃

Answer:
Formula of the Compound Name

1. Al₂(S0₄)₃ – Aluminium sulphate
2. Mg(HC0₃)₂ – Magnesium bicarbonate
3. (NH₄)₂ S – Ammonium sulphide
4. KMnO₄ – Potassium permanganate
5. KClO₃ – Potassium chlorate

Numerical Problems (Solved)

Question 1.
Weight of copper o×ide obtained by treating 2.16 g metallic copper with nitric acid and subsequent ignition was 2.70 g. In another e×periment, 1.15 g of copper o×ide on reduction yielded 0.92 g of copper. Show that these results illustrate the law of definite proportions.
Solution:
First experiment

• Weight of copper = 2.16 g
• Weight of copper o×ide = 2.70 g
• Percentage of copper in copper o×ide = \(\frac{2.16}{2.70}\) × 100 = 80
• Percentage of o×ygen in copper o×ide = 100

Second Experiment

• Weight of copper o×ide = 1.15 g
• Weight of copper = 0.92 g
• Percentage of copper in copper o×ide = \(\frac{0.92}{1.15}\) × 100 = 80
• Percentage of O in CuO = 100 – 80 = 20
• Since the percentage composition of copper o×ide in the two e×periments is the same. The above results illustrate the law of definite proportions.

Question 2.
Carbon and oxygen combine in the ratio 3 : 8 by mass to form carbon dio×ide. What mass of o×ygen would be required to react completely with 6 g of carbon?
Solution:
3 g of carbon gas reacts with o×ygen = 8 g
∴ 6g of carbon gas will react with o×ygen = 8/3 × 6 = 16 g

Question 3.
In water molecule the ratio by mass in which hydrogen and o×ygen react is 1 : 8. Calculate the ratio by number of atoms in water molecules.
Solution:

Element	Ratio by mass	Atomic mass	Relative no. of atoms	Simplest Atomic ratio
H	1	1	1/1 = 1	2
O	8	16	8/16 = 1/2 = 0.5	1

∴ Ratio by atoms in water molecule is H : O
2 : 1

Question 4.
Calculate the formula masses of the compounds whose formulae are given below:

1. MgO
2. CaCl₂
3. CaC0₃

Solution:
Formula mass of

1. MgO – 24 + 16 – 40 amu
2. CaCl₂ = 40 + 2 × 35.5 = 40 + 71 = 111 amu
3. CaC0₃ = 40 + 12 + 3 × 16 – 100 amu

Question 5.
What is the weight of 01 mole of HCl?
Solution:
Molecular weight of HCl = 1 + 35.5 = 36.5
Therefore, according to the mole-concept,
Weight of 1 mole of HCl = 36.5 g
∴ Weight of 0.1 mole of HCl = 36.5 × 01 g = 3.65 g

Question 6.
How many g of H₂O are present in 0.2 mole of it?
Solution:
Molecular weight of H₂O = 2 × 1 + 16 = 18
Therefore according to the mole-concept,
Number of grams present in 1 mole of H₂O = 18
∴ Number of grams present in 0-2 mole of H₂O = 0.2 × 18 = 3.6.

Question 7.
What is the mass of 0.1 mole of CO₂ in g?
Solution:
Molecular weight of CO₂ = 12 + 2 × 16 = 44
Therefore according to the mole concept
Mass of 1 mole of CO₂ = 44 g
∴ Mass of 0.1 mole of CO₂ = 44 × 0.1 g = 4.4 g

Question 8.
Calculate the number of moles of phosphorus atoms (P) in 100 g of phosphorus (Atomic mass of P = 31).
Solution:
The gram atomic mass of phosphorus (P) = 31 g
31 g of phosphorus atoms = 1 mole
100 g of phosphorus atoms = 100/31 =3.2 moles.

Question 9.
How many grams of o×ygen gas contain the same number of molecules as are present in 16 grams of sulphur dioxide? (Atomic masses : S = 32, O = 16).
Solution:
Gram molecular mass of sulphur dio×ide (S0₂) = 32 + 2 × 16 = 64 g
64 g of S0₂ contains = 6.022 × 10₂₃molecules
∴ 16 g of S0₂ contains = \(\frac{6.022 × 10₂₃}{64}\) × 16 = 1.5 × 10₂₃ molecules
Gram molecular mass of o×ygen (O₂) = 32 g
Gram Molecular mass of O₂ contain = 6.022 × 10₂₃molecules
Now 6.022 × 10₂₃ molecules of O₂ = 32 g
∴ 1.5 × 10₂₃ molecules of O₂ = \(\frac{32 × 1.5 × 10₂₃}{6.022 × 10₂₃}\) = 7.97 g

Question 10.
What is the mass in grams of each of the following:
(a) 1.0 mole of Ag
(b) 0.5 mole of Mg
(c) 6.023 × 10₂₃ atoms of P?
(Atomic mass : Ag = 108, Mg = 24, P = 31).
Solution:
(a) Atomic mass of Ag = 108
Gram atomic mass of Ag = 108 g
Gram atomic mass of Ag is the mass of 1.0 mole of Ag atoms.
∴ Mass of 1.0 mole of Ag atoms in grams = 108 g

(b) Atomic mass of Mg = 24
Gram atomic mass of Mg = 24 g
Gram atomic mass of Mg is the mass of 1.0 mole of Mg atoms
∴ Mass of 1 mole of Mg atoms in grams = 24 g
Mass of 0.5 mole of Mg atoms in grams = 24 × 0.5 = 12 g

(c) Atomic mass of P = 31
Gram atomic mass of P = 31 g
Gram atomic mass of P contains 6.023 × 10₂₃ atoms of P
6.023 × 10₂₃ atoms of P weigh = 31 g.

Question 11.
Calculate the number of o×ygen atoms in 010 mole of Na₂CO₃ . 10H₂O.
Solution:
Number of oxygen atoms in one molecule of Na₂CO₃.10H₂O
= 3 + 10 = 13
∴ Number of oxygen atoms in 1 mole of Na₂CO₃.10H₂O
= 13 moles
= 12 × 6.022 × 10²³
= 78.286 × 10²³
= 7.8 × 10²⁴

Question 12.
Calculate the actual weight of:
(a) an atom of oxygen
(b) a molecule of NH₃.
Solution:
(a) Atomic weight of oxygen = 16
∴ 1 gram atom of oxygen = 16 g
According to the mole concept,
Number of atoms in 16 g of oxygen = 6.023 × 10²³
i.e. Actual weight of 6.022 × 10²³ atoms of oxygen = 16 g
∴ Actual weight of 1 atom of oxygen = \(\frac{16}{6.022 × 10²³}\) g
= 2.651 × 10²³ g

(b) Molecular weight of ammonia (NH₃) = 14 + 3 × 1 = 17
∴ 1 mole of ammonia = 17 g

Question 13.
Find the number of molecules in 1.8 g of H₂O.
Solution:
Molecular weight of H₂O = 2 × 1 + 16 = 18
∴ According to mole-concept,
Number of molecules in 18 g of H₂O = 6.022 × 10₂₃
= 6.022 × 10²³
∴ Number of molecules in 1.8 g of H₂O =
\(\frac{6.022 × 10²³}{18}\) × 18
= 6.022 × 10²²

Question 14.
Which of the following would weigh most?
(a) 1 Mole of H₂O
(b) 1 Mole of CO₂
(c) 1 Mole of NH₃
(d) 1 Mole of CO
Answer:
1 Mole of H₂O = (2 × 1 + 16) g = 18 g
1 Mole of CO₂ = (12 + 2 × 16) g = 44 g
1 Mole of NH₃ = (14 + 3 × 1) g = 17 g
1 Mole of CO = (12 + 16) g = 28 g
∴ 1 Mole of CO₂ weighs most.

Question 15.
Calculate the number of moles of phosphorus atoms in 100 g of phosphorus. If phosphorus is considered to contain P4 molecules, then how many moles it has?
Solution:
Atomic mass of phosphorus = 31
∴ According to mole-concept,
Number of moles of phosphorus in 31 g = 1
Number of moles of phosphorus in 100g = 1/31 × 100 = 3.22
If phosphorus is considered to contain P₄ molecules, then according to mole-concept, Number of moles in 4 × 31 i.e. 124 g = 1
∴ Number of moles in 100 g = 1/124 × 100 = 0.805

Question 16.
Find the number of hydrogen atoms in 0.1 mole of H₂SO₄.
Solution:
Number of hydrogen atoms in 1 mole of H₂SO₄ = 2 × 6.022 × 10₂₃
Number of hydrogen atoms in 0-1 mole of H₂SO₄ = 0.1 × 2 × 6.022 × 10₂₃
= 1.2044 × 10₂₃ = 1.2 × 10₂₃

Question 17.
Calculate the number of atoms in each of the following:
(a) 52 moles of He
(b) 52 amu of He
(c) 52 g of He
Solution:

Very Short Answer Type Questions:

Question 1.
When did Indian philosophers thought of division of matter?
Answer:
Around 500 B.C.

Question 2.
What was the view of Maharishi Kanad regarding the division of matter?
Answer:
The smallest particle of matter will be indivisible.

Question 3.
What was the name of smallest indivisible particle by Kanad?
Answer:
Atom.

Question 4.
Which two Greek philosophers considered smallest particle as indivisible?
Answer:
Democritus and Leucippus.

Question 5.
What is the ratio by mass of H and O in water?
Answer:
1 : 8.

Question 6.
What is the ratio by mass of N and H in NH3?
Answer:
14 : 3,

Question 7.
What is Prout’s law of constant composition?
Answer:
A pure chemical compound is always made up of same elements combined together in the same fixed ratio by mass.

Question 8.
Who gave Atomic theory?
Answer:
John Dalton.

Question 9.
When did John Dalton gave atomic theory?
Answer:
In 1808.

Question 10.
What are the units used to e×press the atomic radius?
Answer:
Nanometre (nm).

Question 11.
What is the relationship between m and nm?
Answer:
1 nm = 10-9m.

Question 12.
What is the building block of all matter?
Answer:
Atom.

Question 13.
Who was the first scientist which used symbols for elements?
Answer:
Dalton.

Question 14.
What was special about symbols of elements given by Berzelius?
Answer:
The symbols of elements were represented by one or two letters of the name of the element.

Question 15.
What were the units used for e×pressing atomic masses of elements initially?
Answer:
Initially 1 /16th of mass of an atom of naturally occuring oxygen (016-isotope) was taken as unit.

Question 16.
When was C¹² isotope universally accepted as standard reference for expressed atomic masses?
Answer:
In 1961.

Question 17.
Which unit is used now-a-days to e×press atomic masses?
Answer:
It is 1 /12th of mass of an atom of carbon (C¹² – isotope).

Question 18.
Name the smallest particle of an element or compound which can exist freely?
Answer:
Molecule.

Question 19.
What is obtained when the atoms of the same element combine?
Answer:
Molecule.

Question 20.
How many atoms are present in oxygen molecule.
Answer:
Two, hence, it is called diatomic molecule (O₂).

Question 21.
Give four examples of diatomic molecules.
Answer:
H₂, O₂, N₂ and Cl₂.

Question 22.
Give one example of tetra-atomic molecule.
Answer:
Phosphorous, (P₄).

Question 23.
Give one example sample of octa-atomic molecule.
Answer:
Sulphur, (S₈).

Question 24.
What is produced when three atoms of oxygen combine.
Answer:
Ozone (O₃).

Question 25.
Name isotopes of carbon.
Answer:
C¹², C¹³ and C^14.

Question 26.
What is the ratio by mass of C and O in carbon dioxide?
Answer:
3 : 8

Question 27.
What is the ratio by number between the atoms of H and O in water?
Answer:
2 : 1

Question 28.
Define an ion.
Answer:
It is an atom or group of atoms having charge (positive or negative).

Question 29.
What is a cation?
Answer:
It is an ion having positive charge.

Question 30.
What is an anion?
Answer:
It is an ion having negative charge.

Question 31.
What is the ratio by mass of Ca nd O in calcium oxide (CaO)?
Answer:
5 : 2

Question 32.
What is the ratio by mass of Mg and S in magnesium sulphate?
Answer:
3 : 4

Question 33.
What is the ratio by mass of Na and Cl in sodium chloride (NaCl)?
Answer:
23 : 35.5

Question 34.
Define chemical formula?
Answer:
It is the symbolic representation of a molecule of a substance.

Question 35.
Define valency.
Answer:
It is the combining capacity of an atom of the element.

Question 36.
What are diatomic molecules?
Answer:
These are made up of two atoms made up of same or different elements.

Question 37.
Define molecular mass of a subtance?
Answer:
It is the average relative mass of one molecule of substance as compared to the mass of one atom of carbon, (C¹²-isotope).

Question 38.
Which unit is used for expressing molecular masses?
Answer:
a.m.u.

Question 39.
What is the new name given to a.m.u. by IUPAC?
Answer:
U (Unified).

Question 40.
Name the elements present in water (H₂O).
Answer:
Hydrogen and oxygen.

Question 41.
What is one mole of an element?
Answer:
It is the number of an element whose mass in grams is numerically equal to its atomic mass e×pressed in a.m.u. or 1 gram atom of an element represents one mole.

Question 42.
What is Avogardro’s number?
Answer:
Avogardro’s number contains 6.022 × 10²³ particles.

Question 43.
How is Avogadro’s number denoted?
Answer:
By No or NA.

Question 44.
In what ratio elements combine to form a compound?
Answer:
In a fixed ratio by mass.

Question 45.
Which scientist gave law of conservation of mass?
Answer:
Russian scientist Lavoisier in 1756.

Question 46.
Which scientist gave law of constant composition?
Answer:
French scientist Joseph L. Proust in 1799.

Question 47.
What does a.m.u. represent?
Answer:
It is the unit used to express atomic masses.

Question 48.
Which isotope of carbon is used as a standard reference to express atomic masses?
Answer:
C¹² – isotope.

Question 49.
Most of the elements have fractional atomic masses, what does it show?
Answer:
This indicates the existence of isotopes of an element.

Question 50.
What is molar mass?
Answer:
It is the mass of 1 mole of a substance in grams.

Question 51.
Define gram atomic mass.
Answer:
It is the mass of 1 mole of atoms (6.022 × 10²³) in grams.

Question 52.
How many atoms are present in 1 gram atom of an element?
Answer:
6.022 × 10²³.

Question 53.
Do 1 mole of sodium and calcium have different number of atoms?
Answer:
No, they have same number of atoms.

Question 54.
Lead nitrate solution and sodium chloride solution taken in separate beakers. The beakers were weighed and mixed in one beaker and the beaker was weighed again. Does weight remains unchanged or not? On what principle, the answer is based upon?
Answer:
The weight remains unchanged. It is based upon law of conservation of mass.

Question 55.
28 g of magnesium oxide is produced by the combination of 12 g of magnesium and 16 g of oxygen. Which law is illustrated by this data?
Answer:
Law of conservation of mass.

Question 56.
Do 1 mole of Na and 02 have same mass?
Answer:
No, 1 mole of Na has mass = 23 g
1 mole of O₂ has mass = 32 g

Question 57.
1 mole represents particles …………. .
Answer:
6.022 × 10₂₃.

Question 58.
The molar mass of NH3 is
Answer:
17 g.

Question 59.
An element Z has a valency of 3. Write down the formula of its oxide?
Answer:
Z₂O₃.

Question 60.
How many atoms are present in 0.012 kg of C¹² – isotope? What is this number called?
Answer:
6.022 × 10²³ atoms. This number is called Avogadro’s number.

Question 61.
Write down the formula of compound made up of Al³⁺ and [latetx]\mathrm{SO}_{4}^{2-}[/latex].
Answer:
Al₂ (SO₄)₃

Question 62.
How many molecules are present in 9 g of water?
Answer:
9/18 × 6.0222 × 10₂₃ = 3.011 × 10₂₃ molecules.

Question 63.
What is the molecular mass of HN03. (Atomic masses, H = lu, N = 14u, 0 = 16u)
Answer:
1 + 14 + 3 × 16 = 1 + 14 + 48 = 63u.

Question 64.
What are polyatomic ions?
Answer:
It is a group of atoms having net charge, e.g. NH⁺₄, CO₃^2- etc.

Question 65.
The molecular formula of aluminium sulphate is ……….. .
Answer:
Al₂(SO₄)₃

Punjab State Board PSEB 9th Class Science Important Questions Chapter 2 Is Matter Around Us Pure Important Questions and Answers.

PSEB 9th Class Science Important Questions Chapter 2 Is Matter Around Us Pure

Long Answer Type Questions:

Question 1.
(a) Define mixture. Give examples.
(b) What are the types of mixtures?
Answer:
(a) Mixture. It is a product obtained by mixing two or more substances (elements and / or compounds) in any proportion. For example,

1. Air is a mixutre of nitrogen, oxygen, carbon dioxide, water vapour etc.
2. Smoke is a mixture of carbon particles and air.
3. Gun Powder is a mixture of nitre, sulphur and charcoal.
4. Brass is a mixture of copper and zinc.

(b) Types of mixtures. Mixtures are of two types:
1. Homogeneous mixtures and
2. Heterogeneous mixtures.
1. Homogeneous mixtures: A mixture in which the different constitutents are mixed uniformly and has the uniform composition throughout is called homogeneous mixture, e.g. Brass is a homogeneous mixture of copper and zinc, an aqueous solution of sodium chloride is a homogeneous mixture of sodium chloride and water.
2. Heterogeneous mixtures: A mixture in which the different constitutents are not mixed uniformly is called heterogeneous mixture, e.g. soil is a heterogeneous mixture, a mixture of common salt, sand and sulphur is a heterogeneous mixture.

Question 2.
Give important characteristics of a mixture.
Answer:
The important characteristics of a mixure are:

1. In a mixture, the components, elements or compounds are present in no fixed ratio.
2. A mixture is formed from its components as a result of physical change.
3. The properties of a mixture lie between those of its constituents.
4. A mixture may be homogeneous or heterogeneous.
5. The constituents of a mixture can be separated by physical methods only.
6. The formation of a mixture from its constituents does not involve any energy change.

Question 3.
What are the various types of binary solutions based upon the physical states
of solute and solvent?
Answer:
These are of nine types:

Solute	Solvent	Type of solution	Example
1. Solid	Solid	Solution of solid in solid	Brass
2. Solid	Liquid	Solution of solid in liquid	Sugar in water
3. Solid	Gas	Solution of solid in gas	Iodine in air
4. Liquid	Solid	Solution of liquid in solid	CuS04. 5H20
5. Liquid	Liquid	Solution of liquid in liquid	Ethyl alcohol in water
6. Liquid	Gas	Solution of liquid in gas	Moisture in air
7. Gas	Solid	Solution of gas in solid	Hydrogen in palladium
8. Gas	Liquid	Solution of gas in liquid	Carbon dioxide dissolved in water
9. Gas	Gas	Solution of gas in gas	Air

Question 4.
State briefly how would you separate or name the process use to separate:

1. Common salt from a solution of common salt and water.
2. Alcohol from a mixture of alcohol and water.
3. Sulphur from a mixture of carbon particles and powdered roll sulphur.
4. The coloured dyes in black ink.

Answer:

1. The solution containing common salt in water is concentrated and is then cooled. The crystals of common salt are formed which can be separated by filtration.
2. Alcohol can be separated from water by fractional distillation as the two liquids differ much in their boiling points.
3. The mixture is treated with carbon disulphide which dissolves powdered sulphur in it. It is filtered to separate carbon particles. The filtrate upon concentration and cooling gives crystals of sulphur which can be separated by the process of filtration.
4. The coloured dyes in black ink can be separated by the process of paper chromatography.

Question 5.
Give important differences between a compound and a mixture.
Answer:

Compound

Mixture

1. A compound is formed from its constituent elements as a result of chemical reaction. 2. A compound is always homoge­neous in nature. 3. In a compound the elements are present in a fixed ratio by weight. 4. The components of a compound can’t be separated by physical methods but can be separated by chemical methods only. 5. The properties of a compound are different from that of its elements. 6. The formation of a compound from its elements is accompanied by energy changes.

1. A mixture is obtained from its (elements, compounds) components as a result of physical change. 2. The mixtures can be homogeneous or heterogeneous. 3. In a mixture the components can be present in any ratio. 4. The components of a mixture can be separated by physical methods only. 5. The properties of a mixture lie between those of its components. 6. The formation of a mixture from its constituents is not accompanied by energy changes.

Question 6.
How are mixtures classified on the basis of their physical states?
Answer:
On the basis of their physical states, the mixtures are of the following types

Constituents of mixture	Nature of mixture	Example
1. Solid-Solid mixture	Homogeneous	Brass
2. Solid-Solid mixture	Heterogeneous	Common salt and sand
3. Solid-Liquid mixture	Homogeneous	Sugar in water
4. Solid-Liquid mixture	Heterogeneous	Sulphur in water
5. Liquid-Liquid mixture	Homogeneous	Water and alcohol
6. Liquid mixture	Heterogeneous	Carbon tetrachloride and water
7. Liquid-gas mixture	Homogeneous	Carbon dioxide dissolved in water
8. Gas-Gas mixture	Heterogeneous	A mixture of Nitrogen and Oxygen

Question 7.
Explain the following:
(a) Fractional crystallisation
(b) Sublimation
(c) Filtration
Answer:
(a) Fractional Crystallisation. The process of separation of components of a mixture having different solubilities in the same solvent is called fractional crystallisation. This method is used for the separation of components of a mixture which are soluble in the same solvent on heating but have different solubilities.
For example, a mixture of potassium nitrate and sodium chloride can be separated by this method.

This can be explained as follows:
The mixture is dissolved in water. The solid is concentrated to the crystallisation point. On cooling the crystals of less slouble component i.e., sodium chloride appear first. These are separated. On further cooling the crystals of more soluble component i.e., of potassium nitrate will appear. The pure crystals can be obtained by recrystallisation from the same solvent i.e, water.

(b) Sublimation: This method is used for the separation of the components of a mixture in which one component undergoes sublimation whereas other does not. For example, a mixture of ammonium chloride and common salt can be separated by this purpose take the mixture of ammonium chloride and common salt in a china dish. Cover it with an inverted funnel and its open end is to be closed with cotton wool. The walls of china dish are kept booled. On heating, ammonium chloride sublimes and condenses on the cooler parts whereas common salt is left behind. The fine powder of ammonium chloride deposited on the funnel is scrapped with the help of a knife.

Similarly, the mixture of iodine and sand can be separated by this method in which iodine sublimes whereas sand does not.

(c) Filtration. In this method, the mixutre is dissolved in a suitable solvent in which one component dissolves whereas other does not.

For example, a mixture of charcoal and sulphur can be separated by this method. The mixture is treated with carbon disulphide which dissloves sulphur whereas charcoal is left behind. The insoluble charcoal is separated by filtration and is dried. From the filtrate, sulphur can be obtained by evaporating carbon disulphide.

Question 8.
Explain the process of:
1. Distillation
2. Evaporation
Answer:
1. Distillation: The process of converting a liquid into gaseous state by heating to boiling point and condensing the vapour to get the pure liquid is called distillation.
For example, salt can be separated from sea water by this method. For this purpose the apparatus is fitted as shown below:

The mixture of solid and liquid is taken in a distillation flask. On heating vapour of liquid (water) are produced. These are condensed in water condenser and collected in a receiver. The non-volatile sodium chloride is left behind. Similar, a mixture of methyl alcohol and iodine i an be separated by this method.

2. Evaporation: Evaporation is a process of changing a liquid into its gaseous state by heating it at a temperature below its boiling point. For example, common salt can be obtained from a mixture of common salt and water by evaporation.

The mixture is heated in a china dish using sand bath when water vaporises whereas common salt is left behind.

Question 9.
What is chromatography? Why is it regarded as superior method of purification?
Answer:

• Chromatography. The process of separation of different components of a mixture by adsorbing them over a suitable material (called adsorbent) is called chromatography.
• Originally, this technique was used to separate coloured mixtures but now-a-days this method can be used for colourless as well as coloured substances.

The main advantages of this technique are:

1. It can be applied to separate the mixture even if very small amount of mixture of the substances is available.
2. The components of a mixture don’t get wasted during separation.
3. It also helps in estimating the constituents of a mixture apart from separation.

Question 10.
What is the principle of chromatographic separation? Name the different types of chromatography commonly used.
Answer:
Chromatography is based upon the distribution of the mixture of the components between the two phases i.e. a stationary phase and a moving phase. The moving phase consists of mixture of the substances to be separated. The moving phase is applied over a solid or liquid i.e., a stationary phase. The stationary phase separates the components of the mixture by the phenomenon of either partition, adsorption or ion exchange. The different chromatographic techniques are:
(a) Column chromatography
(b) Thin layer chromatography
(c) Ion exchange chromatography
(d) Paper chromatography.

Question 11.
How will you separate gas-gas mixtures?
Answer:
The gas-gas mixtures can be separated by the following method:
Fractional evaporation of mixture of liquefied gases. The mixture of two gases is liquefied by applying high pressure and then allowing it to expand. For example, when air is liquefied under high pressure and allowed to stand, both oxygen and nitrogen get liquefied.

The above liquid mixture is maintained at a temperature of -196°C (b.pt. of liquid N₂), nitrogen boils off. For example, a mixture of carbon dioxide and hydrogen can be separated by passing through porous partitions as showm below.

In this case, H₂ being lighter diffuses at a faster rate as compared to CO₂.

Question 12.
What are the various types of colloidal solutions based upon the physical states of dispersed phase and dispersion medium? Give one example in each case.
Answer:
These are of eight types:

Dispersed Phase	Dispersion Medium	Type or name of colloidal solution	Examples
1. Solid	Solid	Solid sol	Some coloured glasses
2. Liquid	Solid	Gel	Cheese, butter
3. Gas	Solid	Solid foam	Sponge, rubber foam
4. Solid	Liquid	Sol	Mud, milk of magnesia
5. Liquid	Liquid	Emulsion	Milk, hair cream
6. Gas	Liquid	Foam	Froth, whipped cream
7. Solid	Gas	Solid aerosol	Smoke
8. Liquid	Gas	Liquid aerosol	Fog, mist

Question 13.
Define concentration of a solution. How is concentration of a solution expressed?
Answer:
Concentration of a solution. It indicates the amount of solute dissolved per unit mass or volume of solvent or solution.
The concentration of a solution can be expressed as

Question 14.
Describe how you would separate the constituents of the following mixtures in a reasonably pure state:
(a) Sand and iodine
(b) Water and sugar
(c) Ingredients of gun powder
(d) Sulphur, sand and common salt
(e) Carbon dioxide and carbon monoxide.
Answer:
(a) Sand and iodine. The mixture can be separated by sublimation when iodine sublimes whereas sand is left behind.

(b) Water and sugar. Sugar and water can be separated by evaporation when water evaporates and sugar is left behind.

(c) Ingredients of gun powder. Gun powder is a mixture of sulphur, nitre and charcoal. Shake the mixture with water. Nitre passes into solution separated by filtration. Evaporate the filtrate. We get pure nitre.
Shake the residue obtained above with carbon disulphide when sulphur dissolves while charcoal is separated by filtration. From filtration sulphur is obtained by evaporating carbon disulphide.

(d) Sulphur, sand and common salt. Shake the mixture with water and filter. Common salt passes into solution. The filtrate is evaporated to get common salt.
Shake the residue obtained above with carbon disulphide and filter sulphur goes into the filtrate. Evaporate it when sulphur is left behind. Sand is left behind insoluble in carbon disulphide.

(e) Carbon dioxide and carbon monoxide. The mixture can be separated by diffusion through a porous pot when carbon monoxide differ faster than carbon dioxide and thus get separated.

Question 15.
What is paper chromatography? How will you separate the coloured constituents present in a mixture of ink and water?
Answer:
The process of separation of different dissolved components of a mixture by adsorbing them on a suitable material (called adsorbent) is called chromatography. The adsorbent can be solid or liquid. For example, alumina, magnesium oxide, special filter paper.
The components of a mixture are generally dissolved in a solvent like water, alcohol etc. If a filter paper is used as an adsorbent for the separation of components of a mixture, this technique is called paper chromatography.

The process of separation of coloured constituents present in a mixture of ink and water is described ahead:
1. Take a special filter paper about 25 cm long and 4 cm broad and stick it to a glass rod at its one end with the help of gum as shown below. Mark a line at a distance of 3 cm from the lower end with the help of pencil. Put a drop of ink at the centre of this line with the help of a fine capillary.
2. Dip this end in water taken in a beaker upto 2 cm.
3. Suspend this filter paper in a tall cylinder and allow it to stand undisturbed for one hour. The water rises up the filter paper and reaches the ink drop, dissolves its components and rise upwards along with water. The different components of ink are adsorbed upto different extents on the filter paper, therefore, they travel different distances on the filter paper.
4. After one hour, the filter paper is taken out and dried. Different of colours corresponding to the components of ink are produced on the filter paper. This filter paper is called chromatograph.

Question 16.
Briefly describe simple methods of separating the following mixtures:
(a) Powdered chalk and sugar
(b) Nitre and common salt
(c) Iron and copper filings
(d) Ammonium chloride, sand and common salt
(e) Ammonia and hydrogen.
Answer:
(a) Powdered chalk and sugar can be separated by using water which dissolves sugar and chalk is insoluble. It is separated by filtration. From sugar solution, sugar is obtained by evaporating water.

(b) Nitre and common salt. The mixture can be separated by fractional crystallisation from the solutions in water because they have different solubilities in water.

(c) Iron and copper filings can be separated by using a magnet when iron filings cling to magnet whereas copper filings don’t.

(d) Ammonium chloride, sand and common salt. Ammonium chloride is separated by sublimation. Sand and common salt are separated by using water when sand remains insoluble and is separated by filtration, From aqueous solution, sodium chloride can be separated by evaporation.

(e) Ammonia and hydrogen can be separated by diffusion through porous pot. Ammonia and hydrogen have different rates of diffusion due to different densities.

Question 17.
How will you separate liquid-liquid mixture or immiscible liquids?
Answer:
The liquid-liquid mixtures can be separated by using :
1. Separating funnel.
2. Fractional distillation.
1. Separation of liquid-liquid mixture by using separating funnel. This method is used when the two liquids are immiscible. For example, a mixture of carbon disulphide and wrater can be separated by this method.

The mixture is taken in a separating funnel. The funnel is allowed to stand for sometime. On standing, the liquid having higher density forms the lower layer whereas the liquid having lower density forms the upper layer. The two liquids are taken out from the separating funnel in separate conical flask.

2. Separation of liquid-liquid mixture using fractional distillation:

The process of separating the mixture of two immiscible liquids by using distillation carried out with the help of a long fractionating column is called fractional distillation.
For example, a mixture of ethyl alcohol and water can be separated by this method. The apparatus is fitted as shown below:

The mixture of ethyl alcohol anci water is heated in a distillation flask fitted with a fractionating column. On heating the vapour of liquid having lower boiling point are produced first and condensed in the water condenser and collected in a receiver. When the temperature of thermometer begins to rise, the vapour of other liquid are produced and these are condensed and collected in a separate receiver.

Question 18.
How will you separate the solid-liquid mixtures?
Answer:
The solid-liquid mixtures can be separated by the following methods:
1. By sedimentation and decantation. In this method, the mixture is allowed to stand when the solid particles settle down as sediment whereas clear liquid is left behind which is poured out carefully. This process is called decantation e.g. mixture of sand and water can be separated by this method. By this method, the complete separation is not possible.

2. By filtration. In this method, the mixture can be separated by using filter paper when the insoluble solid is left on the filter paper whereas the clear liquid passes out from the filter paper and is collected. For example, a mixture of chalk and water can be separated by this method.

Short Answer Type Questions:

Question 1.
Give three characteristics of a pure substance.
Answer:

1. It is homogeneous.
2. It has a definite set of properties.
3. A pure substance cannot be separated into other kinds of matter by any known physical method.

Question 2.
Give three examples each of two classes of pure substances.
Answer:
Pure substances are of two types:
(a) Elements e.g. carbon, nitrogen, oxygen etc.
(b) Compounds e.g. ammonium, water, carbon dioxide etc.

Question 3.
Give three characteristics of a mixture.
Answer:
(a) The components of a mixture are present in any ratio.
(b) It can be homogeneous or heterogeneous.
(c) The mixture can be separated with its constituents by physical or mechanical methods only.

Question 4.
Name the methods commonly used for separation of components of a mixture.
Answer:
These are:

1. Evaporation
2. Crytallisation
3. Centrifugation
4. Using separating funnel
5. Simple distillation
6. Fractional distillation
7. Chromatography
8. Sublimation

Question 5.
Define colloidal solution.
Answer:
It is a heterogeneous mixture or solution in which the particles having size 1 to 100 11m are suspended in a suitable solvent or dispersion medium. For example, starch solution.

Question 6.
Define dispersed phase and dispersion medium.
Answer:

• Dispersed phase: In the colloidal solution colloidal particles constitute dispersed phase.
• Dispersion medium: In the colloidal solution the medium in which colloidal particles are dispersed in called dispersion medium.
• e.g. in the colloidal solution of starch in water, starch particles constitutes dispersed phase and water constitutes dispersion medium.

Question 7.
From the methods (or techniques) of distillation, filtration, fractional distillation, chromatography, crystallisation, select and write down the technique you would use to separate:

1. Constituents of colouring matter in ink.
2. Hydrated copper (II) sulphate or blue vitriol from its aqueous solution.
3. Nitrogen from liquid air.
4. Unused zinc after the reaction of excess of zinc with dilute sulphuric acid.

Answer:

1. Chromatography
2. Crystallisation
3. Fractional distillation
4. Filtration.

Question 8.
Name the technique which could be used to separate:
1. Iodine crystals from sand
2. Petrol from crude oil.
Answer:
1. Iodine crystals can be separated from sand by sublimation.
2. Petrol can be separated from crude oil by fractional distillation.

Question 9.
How will you separate:
1. Pure water from sea water?
2. Kerosene oil from a mixture of kerosene oil and petrol?
Answer:
1. It can be obtained by the process of distillation. When sea water is distilled, water distils, and vapour are condensed in a receiver whereas common salt is left behind in the retort.
2. Kerosene oil can be separated from a mixture of kerosene oil and petrol by fractional distillation when petrol distils off first and then kerosene oil distils off. .

Question 10.

1. Name the kind of change of state when naphthalene changes into gaseous state.
2. Name one element which undergoes similar change as in (i).
3. Name a common substance which exists in all the three states of matter.

Answer:

1. Sublimation
2. Ammonium chloride
3. Water.

Question 11.
Define electrophoresis.
Answer:
Electrophoresis is the process of migration of colloidal particles towards oppositely charged electrode under the influence of an electric field is called electrophoresis. The electrophoresis is due to the charge present on the colloidal particles.

Question 12.
Explain Brownian movement.
Answer:
Brownian movement. When colloidal solutions are viewed with the help of ultra-microscope, it is observed that colloidal particles follow zig-zig path. This is called brownian movement. This effect is due to the unequal impacts of the particles of dispersion medium with colloidal particles.

Question 13.
Explain Tyndall effect.
Answer:
Tyndall effect. If a bright, narrow and convergent beam of light is passed through a colloidal solution and is viewed at right angles with the help of a microscope, the path of light becomes visible and a bright cone of light called Tyndall cone is produced. This luminosity of path of a beam of light in a colloidal solution is called Tyndall effect.

Question 14.
Define physical change and chemical change.
Answer:

• Physical Change. It is a temporary change in which only the physical properties of substances change and it can be easily reversed.
• Examples: Glowing of an electric bulb, evaporation of water.
• Chemical Change: It is a permanent change in which the chemical properties of substances change and there is a change in composition and cannot be reversed.
• Examples: Baking of a cake, Drying of a paint etc.

Question 15.
Classify the following substances into elements, compounds and mixtures:

1. Cane sugar
2. Zinc
3. Oxygen
4. Marble
5. Bronze
6. Nitre
7. Air
8. Milk
9. Iron
10. Stainless steel

Answer:

1. Cane sugar – Compound
2. Zinc – Element
3. Oxygen – Element
4. Marble – Mixture
5. Bronze – Mixture
6. Nitre – Compound
7. Air – Mixture
8. Milk – Mixture
9. Iron – Element
10. Stainless steel – Mixture

Question 16.
1. Name the process used to separate the constituents liquefied air.
2. State how will you remove carbon dioxide from a mixture of carbon dioxide and carbon monoxide.
Answer:
1. Fractional evaporation.
2. Pass the mixture through potassium hydroxide solution. Carbon dioxide is absorbed by KOH solution.
2KOH + C0₂ → K₂C0₃ + H₂0
Carbon monoxide is left behind and is collected over water by downward displacement of water.

Question 17.
How would you separate:
(a) Benzene (b.pt. 80°C) from toluene, methylbenzene (b.pt. 111°C) with which it is miscible?
(b) Kerosene oil from a mixture of kerosene oil and petrol?
(c) Lead sulphate from a mixture of lead sulphate and lead chloride?
Answer:
(a) By using simple distillation when benzene distils off first and its vapours are condensed and collected in a receiver.

(b) Kerosene oil from a mixture of kerosene oil and petrol can be obtained by using separating funnel when kerosene oil forms upper layer.

(c) Lead sulphate from a mixture of lead sulphate and lead chloride can be obtained by boiling with water which dissolves lead chloride and insoluble lead sulphate is separated by filtration.

Question 18.
A molecule can be formed by an element as well as by a compound. Explain.
Answer:
A molecule is the smallest particle of a substance i.e. an element or a compound which can exist freely. It has all the properties of that substance, e.g. a molecule of hydrogen (H₂), a molecule of methane (CH₄).

Question 19.
Can a mixture of chloroform (b.pt. 61°C) and carbon tetrachloride (b.pt. 77°C) be satisfactorily separated by the process you use for separating the various fractions of petroleum?
Answer:
Yes, a mixture of chloroform and carbon tetrachloride can be separated by using fractional distillation as used for the separation of various fractions of petroleum. The heating should be carried out slowly on a sand bath and vapours are condensed in a Liebig condenser and collected in separate receivers.

Question 20.
Name a mixture used:

1. by all living beings
2. in the construction of buildings
3. as a food

Answer:

1. Air
2. Cement
3. Milk

Question 21.
Give two advantages of paper chromatography.
Answer:
1. It can be applied even to a very small amount of the mixture of the substances.
2. The components of a mixture don’t get wasted during separation.

Question 22.
How would you obtain a sample of sulphur from a mixture of sulphur and carbon?
Answer:
Shake the mixture of sulphur and carbon with carbon disulphide and filter. Sulphur will be present in the filtrate and the residue is carbon. The filtrate is evaporated when carbon disulphide vaporises while sulphur is left behind.

Question 23.
How would you obtain pure ammonium chloride when it contains potassium chloride as an impurity?
Answer:
The mixture is heated. Ammonium chloride sublimes and its vapour are condensed in an inverted funnel. Potassium chloride is left behind. From the funnel ammonium chloride is scrapped with a knife.

Question 24.
Name three metals which are liquids at room temperature.
Answer:
These are mercury, cesium and gallium.

Question 25.
Name the various noble gases.
Answer:
The various noble gases are: Helium (He), Neon (Ne), Argon (Ar), Krypton (Kr), Xenon (Xe) and Radon (Rn).

Question 26.
Which of the following statements are correct and which are incorrect?

1. Milk is a mixture.
2. Smoke is a mixture of solids and gases.
3. Ice cream is a mixture.
4. Mercury is a solid
5. Thums up is a homogeneous mixture.

Answer:

1. True
2. True
3. True
4. False
5. True.

Question 27.
If you are given a mixture of hydrogen and carbon dioxide, how would you remove the carbon dioxide gas?
Answer:
The carbon dioxide gas can be removed by passing the gaseous mixture through potassium hydroxide solution which absorbs carbon dioxide and hydrogen gas is set free.

Question 28.
Give two pieces of evidence that sodium chloride is a compound.
Answer:
Sodium chloride is a compound because:
1. in sodium chloride, sodium and chlorine are combined chemically in a fixed ratio by mass.
2. the formation of sodium chloride from sodium and chlorine is accompanied by loss of energy.

Question 29.
Give reasons to show that ammonia is a compound.
Answer:

1. The properties of ammonia are different from those of its components i.e. nitrogen and hydrogen.
2. When ammonia is formed from nitrogen and hydrogen, energy is given out.
3. In ammonia, N and H are present in fixed ratio of 14 : 3 by mass.

Question 30.
Give three reasons why air is considered a mixture and not a compound.
Answer:
In air:

1. the components are not present in any fixed ratio.
2. the properties of air are average of the properties of its components.
3. the components can be separated by physical methods.

Question 31.
Define crystallisation. Give its importance.
Answer:
It is a process in which a pure solid in the form of crystals is separated by cooling its hot saturated solution in a suitable solvent.
Importance:
1. For the purification of salt obtained from sea water.
2. To get crystals of alum from impure samples.

Question 32.
1. Some reduced iron filings and powdered roll sulphur are well mixed and heated in a test tube. Describe all what you observe.
2. Name the grey mass which is formed in test tube at the end of reaction.
3. Would you call the above reaction: exothermic or endothermic?
Answer:
1. When iron filings and powdered roll sulphur are well mixed and heated in a test tube, iron (II) sulphide is produced

2. Grey mass of iron (II) sulphide is produced.
3. The above reaction is endothermic, because heat energy is absorbed.

Question 33.
What are exothermic and endothermic reactions?
Answer:
1. Exothermic reaction: It is a chemical reaction in which heat energy is evolved. e.g. burning of candle.
2. Endothermic reaction: It is a chemical reaction in which heat energy is absorbed e.g. decomposition of calcium carbonate to give calcium oxide and carbon dioxide.

Question 34.
What is the importance of evaporation?
Answer:
It is used to separate the non-volatile component from volatile solvent component from a mixture e.g. dye can be obtained from blue-black ink.

Question 35.
What are the applications of centrifugation?
Answer:

1. It is used in diagnostic laboratories to test blood and urine.
2. It is used in diaries and homes to separate butter from cream.
3. It is used in washing machines to squeeze out water from wet clothes.

Question 36.
How will you separate a mixture of:
(a) Iodine and sand?
(b) Ammonium chloride and common salt?
(c) Chloroform and water?
(d) Carbon disulphide and water?
Answer:
(a) By sublimation
(b) By sublimation
(c) By using a separating funnel
(d) By using a separating funnel.

Question 37.
A solution contains 40 g of NaCl in 320 g of water. Calculate its concentration in terms of mass percentage of solution.
Answer:

• Mass of NaCl = 40g
• Mass of water = 320g
• Total Mass of solution = 40 + 320 = 360g
• Mass percentage of solution = 40 / 360 × 100 = 100 / 9 = 11.1

Question 38.
What are the advantages of crystallisation over evaporation?
Answer:

• Some solids decompose on heating to dryness.
• Some solids like sugar may get charred on heating.
• Some impurities may be present in the solution on dissolving the impure solid in a solvent.

Question 39.
Name the separation technique to separate:

1. Insoluble solid insolvent.
2. Solution of solid in liquid.
3. Miscible mixture of liquids.
4. Immiscible mixture of liquids.
5. Mixture of two solids, one of which sublimes

Answer:

1. Filtration, centrifugation
2. Evaporation, crystallisation, distillation
3. Distillation, fractional distillation
4. Separating funnel
5. Sublimation

Question 40.
What is fractional distillation? Give its importance.
Answer:
Fractional distillation. It is the process of separation of a mixture of two or more miscible liquids having very close boiling points (differing by less than 25°C). In this case, distillation is carried out using a fractionating column.
Importance:
1. This process is ised in the separation of petroleum products.
2. It is used to get component gases from air.

Question 41.
A solution of acetone in water contains 5 ml is 50 ml of its aqueous solution. Calculate the volume percentage of the solution.
Answer:

1. Volume of solute = 8ml
2. Volume of solution = 50ml
3. Volume percentage of solution 5/50 × 100 = 10

Question 42.
Define distillation and give its importance.
Answer:
The conversion of a liquid into vapour and condensing the vapours back into liquid is known as distillation.
Importance:
1. To separate two miscible liquids which boil without decomposition and have sufficient differences in their boiling points (more than 30°C).
2. To separate a volatile component of a solution from a non-volatile component.

Question 43.
How are elements classified?
Answer:
The elements can be classified as:
(a) Metals e.g. Cu, Ag etc.
(b) Non-metals e.g. C, S etc.
(c) Metalloids e.g. As, Sb etc.
(d) Noble gases e.g. He, Ne etc.

Question 44.
Which of the following are pure substances and which are mixtures?

1. Air
2. Milk
3. Graphite
4. Gasoline
5. Distilled water
6. Ice
7. Iodised table salt
8. Diamond
9. Oxygen
10. One rupee coin
11. 22 Carat gold
12. 24 Carat gold
13. Steel
14. Iron
15. Solid Iodine

Answer:

1. Air – Mixture
2. Milk – Mixture
3. Graphite – Pure substance
4. Gasoline – Mixture
5. Distilled water – Pure substance
6. Ice – Pure substance
7. Iodised table salt – Mixture
8. Diamond – Pure substance
9. Oxygen – Pure substance
10. One rupee coin – Mixture
11. 22 carat gold – Mixture
12. 24 carat gold – Pure substance
13. Steel – Mixture
14. Iron – Pure substance
15. Solid Iodine – Pure substance

Question 45.
Which one of the substances given ahead is an element, a mixture or a chemical compound. Give one reason in each case:
(a) chlorine
(b) milk
(c) honey
(d) flowers of sulphur
(e) seawater
(f) gun powder
(g) brine
(h) sulphur
(i) apple juice
(j) carbon dioxide
(k) air
(Z) syrup.
Answer:
(a) Chlorine. It is an element made up of only one kind of atom.
(b Milk. It is a mixture of fat, water etc.
(c )Honey. It is a mixture of carbohydrates.
(d Flowers of sulphur. It is an element made up of only sulphur molecules (S8).
(e )Sea Water. It is a mixture of water and dissolved salts.
(f) Gun powder. It is a mixture of sulphur, nitre and charcoal.
(g) Brine. It is a mixture of water and sodium chloride.
(h) Sulphur. It is an element made up of sulphur molecules (S8).
(i) Apple juice. It is a mixture.
(j) Carbon dioxide. It is a compound of carbon and oxygen combined together in the fixed ratio 3 : 8 by mass.
(k) Air. It is a mixture of oxygen, nitrogen and other gases.
(Z) Syrup. It is a mixture.

Question 46.
(a) Name a chemical technique which could be used successfully to separate
1. Iodine crystals from sand.
2. Petrol from kerosene oil.
(b) A pupil decides to separate powdered calcium carbonate from powdered calcium chloride by shaking the mixture with water and filtering. Would this procedure succeed? Explain your answer.
(c) Mixtures are usually heterogeneous, but sometimes homogeneous also.
Give one example each of two different types of mixtures.
Answer:
(a) 1. Sublimation
2. Fractional distillation
(b) Yes, when a mixture of calcium carbonate and calcium chloride is treated with water, calcium chloride dissolves whereas calcium carbonate does not. It is separated by filtration.
(c) Homogeneous mixture, e.g. Brass is a homogeneous mixture of copper and zinc.
Heterogeneous mixture, e.g. common salt and sand.

Question 47.
From the following techniques:
Distillation, filtration, fractional distillation, chromatography, crystallisation, sublimation, evaporation, decantation, sedimentation. Select the method you will use to separate:
(a) the constituents of the colouring matter of ink.
(b) hydrated CuS04 from its aqueous solution.
(c) Grass stains.
(d) Common salt from sea-water.
(e) Petrol from crude oil.
Answer:
(a) Chromatography
(b) Crystallisation
(c) Chromatography
(d) Evaporation
(e) Fractional distillation.

Question 48.
How will you separate a mixtu funnel? Explain with an activity.
Answer:
Take a clean separating funnel and take a mixture of mustard oil and water in it. Allow it to stand for sometime. On standing, two separate layers appears. The lower layer is of water (heavier) and the upper layer is of mustard oil (lighter).

Open the stop cock of the separating funnel and pour out the lower layer of water carefully. Close the stop cock when the water has been removed. Mustard oil is left in the separating funnel.

Very Short Answer Type Questions:

Question 1.
Define pure substance.
Answer:
It is a material containing particles of only one kind having a definite set of properties.

Question 2.
Define mixture.
Answer:
It is a material obtained by mixing two or more elements and or compounds in any ratio.

Question 3.
How will you separate the components of an aqueous solution of sodium chloride?
Answer:
By simple distillation.

Question 4.
Give two examples of homogeneous mixture.
Answer:
Sodium chloride dissolved in water, sugar dissolved in water.

Question 5.
Give two examples of homogeneous mixtures.
Answer:
Iron filings and common salt, common salt and sulphur.

Question 6.
Is the mixture of oil and water, homogeneous or heterogeneous?
Answer:
Heterogeneous.

Question 7.
What is solution?
Answer:
It is a homogeneous mixture of two or more substances whose composition can be changed within certain fixed limits.

Question 8.
Give examples of solid solution.
Answer:
Brass, Bronze.

Question 9.
Give one example of gaseous solution.
Answer:
Air.

Question 10.
Name the components of Brass.
Answer:
Zinc and copper.

Question 11.
Define solute.
Answer:
It is the component of a solution which is present in small amount and which is dissolved in another component called solvent.

Question 12.
Define solvent.
Answer:
It is the component of solution which is present in large amount and in which solute is dissolved.

Question 13.
Name the solute and solvent in an aqueous solution of sugar.
Answer:
Water-Solvent, Sugar-Solute.

Question 14.
In tincture of Iodine, name solute and solvent.
Answer:
Solute-Iodine, Solvent-Alcohol.

Question 15.
In soda water, name solute and solvent.
Answer:
Solute-Carbon dioxide, Solvent-water.

Question 16.
What is the type of air mixture?
Answer:
Homogeneous.

Question 17.
In air name solute and solvent?
Answer:
Solvent-Nitrogen, Solute-Oxygen and other gases.

Question 18.
What is the size of particles of solutions?
Answer:
Less than lnm (10^-9m).

Question 19.
What is saturated solution?
Answer:
It is a solution in which no more of solute can be dissolved at the given temperature and pressure.

Question 20.
What is unsaturated solution?
Answer:
It is a solution in which more of solute can be dissolved at the given temperature and pressure.

Question 21.
What is the concentration of a solution?
Answer:
It gives us the exact amount of solute dissolved in an exact amount of solvent or solution.

Question 22.
What is a suspension?
Answer:
It is a heterogeneous mixture in which small particles of a solid don’t dissolve but remain suspended in the liquid (or gas).

Question 23.
Why is suspension temporary?
Answer:
This is because components of suspension can be saparated by filtration.

Question 24.
Suspended particles in a suspension can be seen with naked eye, why?
Answer:
This is because their sizes are more than 100 run.

Question 25.
What is Tyndall effect?
Answer:
It is the scattering of light by colloidal particles.

Question 26.
How will you prove that milk is a colloidal solution?
Answer:
It shows Tyndall effect.

Question 27.
What is the size of colloidal particles?
Answer:
1 to 100 nm.

Question 28.
How will you separate colloidal particles from solution?
Answer:
By ultra centrifugation.

Question 29.
When do we don’t use filtration?
Answer:
If the solid particles present in solution have very small sizes and can pass through pores of filter paper.

Question 30.
What is the principle of centrifugation of mixtures?
Answer:
Heavier particles settle down and lighter particles float over them.

Question 31.
Where do we use centrifugal machine?
Answer:
In diagnostic laboratory to study urine and blood, in dairies to separate butter and cream from milk, to squeeze water from clothes in washing machine.

Question 32.
On the basis of what principle, two immiscible liquids can be separated?
Answer:
Based upon density.

Question 33.
How can a mixture of sodium chloride and ammonium chloride separated?
Answer:
By sublimation.

Question 34.
Name four substances which undergo sublimations.
Answer:
Ammonium chloride, comphor, naphthalene, anthracene.

Question 35.
How many colours are mixed in a dye?
Answer:
Two or more colours.

Question 36.
Define chromatography.
Ans.wer:
It is the separation of coloured components of a mixture based upon adsorption.

Question 37.
What are the uses of chromatography?
Answer:
1. To separate components of a dye.
2. To separate colours from natural colours, to separate sugar from urine and to separate medicine from blood.

Question 38.
Which type of liquid mixture solutions can be separated by simple distillation?
Answer:
Liquids having large differences in their boiling points.

Question 39.
Which type of liquid mixture solutions are separated by fractional distillation?
Answer:
Liquids whose boiling points differ by less than 25 K.

Question 40.
Give two examples where fractional distillation is used to separate the components of a mixture.
Answer:
Air, petroleum.

Question 41.
What is the function of glass beads in fractionating column?
Answer:
These provide surface for cooling and condensing vapours.

Question 42.
Which type of mixture air is?
Answer:
It is a homogeneous mixture.

Question 43.
What is the boiling point of oxygen?
Answer:
183°C.

Question 44.
What is the boiling point of Argon.
Answer:
186°C.

Question 45.
What is the boiling point of nitrogen?
Answer:
196°C.

Question 46.
When do we use crystallisation for purification?
Answer:
To purify solids.

Question 47.
How will you get pure copper sulphate?
Answer:
By crystallisation.

Question 48.
Why is crystallisation better than simple distillation?
Answer:
In simple distillation, some substances decompose or are burnt and some impurities are left.

Question 49.
How will you get pure water from sea water?
Answer:
By evaporation and simple crystallisation.

Question 50.
How is alum purified?
Answer:
By crystallisation.

Question 51.
What are the changes during chemical change?
Answer:
Chemical decomposition and change of chemical properties.

Question 52.
Name the type of change of combustion?
Answer:
Chemical change.

Question 53.
How is matter classified on the basis of chemical decomposition?
Answer:
Elements and compounds.

Question 54.
Which French scientist proved that element is a fundamental or basic particle of matter?
Answer:
Antonie Lorentz Lavosier.

Question 55.
Which is the basic unit of matter?
Answer:
Element.

Question 56.
Define an element.
Answer:
It is the smallest particle of an element which can’t be decomposed into still smaller particles by chemical reaction.

Question 57.
How are elements classified?
Answer:
Metals, non-metals and metalloids.

Question 58.
Name the metal which is liquid at room temperature.
Answer:
Mercury.

Question 59.
What is metalloid?
Answer:
It shows the properties of both metals and non-metals.

Question 60.
Give two examples of metalloids.
Answer:
Arsenic, antimony.

Question 61.
Give examples of non-metals.
Answer:
Carbon, hydrogen, oxygen, chlorine, bromine etc.

Question 62.
Give examples for metals.
Answer:
Sodium, potassium, copper, iron, gold, silver etc.

Question 63.
How many elements are known till today?
Answer:
112.

Question 64.
How many elements occur in nature?
Answer:
There are 92 natural elements.

Question 65.
How many elements are gases at room temperature?
Answer:
11.

Question 66.
Name five methods to separate mixtures.
Answer:

1. Filtration
2. Crystallisation
3. Sublimation
4. Evaporation
5. Distillation.

Question 67.
How are sugar crystals separated in a sugar factory?
Answer:
By centrifugation process.

Question 68.
The size of colloidal particals is in the range …………….. .
Answer:
1 to 100 run.

Question 69.
Tyndall effect is shown by ……………. .
Answer:
Colloidal particles.

Question 70.
He and Ne are ……………….. gases.
Answer:
Noble.

Question 71.
FeS + H₂S0₄ → …………..
Answer:
FeS + H₂S0₄ → FeS0₄ + H₂S

Question 72.
In a refinery, petrol is obtained from crude oil by the process of …………… .
Answer:
Fractional distillation

Question 73.
Grass stains are removed from the clothing by using ……………. as solvent.
Answer:
Methylated spirit

Question 74.
Common salt is obtained from sea water by the process of ……………. .
Answer:
Evaporation

Question 75.
When caustic soda solution is added to an aqueous solution of copper sulphate, a blue precipitate of copper hydroxide is obtained. The copper hydroxide can be separated from the mixture by the process of ……………….. .
Answer:
Filtration.

Punjab State Board PSEB 9th Class Science Important Questions Chapter 1 Matter in Our Surroundings Important Questions and Answers.

PSEB 9th Class Science Important Questions Chapter 1 Matter in Our Surroundings

Long Answer Type Questions:

Question 1.
Give important characteristics of solid state.
Answer:
Characteristics of solid state:

1. The solids have definite mass, volume and shape.
2. The particles in a solid state are closely packed and the empty spaces in them are negligible.
3. The solids are rigid.
4. A solid does not undergo a change in shape easily.
5. The solids can have any number of free surfaces.
6. There are large attractive forces between the molecules in a solid.
7. Solids have high densities.
8. A solid always tends to resist any change in its structure.
9. The solids don’t show the property of diffusion.

Question 2.
Give important characteristics of the liquid state.
Answer:
Characteristics of the liquid state:

1. A liquid has a definite mass and volume but no definite shape.
2. A liquid can take the shape of a container.
3. Liquids have only one free surface.
4. The vacant spaces between the molecules of liquid are more as compared to solids.
5. The attractive forces between the molecules in a liquid state are lesser than in the solids.
6. The liquids have lower densities as compared to solids.
7. The liquids show the property of diffusion.
8. On heating a liquid, the molecules of it move apart, hence the liquids can expand on heating.

Question 3.
Give important characteristics of gas.
Answer:
Characteristics of a gas:

1. A gas has definite mass but it has neither definite shape nor definite volume.
2. The gases can occupy the whole space available to them.
3. There are negligible attractive forces between the molecules of a gas.
4. The gases have no free surface.
5. There are large vacant spaces between the molecules of a gas.
6. The gases show the property of diffusion.
7. Gases have very low densities as compared to the solids and liquids.
8. The molecules in a gas have high kinetic energies.
9. There is no effect of gravity on the motion of the molecules of a gas.
10. The gases exert equal pressure in all the directions on the walls of the container.
11. The gases are highly compressible.

Question 4.
Give the main postulates of kinetic theory of matter.
Answer:
The main postulates of kinetic theory of matter are:

1. All matter is made up of a large number of extremely small particles called molecules (sometimes atoms or ions).
2. The molecules are always in a state of rapid random motion.
3. The molecules possess kinetic energy.
4. There are attractive forces between the molecules.
5. The attractive forces between the molecules of same kind are called cohesive forces and the attractive forces between the molecules of different kinds are called adhesive forces.
6. The kinetic energy of the molecules increases with the increase in temperature.
7. As the distance between the molecules increases, the magnitude of attractive forces between the molecules decreases.

Question 5.
Distinguish between solids, liquids and gases.
Answer:
The main points of differences are:

Property	Solid	Liquid	Gss
1. Packing of Particles	Most closely packed	Loosely packed	Large vacant spaces between the particles
2. Energy	Particles have least energy	Particles have higher energies than in solids	Particles have high energies
3. Shape	Definite	Take the shape of the container	Take the shape of container
4. Volume	Definite	Definite	No definite volume
5. Density	High	Low	Very low
6. Compressibility	Not possible easily	More than in solids	High
7. Number of free surfaces	Any number	One	No
8. Rigidity	High	Low	Not rigid
9. Fluidity	Don’t show	Show	Maximum fluidity
10. Intermolecular spaces	Very small	Small	Large
11. Thermal expansion	Very low	More than solids	Very large
12. Interparticle attractive forces	Very large	More than in gases	Negligible

Question 6.
How will you explain the three states of matter on the basis of Kinetic Model?
Answer:
Solid: In solids the constituent particles are closely packed and there are large attractive forces between them. Therefore, the particles have low kinetic energies and can’t move from one position to another but they have only vibratory motion. Hence solids have definite shapes and definite volumes.
Examples: Wood, rock, copper, iron, cement, stone etc.

Liquid: In liquids the molecules have higher kinetic energies, distances between the molecules are more and attractive forces between the molecules are small. Therefore, the molecules of a liquid can move from one position to another within the liquid. Hence the liquid can take the shape of the container. But the volume of the liquid remains fixed because the molecules can’t leave the liquid.
Examples: Alcohol, milk, benzene, kerosene oil, petrol etc.

Gas: In gases, the molecules have high kinetic energies, there are large vacant spaces between the molecules and there are negligible attractive forces between the molecules. Therefore, in gases, molecules can move randomly and occupy the whole space available to them. Hence, they don’t have definite volumes and shapes.
Examples: Hydrogen, oxygen, nitrogen, sulphur dioxide, carbon dioxide etc.

Question 7.
Define the terms given below and answer the questions associated with them.
(a) Sublimation: Which of the following substances sublime?
Ice, mercury, dry ice, iodine.
(b) Solid: Why do not solids diffuse in one another?
(c) Liquid: Why do liquids flow?
(d) Freezing point: What is the freezing point of water?
(e) Gas: Why are gases compressible and show diffusion?
Answer:
(a) Sublimation. It is the process in which a solid directly changes into vapour on heating and on cooling the gas directly changes into solid.
Dry ice and iodine sublime.
(b) Solid. It is that state of matter which has definite mass, volume and shape, e.g. sugar, rubber, table, stone etc.
The solids don’t diffuse because in the solid state the vacant spaces between the molecules are very small and molecules of a solid can’t move from one position to another.
(c) Liquid. A liquid is that state of matter which has definite mass and volume but has no definite shape, e.g. milk, petrol, kerosene oil, water etc. Liquids flow because the attractive forces between the molecules of a liquid are very small and the molecules can freely move within the liquid.
(4) Freezing point. It is the temperature at which a liquid changes into a solid state by giving out heat energy. For example, freezing point of water is 0°C.
(e) Gas. It is defined as that state of matter which has definite mass only but has neither definite shape nor definite volume. For example, carbon dioxide, oxygen, hydrogen, ammonia etc.

Short Answer Type Questions:

Question 1.
What are the necessary conditions for a substance to be a
1. Solid
2. Liquid and
3. Gas?
Answer:
1. Solid: The melting point of a substance is above room temperature at the atmospheric pressure.
2. Liquid: The melting point of the substance is below room temperature and boiling point is above room temperature under atmospheric pressure.
3. Gas: The boiling point of the substance is below room temperature under atmospheric pressure.

Question 2.
What are the two new states of matter in addition to solid, liquid and gases states?
Answer:
These are:
1. Plasma: It is produced in stars at very high temperature.
2. Bose-Einstein condensate: It is formed by cooling a gas of extremely low density to super low temperature.

Question 3.
Heat, light, shadow, love, radio waves are not considered as matter, why?
Answer:
This is because these are massless and do not occupy space.

Question 4.
Solids have definite shapes and volumes, why?
Answer:
This is because:

• The vacant spaces between the constituent particles are very small.
• There are large attraction forces between the constituent particles.

Question 5.
List the factors which affect evaporation.
Answer:
These are:

1. Exposed surface area
2. Temperature
3. Humidity in the air
4. Wind speed.

Question 6.
Why is sponge solid although it can be compressed?
Answer:
This is because sponge has minute holes in which there is entraped air. When it is pressed, the air is expelled out.

Question 7.
Rubber band can change its shape, is it a solid?
Answer:
Rubber band is a solid because it changes its shape under force and return to its original state when the applied force is removed.

Question 8.
Indicate which of the following don’t constitute matter?
Car, truck, heat, light, sound, TV waves, radio waves, cement, love, hate, cotton cloth, rock.
Answer:
Heat, light, sound, TV waves, radio waves, love, hate.

Question 9.
What happens when the vacant spaces between the particles of a liquid decreases? How is this possible?
Answer:
The liquid will change into solid. This is carried out by decreasing the temperature or cooling the liquid.

Question 10.
Why do we observe water droplets on the outer surface of a glass containing ice cold water?
Answer:
This is because water vapour present in air, on coming in contact with glass containing ice-cold water lose energy and get converted into liquid state which appear as water droplets.

Question 11.
Why should we wear cotton clothes in summer?
Answer:
This is because in summer, we perspire more and cotton being a good absorber of water, absorbs the sweat and exposes it to the atmosphere for easy evaporation.

Question 12.
Name the change of state during the following changes:
(a) Drying of wet clothes.
(b) Melting of wax when kept in sunshine.
(c) Melting of ice.
(d) Formation of clouds.
(e) Naphthalene balls become smaller when kept in air.
Answer:
(a) Liquid to gaseous state.
(b) Solid to liquid state.
(c) Solid to liquid state.
(d) Liquid to gaseous state.
(e) Solid to gaseous state.

Question 13.
State your observations in the following cases:
(a) Ammonium chloride is heated in a hard glass test tube.
(b) Carbon dioxide is compressed to 70 times the atmospheric pressure.
Answer:
(a) When ammonium chloride is heated in a hard glass test tube, dense white fumes of ammonium chloride fill the tube and deposit to give a white powder near the mouth of the tube (cooler parts).
(b) When carbon dioxide is compressed to 70 atmospheric pressure, it changes into solid state.

Question 14.
What is the difference between gas and vapour?
Answer:

• A gas is a substance which exists in the gaseous state even at room temperature. e.g. oxygen, hydrogen, nitrogen etc.
• A vapour is a substance which can exist in the gaseous state at a temperature lower than that of its boiling point, e.g. water vapour, iodine vapour etc.

Question 15.
Why does a gas fill the container completely?
Answer:
The molecules in a gas are far apart and are in a state of rapid random motion in all possible directions with very high speeds. They move throughout the container in which they are put. Thus, a gas fills the container completely.

Question 16.
How is the liquid state different from the gaseous state?
Answer:
The liquid state is different from the gaseous state in terms of magnitude of attractive forces between the molecules.

Question 17.
Complete the following statements:
(a) The process of liquid changing into solid is called
(b) The process of gas changing into liquid is called
(c) The process of liquid changing into gas is called
(d) The temperature at which a solid changes into a liquid is called
Answer:
(a) Solidification
(b) Condensation or Liquefaction.
(c) Evaporation
(d) Melting point.

Question 18.
What are the uses of interconversion of matter?
Answer:
The uses of interconversion of matter are:

1. Water is converted into steam by heating. Steam is used to run turbines and to generate electricity.
2. Metals are melted by heating and these molten metals can be converted into alloys and cast into machinery parts.
3. Water can be changed into steam as well as ice. Therefore, in nature, ice (or snow), liquid water and water vapour are available.

Question 19.
Give the important properties on the basis of which the three states of matter can be distinguished.
Answer:
The three states of matter can be distinguished on the basis of shape, volume, compressibility, packing of molecules, number of free surfaces etc.

Question 20.
What is the importance of (a) melting point of solid and (b) boiling point of a liquid?
Answer:
(a) A pure solid has a sharp melting point. The impurities decrease the melting point of a solid. Therefore, melting point is used to check the purity of a solid compound.
(b) A pure liquid has a sharp boiling point. The impurities increase the boiling of liquid. Therefore, boiling point is used to check the purity of a liquid.

Question 21.
Give two differences between boiling and evaporation.
Answer:

Boiling	Evaporation
1. It takes place at a fixed temperature called boiling point of the liquid.	1. It takes place at all temperatures.
2. It is a fast process.	2. It is a slow process.

Question 22.
Name five substances which are solids, five substances which are liquids and five substances which are gaseous at room temperature.
Answer:

• Solids: Iron, copper, silver, glass and wood.
• Liquids: Water, milk, mercury, kerosene oil and petrol.
• Gases: Hydrogen, oxygen, carbon dioxide, nitrogen, helium.

Question 23.
Represent interconversion of states by using a figure.
Answer:

Question 24.
State what is observed when iodine is heated in a test tube as shown below.
Answer:

When some crystals of iodine are heated slowly in a test tube, the shiny grey iodine changes directly into vapour without melting. The vapour deposit as grey particles called sublimate on the upper cooler parts of the tube.

Question 25.
Why do gases have neither a definite shape nor a definite volume?
Answer:
In gases
(a) there are large spaces between the molecules of a gas.
(b) the molecules have high kinetic energies and
(c) there are negligible attractive forces between the molecules of a gas.
Hence the molecules in a gas have random motion. Therefore, gases have neither a definite shape nor a definite volume.

Question 26.
Give an experiment to prove that gases are more compressible as compared to liquids.
Answer:

1. Take a 100 ml syringe and close its nozzle by inserting it in a rubber cork or stopper. Remove the piston from the syringe so that whole of syringe is filled up with air.
2. Apply a little vaseline to the piston and insert the piston. Compress piston and it moves downwards easily.
3. Hence air is compressed to a very small volume.
4. Now fill the syringe with water and repeat the above experiment. The piston moves hardly downwards, indicating that there is a negligible compression in volume.
5. The above experiment indicates that gases are highly compressible as compared to liquids.

Question 27.
Which phenomenon occurs during the following changes:

1. Size of naphthalene balls decreases
2. Wax melts in the sun
3. Drying of wet clothes
4. Formation of clouds.

Answer:

1. Sublimation
2. Fusion
3. Evaporation
4. Condensation.

Very Short Answer Type Questions:

Question 1.
Why do things around our surroundings look different?
Answer:
This is due to different shapes, sizes and textures.

Question 2.
Define matter.
Answer:
Everything in this universe is made up of material which occupies space, has mass and can be judged by any one or more of the known five physical senses is called matter.

Question 3.
Give five examples of matter.
Answer:
Air, food, stove, water, plants.

Question 4.
What are Panch Tatva?
Answer:
Early Indian philosophers classified matter in the form of five basic elements called Panch Tatva.

Question 5.
Name the Panch Tatva?
Answer:
Air, earth, fire, sky and water.

Question 6.
How many basic elements were there according to ancient greek philosophers?
Answer:
Four.

Question 7.
What are the basic elements according to greek philosophers?
Answer:
Earth, fire, air and water.

Question 8.
How do modem day scientists classify matter?
Answer:
Based upon their physical properties and chemical nature.

Question 9.
How is matter produced?
Answer:
It is composed of particles.

Question 10.
Why does a large volume of waier get coloured due to a few crystals of potassium permanganate?
Answer:
This is because a single crystal of pota .sium permanganate is made up of millions of tiny particles.

Question 11.
How small are particles of matter?
Answer:
The particles of matter are very very small beyond our imagination.

Question 12.
What is in between particles of matter?
Answer:
There are vacant spaces between particles of matter.

Question 13.
Why do common salt, sugar and dettol dissolve in water?
Answer:
This is because there are large vacant spaces between the particles of matter.

Question 14.
Why does the smell of lighted incence stick spreads out to a large space?
Answer:
This is because particles of a matter are in motion.

Question 15.
Why does common salt dissolve in water?
Answer:
This is because particles of common salt get into the vacant spaces between particles of water.

Question 16.
How will you check purity of honey?
Answer:
If honey falls into water in a stright line, it is a pure honey.

Question 17.
What is the effect of temperature on the particles?
Answer:
Increase in kinetic energy of particles.

Question 18.
Why are particles of a matter always in motion?
Answer:
This is due to kinetic energy.

Question 19.
Define diffusion.
Answer:
It is the mixing up of particles of two or more substances.

Question 20.
What is the effect of temperature on diffusion?
Answer:
Diffusion becomes faster.

Question 21.
What is the effect of pressure on particles of a matter?
Answer:
Pressure keeps particles of matter together.

Question 22.
What are the different stages of matter based upon physical states?
Answer:
Solid, liquid and gas.

Question 23.
Give three characteristics of solids.
Answer:
The solids have definite masses, volumes and shapes.

Question 24.
What is the effect of applied force on solids?
Answer:
The solids retain their shapes on applying force but they break when a large force is applied on them but they don’t change their shapes.

Question 25.
Rubber band can change its shape when stretched? Is it a solid?
Answer:
It is solid because it changes its shape under force and returns to its original shape when applied force is removed. It breaks when a very large force is applied to it.

Question 26.
Sugar, common salt etc. take the shape of containers although these are solids?
Answer:
This is because the shapes of their crystals do not change.

Question 27.
Why does a rubber can be compressed?
Answer:
This is due to the presence of air in the holes present in it and on compression air is expelled out.

Question 28.
What is liquid?
Answer:
A liquid has a definite mass and volume but has no definite shape.

Question 29.
Due to which property aquatic animals survive in water?
Answer:
This is due to the presence of oxygen dissolved in water.

Question 30.
Name the gas which gets dissolved in water and is necessary for plants.
Answer:
Carbon dioxide.

Question 31.
Which form of matter can diffuse in liquids?
Answer:
Solids, liquids and gases.

Question 32.
Liquids show faster diffusion than solids. Why?
Answer:
This is because in liquids there are more vacant spaces and molecules can move freely.

Question 33.
Out of solids, liquids and gases which show maximum compressibility?
Answer:
Gases.

Question 34.
Which compressed gas is used in automobiles?
Answer:
Compressed natural gas (CNG).

Question 35.
Which gas is used as fuel in houses?
Answer:
Liquified Petroleum Gas (LPG).

Question 36.
The smells of perfume and lighted incense stick spread rapidly, why?
Answer:
This is because there are large vacant spaces between the molecules and the molecules are in motion with very high speeds.

Question 37.
What are the different states of water?
Answer:
These are solid-ice, liquid-water and gas-water vapour.

Question 38.
Give characteristics of solids.
Answer:
The solids are generally hard. They cannot be compressed. They have definite shapes and definite volumes.

Question 39.
Give characteristics of liquids.
Answer:
They have definite volumes but have no definite shapes. They can be compressed slightly. They can flow.

Question 40.
Give characteristics of gases.
Answer:
The gases have neither definite shapes nor volumes. They are highly compressible.

Question 41.
Give four examples each of solids, liquids and gases.
Answer:
Solids: Wood, stove, sugar, common salt.
Liquids: Water, milk, oil, alcohol.
Gases: Oxygen, hydrogen, carbon dioxide.

Question 42.
What is the full form of CNG?
Answer:
Compressed Natural Gas.

Question 43.
Why do solids have definite shapes?
Answer:
This is because vacant spaces between molecules of a solid are very small and there are large attractive forces between them.

Question 44.
Why does a tyre can be inflated with large volume of air?
Answer:
This is because gases can bear high pressure.

Question 45.
Why don’t gases have definite shapes and volumes?
Answer:
This is because there are large vacant spaces between the molecules of a gas and these are in motion.

Question 46.
How many states of water are there?
Answer:
Three.

Question 47.
The temperature at which a solid melts is called?
Answer:
Melting point.

Question 48.
What is the SI unit of temperature?
Answer:
Kelvin.

Question 49.
0°C = ………. K.
Answer:
0°C = 273.16 K.

Question 50.
How is kelvin temperature changed to centigrade temperature?
Answer:
By substracting 273 from it.

Question 51.
How is centigrade temperature changed in kelvin temperature?
Answer:
By adding 273 to it.

Question 52.
Define fusion.
Answer:
The process of conversion of solid into liquid is called fusion.

Question 53.
What is the boiling point of water?
Answer:
373 K (100°C).

Question 54.
Define sublimation.
Answer:
It is the process of direct conversion of solid into gaseous state and back without changing into liquid state.

Question 55.
What is dry ice?
Answer:
Solid carbon dioxide.

Question 56.
What is the unit of pressure?
Answer:
Atmosphere (atm).

Question 57.
What is the SI unit of pressure?
Answer:
Pascal (Pa).

Question 58.
What is normal atmospheric pressure?
Answer:
The atmospheric pressure at sea level is called normal atmospheric pressure. It is taken as 1 atmosphere.

Question 59.
How does a liquid change into vapour without boiling?
Answer:
Due to evaporation.

Question 60.
Give one example of evaporation.
Answer:
Drying of wet clothes in sunlight.

Question 61.
Name the process of conversion of liquid into gaseous state without boiling.
Answer:
Evaporation.

Question 62.
Name the factors which increase rate of evaporation?
Answer:
These are increase in surface area, increase in temperature, decrease in humidity.

Question 63.
Why rate of evaporation increases with the increase in temperature.
Answer:
This is because kinetic energy of particles increases.

Question 64.
Why do clothes dry faster with the increase in speed of wind?
Answer:
This is because water vapour evaporates along with air and amount of water vapour decrease near the surface of clothes.

Question 65.
What is humidity?
Answer:
The amount of moisture present in the air is called humidity.

Question 66.
How is vaporisation related to humidity?
Answer:
With the increase in humidity in air, rate of evaporation decreases.

Question 67.
Why are clothes spread out for drying?
Answer:
This increases surface area and hence rate of evaporation increases.

Question 68.
How is cooling related to evaporation?
Answer:
With the increase in evaporation, cooling increases.

Question 69.
Why should we wear cotton clothes in summer?
Answer:
This is because in summer we perspire more and cotton being a good absorber of water, absorbs the sweat and exposes it to the atmosphere for evaporation which causes cooling.

Question 70.
How are particles present in plasma?
Answer:
In plasma, the particles have high energy and are excited. These particles are present in the form of ionised gas.

Question 71.
Wha is present in florescent tube and neon bulb?
Answer:
Plasma.

Question 72.
Why do sun and stars glow?
Answer:
Due to plasma.

Question 73.
Why is plasma produced in stars?
Answer:
Due to high temperature.

Question 74.
How is BEC produced?
Answer:
It is formed by cooling a gas of extremely low density to super low temperature.

Question 75.
Who were awarded Noble Prize for Bose-Einstein Condensate state?
Answer:
Eric A. Cornell, Wolfgang Ketreley and Carl E. Wieman.

Question 76.
Which website is used to get information regarding fourth and fifth state of matter?
Answer:
www.chem4kids.com.

Question 77.
The phenomenon occuring during drying of wet clothes is
Answer:
Evaporation.

Question 78.
The intennolecular spaces are …………. in solids.
Answer:
Large or maximum.

Question 79.
A vapour on cooling changes into …………. and on further cooling changes into ………… .
Answer:
liquid, solid.

Question 80.
Matter changes from one state to another either by raising the or lowering the …………. .
Answer:
temperature, temperature.

Question 81.
A change in which a solid, on heating, directly changes into …………. state and the …………. on cooling again changes into ………… state is called …………… .
Answer:
gaseous, gas, solid, sublimation.

Question 82.
The intermolecular spaces are in …………… solids and ……………. in gaseous.
Answer:
minimum, maximum.

Punjab State Board Syllabus PSEB 10th Class Science Important Questions Pdf in English Medium and Punjabi Medium are part of PSEB Solutions for Class 10.

PSEB 10th Class Science Important Questions in Punjabi English Medium

• Chapter 1 Chemical Reactions and Equations Important Questions
• Chapter 2 Acids, Bases and Salts Important Questions
• Chapter 3 Metals and Non-metals Important Questions
• Chapter 4 Carbon and its Compounds Important Questions
• Chapter 5 Periodic Classification of Elements Important Questions
• Chapter 6 Life Processes Important Questions
• Chapter 7 Control and Coordination Important Questions
• Chapter 8 How do Organisms Reproduce? Important Questions
• Chapter 9 Heredity and Evolution Important Questions
• Chapter 10 Light Reflection and Refraction Important Questions
• Chapter 11 The Human Eye and The Colourful World Important Questions
• Chapter 12 Electricity Important Questions
• Chapter 13 Magnetic Effects of Electric Current Important Questions
• Chapter 14 Sources of Energy Important Questions
• Chapter 15 Our Environment Important Questions
• Chapter 16 Management of Natural Resources Important Questions

PSEB 10th Class Science Important Questions in Punjabi Medium

• Chapter 1 ਰਸਾਇਣਿਕ ਕਿਰਿਆਵਾਂ ਅਤੇ ਸਮੀਕਰਣਾਂ Important Questions
• Chapter 2 ਤੇਜ਼ਾਬ, ਖਾਰ ਅਤੇ ਲੂਣ Important Questions
• Chapter 3 ਧਾਤਾਂ ਅਤੇ ਅਧਾਤਾਂ Important Questions
• Chapter 4 ਕਾਰਬਨ ਅਤੇ ਉਸਦੇ ਯੋਗਿਕ Important Questions
• Chapter 5 ਤੱਤਾਂ ਦਾ ਆਵਰਤੀ ਵਰਗੀਕਰਨ Important Questions
• Chapter 6 ਜੈਵਿਕ ਕਿਰਿਆਵਾਂ Important Questions
• Chapter 7 ਕਾਬੂ ਅਤੇ ਤਾਲਮੇਲ Important Questions
• Chapter 8 ਜੀਵ ਪ੍ਰਜਣਨ ਕਿਵੇਂ ਕਰਦੇ ਹਨ? Important Questions
• Chapter 9 ਅਨੁਵੰਸ਼ਿਕਤਾ ਅਤੇ ਜੀਵ ਵਿਕਾਸ Important Questions
• Chapter 10 ਪ੍ਰਕਾਸ਼-ਪਰਾਵਰਤਨ ਅਤੇ ਅਪਵਰਤਨ Important Questions
• Chapter 11 ਮਨੁੱਖੀ ਅੱਖ ਅਤੇ ਰੰਗ-ਬਰੰਗਾ ਸੰਸਾਰ Important Questions
• Chapter 12 ਬਿਜਲੀ Important Questions
• Chapter 13 ਬਿਜਲਈ ਧਾਰਾ ਦੇ ਚੁੰਬਕੀ ਪ੍ਰਭਾਵ Important Questions
• Chapter 14 ਊਰਜਾ ਦੇ ਸੋਮੇ Important Questions
• Chapter 15 ਸਾਡਾ ਵਾਤਾਵਰਨ Important Questions
• Chapter 16 ਕੁਦਰਤੀ ਸਾਧਨਾਂ ਦਾ ਪ੍ਰਬੰਧ Important Questions

PSEB 10th Class Science Important Questions in Hindi Medium

• Chapter 1 रासायनिक अभिक्रियाएँ एवं समीकरण Important Questions
• Chapter 2 अम्ल, क्षारक एवं लवण Important Questions
• Chapter 3 धातु एवं अधातु Important Questions
• Chapter 4 कार्बन एवं उसके यौगिक Important Questions
• Chapter 5 तत्वों का आवर्त वर्गीकरण Important Questions
• Chapter 6 जैव प्रक्रम Important Questions
• Chapter 7 नियंत्रण एवं समन्वय Important Questions
• Chapter 8 जीव जनन कैसे करते हैं Important Questions
• Chapter 9 आनुवंशिकता एवं जैव विकास Important Questions
• Chapter 10 प्रकाश-परावर्तन तथा अपवर्तन Important Questions
• Chapter 11 मानव नेत्र तथा रंगबिरंगा संसार Important Questions
• Chapter 12 विद्युत Important Questions
• Chapter 13 विद्युत धारा के चुंबकीय प्रभाव Important Questions
• Chapter 14 ऊर्जा के स्रोत Important Questions
• Chapter 15 हमारा पर्यावरण Important Questions
• Chapter 16 प्राकृतिक संसाधनों का संपोषित प्रबंधन Important Questions

Punjab State Board Syllabus PSEB 12th Class Chemistry Important Questions Pdf in English Medium and Punjabi Medium are part of PSEB Solutions for Class 12.

PSEB 12th Class Chemistry Important Questions in Punjabi English Medium

• Chapter 1 The Solid State Important Questions
• Chapter 2 Solutions Important Questions
• Chapter 3 Electrochemistry Important Questions
• Chapter 4 Chemical Kinetics Important Questions
• Chapter 5 Surface Chemistry Important Questions
• Chapter 6 General Principles and Processes of Isolation of Elements Important Questions
• Chapter 7 The p-Block Elements Important Questions
• Chapter 8 The d-and f-Block Elements Important Questions
• Chapter 9 Coordination Compounds Important Questions
• Chapter 10 Haloalkanes and Haloarenes Important Questions
• Chapter 11 Alcohols, Phenols and Ethers Important Questions
• Chapter 12 Aldehydes, Ketones and Carboxylic Acids Important Questions
• Chapter 13 Amines Important Questions
• Chapter 14 Biomolecules Important Questions
• Chapter 15 Polymers Important Questions
• Chapter 16 Chemistry in Everyday Life Important Questions

Punjab State Board Syllabus PSEB 12th Class Biology Important Questions Pdf in English Medium and Punjabi Medium are part of PSEB Solutions for Class 12

PSEB 12th Class Biology Important Questions in Punjabi English Medium

• Chapter 1 Reproduction in Organisms Important Questions
• Chapter 2 Sexual Reproduction in Flowering Plants Important Questions
• Chapter 3 Human Reproduction Important Questions
• Chapter 4 Reproductive Health Important Questions
• Chapter 5 Principles of Inheritance and Variation Important Questions
• Chapter 6 Molecular Basis of Inheritance Important Questions
• Chapter 7 Evolution Important Questions
• Chapter 8 Human Health and Disease Important Questions
• Chapter 9 Strategies for Enhancement in Food Production Important Questions
• Chapter 10 Microbes in Human Welfare Important Questions
• Chapter 11 Biotechnology: Principles and Processes Important Questions
• Chapter 12 Biotechnology and its Applications Important Questions
• Chapter 13 Organisms and Populations Important Questions
• Chapter 14 Ecosystem Important Questions
• Chapter 15 Biodiversity and Conservation Important Questions
• Chapter 16 Environmental Issues Important Questions

Punjab State Board Syllabus PSEB 12th Class Environmental Education Important Questions Pdf in English Medium and Punjabi Medium are part of PSEB Solutions for Class 12.

PSEB 12th Class Environmental Education Important Questions in Punjabi English Medium

• Chapter 1 ਜੈਵਿਕ ਵਿਭਿੰਨਤਾ / ਜੀਵ ਅਨੇਕਰੂਪਤਾ (ਭਾਗ-1) Important Questions
• Chapter 2 ਜੈਵਿਕ ਵਿਭਿੰਨਤਾ / ਜੀਵ ਅਨੇਕਰੂਪਤਾ (ਭਾਗ-2) Important Questions
• Chapter 3 ਜੈਵਿਕ ਵਿਭਿੰਨਤਾ / ਜੀਵ ਅਨੇਕਰੂਪਤਾ (ਭਾਗ-3) Important Questions
• Chapter 4 ਵਾਤਾਵਰਣੀ ਪ੍ਰਬੰਧਣ (ਭਾਗ-1) Important Questions
• Chapter 5 ਵਾਤਾਵਰਣੀ ਪ੍ਰਬੰਧਣ (ਭਾਗ-2) Important Questions
• Chapter 6 ਵਾਤਾਵਰਣੀ ਪ੍ਰਬੰਧਣ (ਭਾਗ-3) Important Questions
• Chapter 7 ਸਟੱਬਲ ਬਰਨਿੰਗ ਦੀਆਂ ਸਮੱਸਿਆਵਾਂ Important Questions
• Chapter 8 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਵਿਕਾਸ (ਭਾਗ-1) Important Questions
• Chapter 9 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਵਿਕਾਸ (ਭਾਗ-2) Important Questions
• Chapter 10 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਵਿਕਾਸ (ਭਾਗ-3) Important Questions
• Chapter 11 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਖੇਤੀਬਾੜੀ (ਭਾਗ-1) Important Questions
• Chapter 12 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਖੇਤੀਬਾੜੀ (ਭਾਗ-2) Important Questions
• Chapter 13 ਕਾਇਮ ਰਹਿਣਯੋਗ / ਝੱਲਣਯੋਗ / ਟਿਕਾਊ ਖੇਤੀਬਾੜੀ (ਭਾਗ-3) Important Questions
• Chapter 14 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-1) Important Questions
• Chapter 15 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-2) Important Questions
• Chapter 16 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-3) Important Questions
• Chapter 17 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-4) Important Questions
• Chapter 18 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-5) Important Questions
• Chapter 19 ਵਾਤਾਵਰਣੀ ਕਿਰਿਆ (ਭਾਗ-6) Important Questions
• Chapter 20 ਨਸ਼ਾ-ਮਾੜੇ ਪ੍ਰਭਾਵ-II Important Questions

Punjab State Board Syllabus PSEB 12th Class Physics Important Questions Pdf in English Medium and Punjabi Medium are part of PSEB Solutions for Class 12.

PSEB 12th Class Physics Important Questions in Punjabi English Medium

• Chapter 1 Electric Charges and Fields Important Questions
• Chapter 2 Electrostatic Potential and Capacitance Important Questions
• Chapter 3 Current Electricity Important Questions
• Chapter 4 Moving Charges and Magnetism Important Questions
• Chapter 5 Magnetism and Matter Important Questions
• Chapter 6 Electromagnetic Induction Important Questions
• Chapter 7 Alternating Current Important Questions
• Chapter 8 Electromagnetic Waves Important Questions
• Chapter 9 Ray Optics and Optical Instruments Important Questions
• Chapter 10 Wave Optics Important Questions
• Chapter 11 Dual Nature of Radiation and Matter Important Questions
• Chapter 12 Atoms Important Questions
• Chapter 13 Nuclei Important Questions
• Chapter 14 Semiconductor Electronics: Materials, Devices and Simple Circuits Important Questions
• Chapter 15 Communication Systems Important Questions