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Punjab State Board PSEB 10th Class Science Important Questions Chapter 2 Acids, Bases and Salts Important Questions and Answers.

PSEB 10th Class Science Important Questions Chapter 2 Acids, Bases and Salts

Long Answer Type Questions

Question 1.
What do you mean by neutralization reaction? Explain with an experiment.
Answer:
It is a chemical reaction in which acids reacts with base to form salt and water. It is known as neutralization reaction.

Process of neutralization

Experiment: Take a solution of dilute sodium hydroxide in a beaker. Add few drops of phenolphthalein in this solution. Its colour changes to pink. Take a burette filled with dilute hydrochloric acid. Fix it vertically on a stand as shown in Fig. Place a beaker under it. Add the hydrochloric acid slowly to the beaker with the help of burette and go on swirling the beaker slowly. When the colour of solution disappears then stop adding acid to beaker. Now there is no effect of Red to Blue litmus to the solution. Now there is only salt and water in the beaker which is neutral to litmus. This is known as neutralization reaction.

Example:
HCl + NaOH → NaCl + H₂O
Cu(OH)₂ + H₂SO₄ → CuSO₄ + H₂O
HCl + KOH → KCl + H₂O

Question 2.
Write briefly chemical properties of acids.
Answer:
Acids have several chemical properties :
1. Reaction with metals. Acids reacts with active metals. Zinc, Magnesium, Iron, Mangenese etc. reacts with them to produce hydrogen gas.
Zn(s) + dil. H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)
Mg(s) +dil.2HCl(aq) → MgCl2(aq) + H₂(g)
Fe(s) + dil. H₂SO₄ (aq) → FeSO4(aq) + H₂(g)
Mn(s) + dil. HNO₃ (aq) → Mn(NO₃)(aq) + H₂ (g)

2. Reaction with metals carbonate and metal bicarbonate. Acids reacts with metal carbonate and metal bicarbonate to produce C02.
Na₂CO₃ + H₂SO₄ → Na₂SO4 + H₂O + CO₂
NaHCO₃ + HCl → NaCl + H₂O + CO₂
CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂
K₂CO₃ + 2HCl → 2KCl + H₂O + CO₂

3. Reaction with bases. Acids reacts with base to show neutralization. They produce salt.
HCl + NaOH → NaCl + H₂O
HCl + KOH → KCl + H₂O
Cu(OH)₂ + H₂SO₄ → CuSO₄ + H₂O

4. Reaction with sulphites and bisulphites. Acids react with metal sulphite and bisulphite to produce SO₂ gas.
CaSO₃ + H₂SO₄ → CaSO₄ + H₂O +SO₂ (g)
NaHSO₃ + HCl → NaCl + H₂O + SO₂(g)

5. Reaction with metal sulphides and hydrogen sulphides. Acids react with metal various metal sulphide and hydrogen sulphides to produce H₂S gas.
FeS + H₂SO₄ → FeSO₄ + H₂ S(g)

6. Reaction with metal Chlorides. When metal chloride heated with acids the reaction takes place.
NaCl + H₂SO₄ → NaHSO₄ + HCl (g)
NaCl + NaHSO₄ → Na₂SO₄ + HCl (g)

7. Reaction with metal nitrates. Concentration acid reacts with metal nitrate.
NaNO₃ +H₂SO₄ → NaHSO₄ + HNO₃
NaNO₃ + NaHSO₄ → Na₂SO₄ + HNO₃

8. Reaction with metal oxides. Metal oxides reacts with dilute acids to form salts of
Na₂O + 2HNO₃ → 2NaHO₃ + H₂O
CuO + 2HCl → CuCl₂ + H₂O

Question 3.
Write in brief chemical properties of bases/alkalis.
Answer:
Important chemical properties of bases/alkalis are given below :
1. Reaction with metals, Bases react with some metals to produce hydrogen gas.

2. Reaction with air. Some bases react with CO₂ present in air.
2NaOH + CO₂ → Na₂CO₃
2KOH + CO₂ → K₂CO₃

3. Reaction with acids. Bases react with acids to produce salts.
NaOH+ HCl → NaCl + H₂O
Fe(OH)₂ + 2HCl → FeCl₂ + 2H₂O
Ca(OH)₂ + 2HCl → CaCl₂ + 2H₂O

4. Reaction with salts. Salts of copper, iron, Zinc etc. react with bases and produce insoluble metal hydroxides.
ZnSO₄ + 2NaOH → Na₂SO₄ + Zn(OH)₂ ↓
CuSO₄ + 2NH₄OH → (NH₄)₂SO₄ + Cu(OH)₂ ↓
FeCl₃ + 3NaOH → 3NaCl + Fe(OH)₃ ↓

Question 4.
What is the importance of pH in everyday life?
Answer:
pH has very important role in our life :
1. In animal world. Many of the processes in our body occur within the pH range of 7-0 to 7-8. We can survive only in this narrow range. pH value of our blood, tears, saliva is nearly 7-4. Survival will become impossible if this value becomes less than 7-0 or more than 7-8. When pH of rain water decreases from 7-0 to 5-6 or less then it is called acid rain. WThen acid rain flows to the rivers then pH value of river water lowers. Survival of aquatic life in such rivers become difficult.

2. For plants. For healthy growth of plants a specific pH range of soil is required. If soil becomes more basic or acidic, produce badly affected.

3. Digestive system. Our stomach produces HCl, which without harming us help in the digestion of food. Duiing indigestion the stomach produces too much of acid. This causes pain and irritation in the stomach. To get rid of this pain, bases are used which are called antacids. For this weak base like milk of magnesia is used.

4. Tooth decay. If pH value of the mouth is lower than 5-5, then tooth decay begins. Our teeth are made up of calcium phosphate which is hardest substance in our body. It is not soluble in water but starts decaying when pH of the mouth is lower than 5-5. Bacteria present in the mouth produce acids by .degradation of sugar and food particles. To get rid of this we should use basic tooth paste. This will neutralize the acid and tooth decay can be prevented.

5. Relief from insect stings. When some insects sting us, they leave a special type of acid in our body. Bees, ants etc. leave methanoic acid in our body by their sting. To get relief from pain, mild base like baking soda is rubbed on the stung area.

6. Safety from special plants. Plants like nettle have stingging hair. By touching them we feel pain similar to insect sting. This pain is due to methanoic acid. Conventionally, one can get relief by rubbing leaves of dock plant on the stung area.

Short Answer Type Questions

Question 1.
What are indicators? How do indicators are categorized? Explain.
Answer:
Those substances which change their colour in acidic and basic solutions, are called indicators.
Indicators are categorized into two types on the basis of their special properties and characteristics.

1. Indicators which give colour to acids and basic medium.
2. Indicators which give smell to acids and basic medium.

1. Colour giving indicators :
(A) Litmus solution: Litmus solution is purple dye which is obtained from Lichen plant. This is available as red or blue solution and also in the form of litmus paper. Blue litmus turn to red in the presence of acids and Red litmus turns to blue in the presence of basic media. Litmus is neither acidic nor basic by itself.

(B) Turmeric: Turmeric change to red-brown colour in the presence of bases. That is why vegetable stain on the clothes becomes red brown when washed by applying soap which is alkaline.

(C) Phenolphthalein: This is synthetic indicator. It gives pink colour in the presence of bases.

(D) Methyl orange: This is also synthetic indicator. It gives pink colour in the presence of acidic medium and yellow in the presence of bases.

2. Olfactory indicators: Chopped onion, vanilla essence and clove oil change smell in the presence of acids and bases act as olfactory indicators.

Question 2.
What is dilution?
Answer:
When we mix an acid or base with water, the number of H+/OH~ ions per unit volume decreases, it is called dilution. By dilution, acids and bases are ionized.

Question 3.
Give characteristics of acids.
Answer:

• They are sour to taste.
• They turn blue litmus to red.
• Their solution is not like soap solution.
• They produce hydrogen gas when reacts with metals.
• They react with carbonates to produce carbon dioxide.
• Acid react with bases to produce salts and water.

Question 4.
Give four uses of acids in our everyday life.
Answer:

1. Vinegar is used in cooking food and acts as preservative and used in pickles.
2. HCl in our stomach destroys the harmful bacteria, which reach there with our food.
3. Tartaric acid is used to prepare baking soda.
4. Carbonic acid is used in soft drinks.

Question 5.
What are the harmful effects of acids in everyday life?
Answer:

• They can destroy living cells.
• Concentrated acids can badly damage the skin and soft organs.
• These can damage eatables.

Question 6.
Differentiate between strong acids and weak acids.
Answer:

Strong acids	Weak acids
1. These get completely dissolved in water and produce H+ ions and negative ions.	1. These do not completely dissociate into H+ ions and negative ions.
2. Equilibrium is not established.	2. Equilibrium is established between ions and undissociated ions.
3. Example: H2SO4, HNO3.	3. Example: H2CO3, CH3COOH.

Question 7.
Differentiate between strong base and weak base.
Answer:

Strong base	Weak base
1. These get completely dissolved in water to produce OH– ions.	1. These are partially soluble in water.
2. Example: NaOH, KOH	2. Example: Ca(OH)2, Mg(OH)2.

Question 8.
Categorize the following compounds as strong and weak acids and bases,
(i) HCl
(ii) H₂SO₄
(iii) CH₃CHOOH
(iv) HCN
(v) NH₄OH
(vi) H₃PO₄
(vii) NaOH
(viii) Ca(OH)₂
(ix) KOH
(x) H₂CO₃
Answer:

Question 9.
What is the reason for electric conduction in acids? Explain.
Answer:
Acids produce H+ ions. Due to ions acids can conduct electricity. This conduction takes place in water solution.
HCl + H₂O → H₃O + +Cl^–
HNO₃ +H₂O → H₃O+ +NO₃^–

Question 10.
What happens when a base is dissolved in water? Explain it.
Answer:
Bases when dissolved in water give hydroxide OH^– ion. The water-soluble bases are called alkalis.

Question 11.
Why are bases not touched or tasted?
Answer:
Bases have a bitter taste like soaps and are harmful to skin. They are harmful when touched or tasted.

Question 12.
Write uses of alkalies/bases.
Answer:

• These are used to make soap.
• These are used in basic batteries.
• These are used in making antacids.
• Used in Petrol refining and paper industry.
• To remove stains of grease from cloths.
• To make hard water, soft.

Question 13.
Give normal characteristics of bases.
Answer:

• They are bitter to taste.
• They are soapy to touch and are harmful for skin.
• These turn litmus to blue.
• These turn turmeric to red brown colour.
• These react with acids to produce salts and water.
• They turn phenolphthalein solution to pink.

Question 14.
What is difference between alkali and base?
Answer:
Those alkalies which are soluble in water are called bases. This means all bases are alkalies but all alkalies are not bases, e.g. Ferric hydroxide [Fe(OH)3] and cupric hydroxide [Cu(OH)2] are alkalies but are not bases since these are not soluble in water.

Question 15.
What are the sources to get common salt (NaCl)? Explain.
Answer:
We can get common salt from following sources :

• Sea water: A huge amount of salt is dissolved in sea water. Salt in obtained from sea water through salt shallows. Solar heat and air help in the evaporation of sea water. We get salt.
• Mineral salt: Deposits of solid salt are found in many parts of the world. These beds of rock salts were formed when seas of bygone ages dried up. This salt is mined similar to the mining of coal. These rocks are found in Mandi (Himachal Pradesh), Khewra (Pakistan). Due to impurities this salt is brown in colour.
• From Lakes: Salt is obtained from Sambher lake in Rajasthan, great salt lake in America, Lake Elton in Roose etc. This salt in obtained by evaporation.

Question 16.
Write characteristics of common salt.
Answer:

• Colour and state: It is colourless crystalline substance which melts at 820°C.
• Solubility: Salt is soluble in water.
• Effect of heat: On heating salt a cracking sound is produced due to breaking of ‘ salt crystals.
• Hygroscopic: Salt absorb moisture from the air, This is due to presence of magnesium and calcium chloride.

Reaction with sulphuric acid. Salt reacts with concentrated sulphuric acid to produce HCl gas.

Reaction with silver nitrate. Salt reacts with silver nitrate to form white precipitates of silver chloride.
AgNO₃ + NaCl → AgCl + NaNO₃

Question 17.
Give uses of common salt.
Answer:

• Salt is important constituent of our food.
• This is used as preservative in many eatables.
• It is used in soap, pottery industry.
• It is used in making freezing mixture.
• It is used in the preparation of bleaching powder, caustic soda, hydrochloric acid, washing soda, Baking powder etc.

Question 18.
What is chlor-alkali process? Give pictorial representation of the products of this reaction. Give their uses.
Answer:

Important products of chior-alkali process.

When current is passed through aqueous solution of salt gets dissociated and sodium hydroxide is produced. This is known as chlor-alkali process because the products in this reaction are chlorine (chlore) and sodium hydroxide (base)
2NaCl(aq)+ 2H₂O(l) → 2NaOH(aq) + Cl₂(g) + H₂(g)

All these products are very important and useful in industry medicine, home and cosmetics etc. Chlorine and hydrogen are the by products of this process.

Question 19.
How is bleaching powder prepared? Give its common characteristics and uses.
Answer:
Bleaching powder is obtained by the reaction of chlorine with slaked lime.

To manufacture bleaching powder at large scale, we have a special tower there is a hopper at the top of tower, slaked lime is added through this hopper. At the bottom hot air and chlorine gas are blown. Chlorine moves upwards and is absorbed completely by slaked lime and bleaching powder is produced.

Characteristics :

• Bleaching powder is light yellow coloured powder, It has a sharp smell of chlorine.
• It is soluble in water, but not completely.
• It reacts with CO₂ of air and loose its chlorine.
  CaOCl₂ + CO₂ → CaCO₃ + Cl₂
• It reacts with acids
  CaOCl₂ + 2HCl → CaCl₂ + H₂O + Cl₂
  CaOCl₂ +H₂SO₄ → CaSO₄ + H₂O + Cl₂

Uses

• It is used in paper and textile industry.
• Used to disinfect drinking water to make it free from germs.
• It is used to make unshrinkable work.
• It is used for preparing chloroform.
• It acts as oxidising agent.

Question 20.
Write chemical formula for washing soda. When its crystals are open in air, then what happens?
Answer:
Chemical formula for washing soda is Na₂CO₃. 10H₂O. When its crystals are left open in air then due to efforescence nine molecules of water are lost in the air.
Na₂CO₃.10H₂O → Na₂CO₃ .H₂O + 9H₂O

Question 21.
What happens when solution of sodium hydrogen carbonate is heated? Give chemical reaction for the equation.
Answer:
When sodium hydrogen carbonate solution is heated then carbon dioxide gas is produced and sodium carbonate is produced.

Question 22.
What is common name of the compound CaOCl₂? Name the substance which reacts with chlorine to produce bleaching powder?
Answer:
Common name of compounds CaOCl₂ is bleaching powder. The substance which reacts with chlorine to produce bleaching powder is slaked lime [Ca(OH)₂],

Question 23.
If during the preparation of plaster of Paris the process of heating is not controlled then which substance is formed?
Answer:
Temperature should be maintained at 373 K during the preparation of plaster of Paris. If temperature is not controlled then unhydrated calcium sulphate (CaSO₄) is produced which do not have the properties of plaster of Paris. This is known as dead burnt Plaster.

Question 24.
Explain preparation, properties and uses of baking soda (NaHCO₃).
Answer:
Chemical formula for baking soda is NaHCO₃ and its chemical name is sodium bicarbonate. It is formed when CO₂ is passed through aqueous solution of Na2CO₃.
Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃

It can also be prepared from sodium chloride.

Properties: When it is heated it swells and becomes light. On heating it produces CO₂. It is soluble in water.

Uses :

• It is used in the preparation of baking powder.
• It acts as antacid in case of acidity in the stomach.
• It is also used in soda-acid fire extinguishers.

Question 25.
Explain the following processes.
(i) Deliquescence
Answer:
Deliquescence: When some compounds absorb moisture from air and change to solution then this process is called deliquescence.
e.g. common salt is deliquescence.

(ii) Bleach.
Answer:
Bleach: When some gas or compound decolourises something, this is known as bleach, e.g. bleaching powder or chlorine is used for this purpose.

Question 26.
What happens when carbon dioxide is passed through fresh lime water?
Answer:
When carbon dioxide is passsed through fresh lime water in small quantity then insoluble calcium carbonate is formed and colour of lime water turns to milky.

If excess of CO₂ is passed through this solution, calcium carbonate change to soluble bicarbonate and milkiness disappears.

If this solution is heated again, milky colour again appears because calcium bicarbonate again change to calcium carbonate.

Question 27.
What is pH scale? How does it respresent acidic and basic nature of a solution? Represent whole range of pH and [H₃O]⁺.
Answer:
A scale which is used to know the concentration of hydrogen ion in a solution is called pH scale. Here ‘p’ stands for ‘potenz’ a German word which means power. We can measure from zero to 14 on this scale. Zero represents strongest acid, and 14 represents strongest base. pH is such a number which represents acidic or basic nature of a solution. More is the concentration of hydrogen ion in a solution less is its pH value. If a solution is neutral its pH value is 7. If pH is lower than 7 then solution is acidic and if pH is more than 7 then solution is basic. Normally pH can be found by using universal pH indicator paper.

Question 28.
Are salt crystals really dry? Explain.
Answer:
Copper sulphate crystals which seems to be dry contains water of crystallization. These seem to be dry hut are not. When we heat the crystals then this water is removed and colour of salt become white. When salt is made wet its colour again change to blue.

Fixed number of molecules of water present in unit formula of salt is called water of crystallization. In unit formula of copper sulphate, there are five molecules of water. Formula for hydrated copper sulphate is CuSO4. 5H2O. In Na₂CO₃.10H₂O there are 10 molecules of water.

Gypsum is another salt which contains water of crystalization. There are two molecules of water in it.
Its formula is CaSO₄.2H₂O.

Question 29.
How is washing soda prepared? Give its uses.
Answer:
Washing soda (Na₂CO₃.10H₂O) is obtained from sodium chloride. By heating soda, we get sodium carbonate. By recrystallization of sodium carbonate, washing soda is obtained. This is a basic salt.

Sodium carbonate and sodium bicarbonate are useful in several industrial processes.

Uses of washing soda :

• Sodium carbonate is used in glass, soap and paper industry.
• It is used in the manufacturing of sodium compound such as Borax.
• It is used in cleaning agent for domestic purpose.
• It is used to remove permanent hardness of water.

Question 30.
What is efflorescence? Name one compound which shows efflorescence? Explain your answer with an equation.
Answer:
The phenomenon of losing some part of water of cyrstallization into air from a crystal is called efflorescence. This phenomenon takes place on heating or some times spontaneously. Washing soda contain water of crystallization hence its formula is Na₂CO₃. 10H₂O. When it is placed in open then it loose its 9 molecules of water and single hydrate is left.
Na₂CO₃.10H₂O → Na₂CO₃.H₂O + 9H₂O

on heating it looses all of its water.
Na₂CO₃.10H₂O → Na₂CO₃ + 10H₂O

Question 31.
A baker found that a cake prepared by him is small in size and hard. Which constituent, he forgot to add, due to which cake can become soft and big. Give reason.
Answer:
Baker forgot to add baking powder. When baking powder (a mixture of sodium bicarbonate and Tartaric acid) is added to cake and on heating tartaric acid reacts with sodium bicarbonate to produce carbon dioxide. This carbon dioxide makes the cake to swell and cake becomes light. Baker, definitely forgot to add baking powder that is why cake is small and hard.

Question 32.
When bleaching powder is left open in air, then what happens?
Answer:
When bleaching powder is left open in air, then its properties change. C02 present in air reacts with it due to which calcium carbonate and chlorine gas are produced. Properties of bleaching are lost.
CaOCl₂ + CO₂ → CaCO₃ + Cl₂

Question 33.
What are the important uses of bleaching powder?
Answer:

• It is used to bleach cotton cloths, linen and wood pulp.
• It is used to disinfect drinking water and to make it free of germs.
• It is used to make chloroform.
• Unshrinkable wool is prepared using bleaching powder.
• It acts as oxidizing agent in Laboratories and in industry.

Question 34.
Name the compounds used in hospitals for supporting fractured bones in the right position. How is it prepared?
Answer:
The compound used in hospitals for supporting fractured bones in the right position is plaster of paris. It is calcium sulphate hemihydrate (CaSO₄. \(\frac{1}{2}\)H₂O). It is prepared at a temperature of 373 K by heating gypsum.

Question 35.
Write important uses of Plaster of Paris.
Answer:

• It is used in making toys, moulds, ceramic, containers etc.
• It is used for making material for decoration and statues.
• In hospitals it is used by doctors to set fractured bones and by dental doctors for creating mould to make dentures.
• Used in buildings, to give plane look to walls and ceiling.
• Material used by fire fighters.
• It is used to stop leakage of gases in Laboratories.

Question 36.
Many people complaint about gas problem in stomach. What is main reason for this? Why do they use ‘milk of magnesia’ to get relief from this?
Or
What are antacids?
Answer:
A juice is secreted in the stomach which contains enzyme pepsine and hydrochloric acid. Enzyme pepsine is active in acidic medium. When hdyrochloric acid is produced in excess quantity, then we get burning and pain in the stomach, which is known as acidity.

Those substances which are used to neutralize this acid are called antacids. Usually people take a mild base like milk of magnesia for this purpose. It neutralizes the excess acid and provide relief.

Question 37.
Idols and utensils made up of copper and brass become shiny when rubbed with lemon? Why?
Answer:
Idols and utensils made up of copper and brass become dull due to coating of copper oxide. Citric acid present in lemon react with it to form salt, which can be easily washed with water. Brass and copper surface becomes shiny.

Question 38.
For the safety of teeth what type of toothpaste should be used. Why?
Or
How does change in pH-value helps in tooth decay?
Answer:
Bacteria present in mouth produce acid by degradation of sugar and food particles. This reduces the pH value of mouth which causes tooth decay. After foods we should used basic tooth pastes to prevent tooth decay. Mild bases present in it neutralizes the excess acid. This reducing the chances of tooth decay.

Question 39.
What is the remedy for sting of Nettle plant? Write.
Answer:
Nettle is a herbaceous plant found in jungles. Its leaves have stinging hair. These hair cause painful sting if touched accidentally. This pain is due to the secretion of methanoic acid by stinging hair in the body. To get rid of this pain leaves of dock plant are rubbed on the area of sting. Leaves of dock plant have base in them. This plant often grows beside the nettle plant. It neutralizes the acidic effect and gives relief from pain.

Question 40.
What is acidic rain? How is the pH of soil can be measured?
Answer:
Some of the gases like SO₂, SO₃, NO₂ etc. present in the atmosphere gets dissolved in rain water and fall on earth in the from of acid is called acid rain. This corrodes some of the metals and marble.

pH value of soil can be measured by using paper soaked in universal indicator. This way we can know the nature of soil as acidic or basic. When pH value of rain water is less < than 5-6 then it is called acid rain. To know the pH value of soil, it is dissolved in water in a test tube and its filter is tested with universal indicator pH paper.

Question 41.
Is human life possible on venus planet?
Answer:
No, human life is not possible on venus plant the atmosphere of venus is covered with thick white and yellow clouds of sulphuric acid. If there is a rain is presence of water, it will be acidic and the existence of human life will be impossible.

Question 42.
Magnesium is treated with dil. H₂SO₄. The gas evolved is collected as shown below. Name the method used for collection of gas and the gas produced.

Answer:
Downward displacement of water. The gas produced is hydrogen.

Question 43.
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.

Answer:
Fix two nails on a cork and place it in a 100 ml beaker. Connect thses nails to a 6 volt battery through a bulb and switch as shown in the figure.

Pour some aqueous solution of alcohol or aqueous solution of glucose in the beaker so that nails dip in it. Switch on the current. The bulb does not glow indicating that alcohol and glucose don’t dissociate in aqueous solution and hence do not produce H⁺_(aq) ions although they contain hydrogen.

Aqueous solution of alcohol or glucose does not conduct electricity

1 — Cathode
2 — Anode

Question 44.
Observe the figure and answer the following:

(i) What are 1 and 2?
Answer:
1-Soap bubble filled with hydrogen 2-Burning of hydrogen gas with a pop sound

(ii) Write down the reactions taking place in test tube.
Answer:

Question 45.
In the pH paper shown in figure given below, pH of lemon juice is 2.2 and that milk of magnesia is 10. What is its significance?

Answer:

• Lemon justice is acidic because pH is less than 7.
• Milk of magnesia is basic because pH is more than 7.

Question 46.
Which gas is being produced during reaction in the test tube? How does this gas react with Calcium Hydroxide/Lime water?

Answer:
Carbon dioxide (CO₂).

Very Short Answer Type Questions

Question 1.
What makes food sour?
Answer:
Presence of acids.

Question 2.
What is the reason of bitterness?
Answer:
Presence of bases.

Question 3.
What is the reason of acidity in stomach?
Answer:
excess of HCl acid.

Question 4.
What is the effect of acid on litmus?
Answer:
Blue litmus changes to red.

Question 5.
What are olfactory indicators?
Answer:
Some substances which change their smell in acidic or basic medium are called . olfactory indicators.

Question 6.
Give three examples of olfactory indicators.
Answer:
Chopped onions, clove coil, vanilla essence.

Question 7.
Which gas is produced when Zinc reacts with sodium hydroxide?
Answer:
Hydrogen gas.

Question 8.
Which gas is produced when metal carbonates and metal hydrogen carbonates react with acid?
Answer:
Carbon dioxide.

Question 9.
What happens when CO₂ is passed through lime water?
Answer:
Lime water turns milky.

Question 10.
Why milkiness of lime water disappear when excess of CO₂ is passed through it?
Answer:
Due to formation of Ca(HCO₃)₂ which is soluble in water.

Question 11.
Write the name and colour of the compound formed when copper oxide reacts with dilute hydrochloric acid.
Answer:
Blue-green copper chloride.

Question 12.
Which name is used for metal oxide?
Answer:
Alkaline oxide.

Question 13.
What is the nature of non-metal oxide?
Answer:
Acidic nature.

Question 14.
Why does current flow in acids?
Answer:
Due to ions.

Question 15.
Which ion is produced in acidic solution?
Answer:
Hydrogen ion (H+).

Question 16.
What is used to dry, moist gas?
Answer:
Calcium chloride.

Question 17.
How do we represent hydrogen ion?
Answer:
H⁺_(aq) or hydronium ion (HgO⁺).

Question 18.
Which ions is produced by bases in water?
Answer:
Hydroxide (OH^–) ion.

Question 19.
What is base?
Answer:
Alkalies which are soluble in base.

Question 20.
What should we do to dilute an acid?
Answer:
We should add acid to water slowly and not vice versa.

Question 21.
What is dilution?
Answer:
When we add acid or base in water, concentration of ions (HgO⁺/OH^–) per unit volume decreases, this is known as dilution.

Question 22.
What is name of mixture of various indicators?
Answer:
Universal indicator.

Question 23.
What is that which show different colour at different concen-tration of hydrogen ion in a solution?
Answer:
Universal indicator.

Question 24.
What is pH scale?
Answer:
To know the strength of H⁺ ion in a solution a scale is used known as pH scale.

Question 25.
What is p in pH?
Answer:
‘p’ means ‘potenz’.

Question 26.
What is the range of pH scale?
Answer:
0 to 14.

Question 27.
What is pH value of neutral solution?
Answer:
pH value is 7.

Question 28.
If pH value of solution is less than 7, then what does it indicate?
Answer:
Acidic solution.

Question 29.
If pH value of a solution is more than 7, then what does it indicate?
Answer:
Solution is basic.

Question 30.
What is the value on pH scale for lemon juice?
Answer:
Nearly 2.2.

Question 31.
What is the value on pH scale for pure water?
Answer:
7

Question 32.
What is the value on pH scale for milk of magnesia?
Answer:
10.

Question 33.
What is the value on pH scale for sodium hydroxide?
Answer:
Nearly 14.

Question 34.
What is pH range in which our body works?
Answer:
Our body works in the pH range of 7.0 to 7.8.

Question 35.
What is pH value of acid rain?
Answer:
It is less than 5.6.

Question 36.
In which type of river survival of aquatic animals is difficult?
Answer:
When acid rain water flows to the river.

Question 37.
What surrounds the venus planet?
Answer:
Thick white and yellow clouds of sulphuric acid.

Question 38.
Which acid is produced in our stomach?
Answer:
Hydrochloric acid.

Question 39.
What is produced in the stomach when there is indigestion.
Answer:
Excess of HCl.

Question 40.
What is used for treating excess of acid in the stomach?
Answer:
Antacids (mild bases).

Question 41.
When does tooth decay begin?
Answer:
When pH value in less than 5.5.

Question 42.
Teeth are made up of which substance?
Answer:
Calcium phosphate.

Question 43.
Why do we feel pain due to bee sting?
Answer:
Due to acid.

Question 44.
Which substance is applied on the stinging area which gives relief from pain?
Answer:
Weak base like baking soda.

Question 45.
What do the stinging hair of nettle plant secret?
Answer:
Methanoic acid.

Question 46.
What is the remedy for sting of herbaceous plant Nettle?
Answer:
Rub leaves of dock plant.

Question 47.
Which acid is there in vinegar?
Answer:
Acetic acid.

Question 48.
Which acid is there in lemon, orange?
Answer:
Citric acid.

Question 49.
Which acid is in curd and milk?
Answer:
Lactic acid.

Question 50.
What is main source of salt?
Answer:
Sea water.

Question 51.
What is exothermic reaction?
Answer:
Those chemical reactions in which heat is produced.

Question 52.
What is endothermic reaction?
Answer:
Those chemical reactions in which heat in absorbed are called endothermic reactions.

Question 53.
Solid sodium chloride does not conduct electric current, why?
Answer:
In sodium chloride, Na+ and Cl- ions are held together by strong electrostatic forces of attraction and ions can’t move freely. Hence solid sodium chloride does not conduct electric current.

Question 54.
In which state chemical reactions take place easily.
Answer:
Gaseous or liquid state.

Question 55.
What is solute?
Answer:
It is a compound, which in aqueous solution, dissociate into positive and negative ions.

Question 56.
What is a strong electrolyte?
Answer:
A compound which dissociate in water and its dissociation percentage is 30%, is called strong electrolyte.

Question 57.
What is weak electrolyte?
Answer:
A compound which dissociate in water and its dissociation percentage is less than 30% is called weak electrolyte.

Question 58.
Which acids are obtained from animals?
Answer:
Organic acids.

Question 59.
Who gave pH scale and when?
Answer:
pH scale was given by Danish Chemist Soren Sorensen in 1909.

Question 60.
Concentration of which ion is important in every Biological and many industrial processes?
Answer:
Concentration of hydrogen ion.

Question 61.
What is the reason for burn feeling in stomach and chest? How to get rid of this situation?
Answer:
When excess of hydrochloric acid is produced in stomach, then we feel burn feeling in stomach and chest. We can be relieved by taking baking soda.
NaHCO₃ + HCl → NaCl + H₂O + CO₂

Question 62.
What is baking powder?
Answer:
Baking powder is a mixture of baking soda and tartaric acid.

Question 63.
If we do not use tartaric acid in baking powder for making a cake. How will the cake taste?
Answer:
It will be bitter due to sodium carbonate.

Question 64.
Which chemicals are used in fire extinguishers?
Answer:
Sodium hydrogen carbonate and sulphuric acid.

Question 65.
Which gas is produced in soda acid fire extinguisher?
Answer:
Carbon dioxide gas.

Question 66.
Which compound is used to make water free of germs?
Answer:
Bleaching powder (CaOCl₂).

Question 67.
Name chemical name of quick lime.
Answer:
Calcium oxide (CaO).

Question 68.
Name the deliquescent present in salt.
Answer:
Magnesium chloride (MgCl₂).

Question 69.
What type of smell is given by bleaching powder?
Answer:
Smell of ehlorme gas.

Question 70.
Sometimes eyes become red after swimming in a swimming pool why?
Answer:
Due to excess of bleaching powder in water.

Question 71.
When did Egyptions used plaster of paris?
Answer:
They used it 5000 years ago.

Question 72.
How did the Egyptions prepare plaster of Paris?
Answer:
They heated Gypsum in open air.

Question 73.
What was the use of Plaster of Paris for Egyptions?
Answer:
They used to fix rocks with it as cement for their monuments.

Question 74.
What is the relation of ‘Paris’ in plaster of Paris?
Answer:
In the beginning Gypsum was obtained from Montmarti in Paris, thus paris is related with it.

Question 75.
What is heated to which temperature from preparing plaster of Paris?
Answer:
Plater of Paris is obtained from gypsum (CaSO₄.2H₂O) by heating it to 373 K.

Multiple Choice Questions:

Question 1.
pH of an acidic solution is:
(A) >7
(B) <7
(C) 7
(D) 14.
Answer:
(B) <7

Question 2.
Neutral solution has pH:
(A) 7
(B) >7
(C) < 7
(D) 14.
Answer:
(A) 7

Question 3.
Common name of NaCO₃. 10H₂O is :
(A) Bleaching powder
(B) Baking powder
(C) Plaster of Paris
(D) Washing soda.
Answer:
(D) Washing soda.

Question 4.
Acid and base react to form salt and water. This reaction is called:
(A) Washing soda.
(B) Chioro-alkali
(C) Reduction
(D) None of these.
Answer:
(D) None of these.

Question 5.
What is used for plastering fractured bones?
(A) Cement
(B) Gypsum
(C) Plaster of Paris
(D) Soda.
Answer:
(C) Plaster of Paris

Question 6.
Toothpaste used for cleaning teeth is :
(A) Acidic
(B) Neutral
(C) Basic
(D) None.
Answer:
(A) Acidic

Question 7.
A solution turns red litmus blue, its pH is :
(A) 1
(B) 4
(C) 5
(D) 10
Answer:
(D) 10.

Fill in the blanks:

Question 1.
The common name of CaOCl₂ is ______
Answer:
Bleaching powder.

Question 2.
The sodium compound used for softening hard water is ______
Answer:
Washing soda.

Question 3.
The common name of Na₂CO₃.10H₂O is ______
Answer:
Washing soda.

Punjab State Board PSEB 10th Class Science Book Solutions Chapter 2 Acids, Bases and Salts Textbook Exercise Questions and Answers.

PSEB Solutions for Class 10 Science Chapter 2 Acids, Bases and Salts

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

Question 1.
A solution turns red litmus blue, its pH is likely to be :
(a) 1
(b) 4
(c) 5
(d) 10.
Answer:
(d) 10.

Question 2.
A solution reacts with crushed egg-shells to give a gas that turns lime- water milky. The solution contains:
(a) NaCl
(b) HCl
(c) LiCl
(d) KC1.
Answer:
(b) HCl

Question 3.
10 mL of a solution of NaOH is found to be completely neutralised by 8 mL of a given solution of HCl. If we take 20 mL of the same solution of NaOH, the amount of HCl solution (the same solution as before) required to neutralise it will be :
(a) 4 mL
(b) 8 mL
(c) 12 mL
(d) 16 mL.
Answer:
(d) 16 mL.

Question 4.
Which one of the following types of medicines is used for treating indigestion?
(a) Antibiotic
(b) Analgesic
(c) Antacid
(d) Antiseptic.
Answer:
(c) Antacid

Question 5.
Write word equations and then balance equations for the reaction taking place when :
(a) dilute sulphuric acid reacts with zinc granules
Answer:
Zinc granules + Dilute sulphuric acid → Zinc sulphate + Hydrogen

(b) dilute hydrochloric acid reacts with magnesium ribbon
Answer:
Magnesium ribbon + Hydrochloric acid → Magnesium chloride + Hydrogen

(c) dilute sulphuric acid reacts with aluminium powder
Answer:
Aluminium powder + Dilute sulphuric acid → Aluminium sulphate + Hydrogen

(d) dilute sulphuric acid reacts with iron filings.
Answer:
Iron filings + Dilute sulphuric acid → Iron (II) sulphate + Hydrogen.

Question 6.
Compounds such as alcohols and glucose also contain hydrogen but are not categorised as acids. Describe an activity to prove it.
Answer:
Fix two nails on a cork and place it in a 100 ml beaker. Connect these nails to a 6 volt battery through a bulb and switch as shown in the figure.

Aqueous solution of alcohol or glucose does not conduct electricity

Pour some aqueous solution of alcohol or aqueous solution of glucose in the beaker so that nails dip in it. Switch on the current. The bulb does not glow indicating that alcohol and glucose don’t dissociate in aqueous solution and hence
do not produce H⁺ ions although they (aq)
contain hydrogen.

Question 7.
Why does not distilled water conduct electricity, whereas rainwater does?
Answer:

• Distilled water does not conduct electricity because it contains no ions.
• Rainwater contains ions due to dissolved salts, hence it conducts electric current.

Question 8.
Why do acids not show acidic behaviour in the absence of water?
Answer:
This is because in the absence of water, acids do not dissociate to give hydrogen ions > H⁺_(aq)

Question 9.
Five solutions A, B, C, D and E when tested with universal indicator showed pH as 4, 1, 11, 7 and 9 respectively. Which solution is :
(a) neutral?
(b) strongly alkaline?
(c) strongly acidic?
(d) weakly acidic?
(e) weakly alkaline?
Arrange the pH in increasing order of hydrogen-ion concentration.

Solution	pH	Nature of Solution
A	4	Weakly acidic
B	1	Strongly acidic
C	11	Strongly alkaline
D	7	Neutral
E	9	Weakly alkaline

The increasing order of hydrogen-ion concentration is :
11 < 9 < 7 < 4 < 1 (pH values).

Question 10.
Equal lengths of magnesium ribbons are taken in test tubes A and B. Hydrochloric acid (HCl) is added to test tube A, while acetic acid (CH₃COOH) is added to test tube B. Amount and concentration taken for both the acids are same. In which test tube will the fizzing occur more vigorously and why?
Answer:
Fizzing occurs more vigorous in test tube A as compared to in test tube B. This is because concentration of hydrogen ion, It is more in test tube A than in test tube B, as hydrochloric acid a strong acid and acetic acid (CH₃COOH) is a weak acid.

Question 11.
Fresh milk has a pH of 6. How do you think the pH will change as it turns into curd? Explain your answer.
Answer:
Its pH will decrease due to the production of lactic acid which is acidic in nature.

Question 12.
A milkman adds a very small amount of baking soda to fresh milk.
(a) Why does he shift the pH of the fresh milk from 6 to slightly alkaline?
Answer:
So that the milk is not spoiled readily and medium remains basic.

(b) Why does this milk take a long time to set as curd?
Answer:
Because the lactic acid produced during curding reacts with baking soda.

Question 13.
Plaster of Paris should be stored in a moisture-proof container. Explain why?
Answer:
This is because in presence of moisture, plaster of Paris sets to give a hard mass.

Question 14.
What is a neutralisation reaction? Give two examples.
Answer:
The interaction of an acid with a base to form salt and water is called neutralisation reaction.

Examples :

Question 15.
Give two important uses of washing soda and baking soda.
Answer:
(a) Uses of washing soda :

1. It is used in the manufacture of glass and soap.
2. It is used in the manufacture of borax.

(b) Uses of baking soda :

1. It is used in soda-acid fire extinguisher.
2. It is used for making baking powder.

Science Guide for Class 10 PSEB Acids, Bases and Salts InText Questions and Answers

Question 1.
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
Answer:
Dip red litmus paper in solution repeatedly in each tube.
(a) The tube in which the red litmus paper turns purple contains distilled water.
(b) The tube in which red litmus paper turns blue contains basic solution.
(c) The tube in which red litmus paper remains red contains acidic solution.

Question 2.
Why should curd and sour substances not be kept in brass and copper vessels?
Answer:
Curd and other sour substances contain acids which react with the metal surface of brass and copper vessels to produce toxic compounds which are unfit for consumption.

Question 3.
Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
Answer:
When an acid reacts with metal, generally hydrogen is produced.
e.g. Mg + 2 HCl(Dil) → MgCl₂ + H₂ ↑

Pass this gas (H₂) through soap solution. The soap bubbles filled with the gas will rise up. If a burning splinter is brought near the gas, the bubble will burn with a ‘pop’ sound.

Question 4.
Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
Answer:

CO₂ extinguishes a burning candle.

Question 5.
Why do HCl, HNO₃ etc. show acidic characters in aqueous solutions while solutions of compounds like alcohol and glucose do not show acidic character?
Answer:
HCl, HNO₃ etc undergo dissociation in water to give Hydrogen ions, H⁺_(aq) ions and show acidic characteristics. There are compounds like alcohol and glucose don’t dissociate in water to give hydrogen ions, H⁺_(aq) ions. Hence, they don’t show acidic properties.

Question 6.
Why does an aqueous solution of acid conduct electricity?
Answer:
The aqueous solution of an acid contains ions such as hydrogen ions, H⁺_(aq) and other anions. Hence it conducts electricity.

Question 7.
Why does dry HCl gas not change the colour on the dry litmus paper?
Answer:
This is because dry HCl gas is a covalent compound and it does not undergo dissociation to give hydrogen ions, H⁺_(aq) and hence no change in colour of dry litmus paper.

Question 8.
While diluting an acid, why is it recommended that the acid should be added to water and not water to the acid?
Answer:
The process of dissolving an acid or a base in water is an exothermic process. This is because if water is added to concentrated acid, the heat generated may cause the mixture to splash out and cause burns. The glass container may also break due to excessive local heating.

Question 9.
How is the concentration of hydronium ions (H₃O⁺) affected when a solution of an acid is diluted?
Answer:
The concentration of hydronium ions decreases when a solution of an acid is diluted.

Question 10.
How is the concentration of hydroxide ions [OH^–] affected when excess base is dissolved in a solution of sodium hydroxide?
Answer:
When excess of base is dissolved in a solution of sodium hydroxide, the concentration of OH ions increases.

Question 11.
You have two solutions, A and B. The pH of solution A is 6 and pH of solution B is 8. Which solution has more hydrogen ion concentration? Which of this is acidic and which one is basic?
Answer:
In solution A, [H⁺_(aq)] = 10^-6 M, pH < 7
In solution B, [H⁺_(aq)] = 10^-8 M. pH > 7

∴ Then the solution A has more hydrogen ion concentration.
Solution A is acidic.
Solution B is basic.

Question 12.
What effect does the concentration of H⁺_(aq) ions have on the nature of the solution?
Answer:

• If [H⁺] < 10^-7 M, it is basic solution.
• If [H⁺] >10^-7 M, it is an acidic solution.
• If [H⁺] = 10^-7 M, it is a neutral aqueous solution.

Question 13.
Do basic solutions also have H⁺_(aq) ions? If yes, then why are these basic?
Answer:
Basic solutions also contain H⁺_(aq) ions. But in basic solutions :
[H⁺_(aq)] < 10^-7 M
and [OH^–] > 10^-7 M
Since [OH^–_(aq)] is more than [H⁺_(aq)], hence these are basic solutions.

Question 14.
Under what soil condition do you think a farmer would treat the soil of his Helds with quick lime (calcium oxide) or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Answer:
If the pH of the soil is less than 7, i.e. it is acidic, the farmer will treat the soil with quick lime, slaked lime, chalk.

Question 15.
What is the common name of the compound CaOCl₂?
Answer:
Bleaching powder.

Question 16.
Name the substance which on treatment with chlorine yields bleaching powder.
Answer:
Dry slaked lime.

Question 17.
Name the sodium compound which is used for softening hard water.
Answer:
Washing soda.

Question 18.
What will happen if a solution of sodium hydrocarbonate is heated? Give the equation of the reaction involved.
Answer:
It decomposes to give sodium carbonate, water and carbon dioxide gas (which is colourless, odourless and turns lime water milky).

Question 19.
Write an equation to show the reaction between Plaster of Paris and water.
Answer:

Punjab State Board PSEB 10th Class Science Important Questions Chapter 1 Chemical Reactions and Equations Important Questions and Answers.

PSEB 10th Class Science Important Questions Chapter 1 Chemical Reactions and Equations

Long Answer Type Questions

Question 1.
How do we write balanced chemical equations?
Answer:
To understand the method to write balanced chemical equation, let us take an example.
Zinc + Sulphuric acid → Zinc sulphate + hydrogen This equation can be written as below
Zn + H₂SO₄ → ZnSO₄ + H₂

Check the number of atoms on both sides of the arrow.

Element	No. of atoms in reactants (LHS)	No. of atoms in products (RHS)
Zn	1	1
H	2	2
S	1	1
0	4	4

In the equation, number of atoms are same on the both sides of the arrow, thus it is balanced chemical equation.
Now let us try to balance the following chemical equation
Fe + H₂O → Fe₃O₄ + H₂

Step I: Make a list of atoms of different elements in the unbalanced equation

Element	No. of atoms in reactants (LHS)	No. of atoms in products (RHS)
Fe	1	3
H	2	2
0	1	4

Step II: Choose a compound with maximum number of atoms for balancing whether it is reactant or product. Choose an element with maximum number of atoms in the choosen compound. On this basis we choose Fe₃O₄ and in it we choose the element oxygen. On the right, there are four atoms of oxygen and on the left only one.

To balance, oxygen atom

Atoms of oxygen	In reactants	In product
(i) initially	1 (In H2O)	4 (In Fe3O4)
(iii) after balancing	1 × 4	4

To equalize the number of atoms, we can not change the formulae of elements and compounds taking part in the reaction e.g. to balance oxygen atoms we can put coefficient ‘4’ and can write 4H20 but we cannot write H204 or (H₂O)₄ or (H₂O₄).

A partially balanced equation will be
Fe + 4H₂O → Fe₃O₄ + H₂
(Partially balanced equation)

Step III: Fe and H are still unbalanced. Choose any one and move ahead. To balance hydrogen atoms, on left side, make number at atoms of hydrogen ‘4’.

Atoms of hydrogen	In reactants	In product
Initially	8 (4 In H2O)	2 (In H2)
After balancing	8	2 × 4

Now equation becomes
Fe + 4 H₂O → Fe₃O₄ + 4H₂

Step IV: Check the above equation and choose third element which still is unbalanced. We will find that only iron is the element, which remains to be balanced.

To balance Fe we take 3 atoms of Fe on the left side.
3Fe + 4 H₂O → Fe₃O₄ + 4H₂

Step V: At the end, let us count the number ofatoms of elements on both sides of the equation
3 Fe + 4H₂O → Fe₃O₄ + 4H₂ (Balanced equation)

Number of atoms of every element on both sides of the equation are equal. Therefore this equation is now balanced. This method of balancing chemical equations is known as hit and trial method because we use smallest integral coefficient to balance the equation.

Step VI: To write the symbols for physical states. There is no information given about the physical state in the above balanced equation.
To make chemical equation more informative, write the physical states with the reactants and products. To represent the states of solid, liquid, gas, aqueous of the reactants and products we write (s), (l), (g) and (aq) respectively with them. When reactant or product is present in the form of solution in water then word (aq) is written.

Thus, balanced equation will be
3Fe(s) + 4H₂O (g) → Fe₃O₄(s) + 4H₂(g)
when (g) is used with water, then it means that water is used in the form of steam in the reaction. Usually, physical state is not mentioned in the chemical equation until it is very necessary.

Sometimes the conditions of the reaction like temperature, pressure, catalyst etc. are shown over or under the arrow e.g.

Question 2.
Give types of chemical reactions with examples.
Answer:
The various types of chemical reactions are :
1. Combination reactions: In these reactions two or more than two reactants combine to form a single product. Such reactions are known as combination reactions.

Example: Calcium oxide reacts with water to form calcium hydoxide (slaked lime) and a lot of heat is evolved.

In this reaction calcium oxide and water combine to give single product calcium hydroxide.

2. Dissociation or Decomposition reactions: In these reactions single reactant breaks into two or more than two new substances. Such reactions are called dissociation reactions.

Examples of dissociation reaction :

3. Displacement reactions: When an element displaces another element from a compound, then it is called displacement reaction.

Examples:

4. Double displacement reactions. In such a reaction two different atoms or group of atoms exchange themselves with each other.

Example :

Question 3.
Briefly describe oxidation and reduction with suitable examples.
Answer:
Oxidation. Oxidation of a substance takes place in a reaction when there is gain of oxygen or loss of hydrogen in it and opposite to it reduction takes places when there is loss of oxygen or gain of hydrogen.

Example: A black coating of copper (II) oxide is seen on copper powder. Why this black substance is formed?
This copper oxide is formed due to combination of copper with oxygen.

If on this heated substance hydrogen gas is allowed to flow, this black coloured coating changes into brown colour because in these circumstances reverse reaction takes place and copper is again obtained.

When there is gain of oxygen in a substance in a reaction we say oxidation of the substance has taken place and when there is loss of oxygen we say reduction of the substance has taken place.

There is loss of oxygen in copper (II) oxide, therefore it gets reduced. There is gain of oxygen in hydrogen, therefore it is oxidized. Thus, in a reaction one of the reactant is oxidized and other reactant is reduced. Such type of reactions are called reduction-oxidation reactions or redox reactions.

Other examples of redox reaction are :

• ZnO + C → Zn + CO
• MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
• In this reaction carbon is oxidized to become CO and ZnO is reduced to Zn.
• In this reaction HCl is oxidized to Cl₂ and MnO₂ is reduced to MnCl₂.

Question 4.
Balance the following chemical equations.
(i) H₂ + N₂ → NH₃
Answer:
3H₂ + N₂ → 2NHg

(ii) BaCl₂ + Al₂(SO₄)₃ → AlCl₃ + BaSO₄
Answer:
3BaCl₂ + Al₂(SO₄)₂ → 2AlCl₃ + 3BaSO₄

(iii) H₂S + O₂ → SO₂ + H₂O
Answer:
2H₂S + 3O₂ → 2SO₂ + 2H₂O

(iv) KBr + BaI₂ → KI +BaBr₂
Answer:
2KBr + BaI₂ → 2KI + BaBr₂

(v) Al + CuCl₂ → AlCl₃ + Cu
Answer:
2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

(vi) AgNOg + Cu → Cu(NO₃)₂ +Ag
Answer:
2AgNOg + Cu → Cu(NO3)2 + 2Ag

(vii) Al (OH)₃ → Al₂O3 + H₂O
Answer:
2Al(OH)₃ → Al₂O₃ + 3H₂O

(viii) NH₃ + CuO → Cu + N₂ + H₂O
Answer:
2NH₃ + 3CuO → Cu + N₂ + 3H₂O

(ix) KClO₃ → KCl + O₂
Answer:
2KClO₃ → 2KCl + 3O₂

(x) BaCl₂ + K₂SO₄ → 2BaSO₄ + KCl
Answer:
BaCl₂ + K₂SO₄ → BaSO₄ + 2KCl.

Short Answer Type Questions

Question 1.
Give two examples from our daily life to show that chemical changes do take place in our daily life.
Answer:

1. Fermentation of grapes take place.
2. Our body digests the food.
3. In summer, if milk is left in the room, we can see a change in it as it becomes sour.

Question 2.
Differentiate between balanced and skeletal chemical equation.
Answer:
Balanced equation. If number of atoms of each element are same before and after the reaction, then such a reaction is balanced chemical reaction.

Skeletal chemical equation. When number of atoms of each element before and after the reaction are not same then such a chemical equation is called skeletal Chemical equation.

Question 3.
What are the necessary requirements while writing a chemical equation?
Answer:
These are :

• It represents a true chemical change.
• It should be balanced.
• It should represent physical states of the reactants and products.
• It should indicate the necessary conditions required for the reaction to occur.
• It should represent heat changes during reactions.

Question 4.
Give one example each of balanced and skeletal equation.
Answer:
2KCl + O₂ → 2 KCl(s) + 3O₂(g)
This is example of balanced equation.
Zn + AgNO₃(aq) → Zn (NO₃)₂ + Ag
This is example of skeletal equation.

Question 5.
Give chemical formula for slaked lime and one use of it.
Answer:
Chemical formula -Ca(OH)₂. Solution of slaked lime is used for white washing the buildings.

Question 6.
Why there is a shine on the walls after two-three days of white washing?
Answer:
Calcium hydroxide reacts slowly with carbon dioxide present in the air and form a thin layer of calcium carbonate on the walls. After 2-3 days of white wash, calcium carbonate is formed due to which there is a shine on the walls.

Question 7.
Give chemical formula of marble and give reaction to show bow it is formed?
Answer:
Marble is also known as calcium carbonate.
Its chemical formula is CaCO₃ Reaction to show its formation

Question 8.
MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂
How oxidation and reduction in the above reaction is taking place? What is the name of such reaction?
Answer:

Such a reaction is called redox reaction.

Question 9.

Complete the above reaction and tell the colour of the product.
Answer:
Above reaction is :

colour of PbO is yellow.

Question 10.
Give colours of following solutions.
1. FeSO₄
Answer:
FeSO₄ → green

2. CuS04
Answer:
CuSO₄ → blue

Question 11.
What is rusting? What is the chemical formula of rust. What is its loss?
Answer:
New articles made up of iron are shiny but after some time a reddish brown coating is seen on their surface. Usually it is called rusting of iron.

Chemical formula of rust – Fe₂O₃.H₂O (Hydrated iron (III) oxide)
It is powdery substance that gets removed from the surface and due to this iron articles are getting damaged.

Question 12.
Fats are oils containing foods, when kept for long time then what change take place in them? What is name of this process?
Answer:
Fats and oils containing foods, when kept for long time, results in the change of their taste and smell. This process is named as rancidity.

Question 13.
How can we stop rancidity?
Answer:

• To slower down the rate of oxidation, antioxidants are added to food items.
• By keeping food items in air tight containers.
• By flushing nitrogen gas in packets of chips so as to stop the oxidation of chips.

Question 14.
Zinc metal can displace copper from copper sulphate solution. But copper metal can not displace zinc from the solution of Zinc sulphate. Give reason.
Answer:
zinc is more reactive than copper. It can displace copper from copper sulphate solution. Copper is less reactive than zinc thus copper can not displace zinc from zinc sulphate solution.

Question 15.
What happens when zinc rod is placed in copper sulphate solution? Give chemical equation for the reaction.
Answer:
zinc is more reactive than copper. It wall displace copper from solution of copper sulphate and zinc sulphate is formed. Blue colour of the solution of copper sulphate change to white slowly.

Question 16.
What is lime mitigation? Why there is sound of shuun-shuun in this process? Give chemical equation representing the reaction.
Answer:
When quick lime is mixed with water, it changes to slaked lime. This is lime mitigation. This is a exothermic reaction and heat is evolved due to which there is sound of shuun-shuun is produced.

Question 17.
Write names of the substances which got reduced and oxidized.
1. SO₂ + 3H₂S → 2H₃O + 3S
Answer:
In SO₂, S is reduced and in H₂S, S is oxidized.

2. 2Al + 3HCl → 2AlCl₂ + 3H₂
Answer:
Aluminium is reduced and chlorine is oxidized.

3. 2H₂S + SO₂ → 3S + 2H₂O
Answer:
Hydrogen is oxidised and sulphur is reduced.

4. Zn + 2AgNOa → An (NO₃)₂ + 3Ag
Answer:
Zinc is oxidised and silver is reduced.

5. H₂ + CuO → Cu + H₂O.
Answer:
Hydrogen is oxidised and copper is reduced.

Question 18.
What does a complete chemical equation represent and why is it necessary to balance a chemical equation?
Answer:
A complete chemical equation represents reactants, products and their physical state in a symbolic form.
A chemical equation is balanced so that number of atoms of every element in reactants and products becomes equal. Therefore it is necessary to balance the chemical equation.

Question 19.
What type of reactions are combustion of coal and formation of water? Represent by chemical equation.
Answer:
1. Combustion of Coal:
C(s) + O₂ (g) → CO₂ (g)

2. Formation of water from H₂ and O₂ :
2H₂(g) + O₂(g) → 2H₂O(l)

Question 20.
How is dissociation reaction different from combination reaction?
Answer:
In a combination reaction two or more than two substance combine to give a single new substance where as in dissociation reaction a single substance breaks or dissociates into two or more than two new substances.

Question 21.
Give two examples of dissociation reaction.
Answer:

Question 22.
What is the difference between oxidation and reduction?
Answer:
In reaction, some substance gain or loose oxygen and hydrogen. If there is gain of oxygen or loss of hydrogen from a substance then it is called oxidation. Loss of oxygen and gain of hydrogen is called reduction.

Question 23.
Give two examples of corrosion.
Answer:
Examples of corrosion are :

1. black coating on silver
2. green coating on copper.

Question 24.
Which type of reaction is shown in figure given below and define it.
Answer:
Displacement Reaction. It is a reaction in which more active element (metal or non-metal) displaces less active element (metal or non-metal) from its solution of its compound.

Question 25.
What is shown in the figure given ahead? Also indicate 1 and 2 in the figure .
Answer:
The figure represents electro-lysis of water :

1. Oxygen gas
2. Hydrogen gas

Question 26.
The following diagram displays a chemical reaction. Observe carefully and answer the following questions:

(i) Identify the type of chemical reaction.
Answer:
Photochemical decomposition

(ii) Write the chemical equations.
Answer:

Very Short Answer Type Questions

Question 1.
What do we get on the combustion of magnesium ribbon?
Answer:
We get a white powder of Magnesium oxide.

Question 2.
What is law of conservation of mass?
Answer:
In any chemical reaction, mass can neither be created nor destroyed.

Question 3.
Define balanced chemical equation.
Answer:
If number of atoms of each element before and after the chemical reaction are equal, then such a chemical reaction is balanced equation.

Question 4.
Give one example of balanced equation.
Answer:
3 Fe + 4H₂O → Fe₃O₄ + 4H₂.

Question 5.
If (g) is written with water, then what does it represent?
Answer:
Water is in the form of vapour or steam.

Question 6.
Sometimes we show the conditions of a reaction like pressure, temperature, catalyst etc. where do we write it.
Answer:
Above and below the arrow.

Question 7.
How does a new substance form in a chemical reaction?
Answer:
By breaking and making of bonds between atoms.

Question 8.
Define combination reaction.
Answer:
A reaction in which two or more than two reactants combine to give single product is called combination reaction.

Question 9.
What is the use of slaked lime?
Answer:
For whitewashing the buildings.

Question 10.
Write chemical formula for Marble.
Answer:
CaCO₃.

Question 11.
What do we get on the combustion of natural gas?
Answer:
CO₂, H₂O and energy.

Question 12.
Write formula for ferrous sulphate.
Answer:
FeSO₄.7H₂O.

Question 13.
What is formed of grey colour from silver chloride in sun light?
Answer:
Silver metal.

Question 14.

Where is above reaction used?
Answer:
Black and white photography.

Question 15.
Why after some time shining iron articles become dull?
Answer:
Due to rust.

Question 16.
What is the colour of rust coating on iron?
Answer:
Brown colour.

Question 17.
What is corrosion?
Answer:
When a metal comes in contact with moisture, acid etc. it gets corroded and the process is called corrosion.

Question 18.
What is the colour of coating on silver due to corrosion?
Answer:
Black coating.

Question 19.
What is the colour of coating on copper due to corrosion?
Answer:
Green coating.

Question 20.
Due to which process, there is a change in smell and taste of food items which contain fat and oils?
Answer:
This change is due to oxidation and is called rancidity.

Question 21.
What do the manufacturer of chips flush in the packets of chips to prevent oxidation?
Answer:
Nitrogen gas.

Question 22.
What is the colour of coating of copper(II) oxide?
Answer:
Black colour.

Question 23.
What is other name of oxidation-reduction reaction.
Answer:
Redox reaction.

Question 24.
When does oxidation of substance take place in a reaction?
Answer:
When there is gain of O₂ or loss of H₂.

Question 25.
When does reduction of a substance take place in a reaction?
Answer:
When there is loss of O₂ or gain of H₂.

Question 26.
White coloured silver chloride change to which colour in sunlight?
Answer:
In grey colour.

Question 27.
Give one example of endothermic reaction.
Answer:
3AgCl(s) → 2Ag(s) + Cl₂(g)

Question 28.
In w hat calcium carbonate dissociate when heat is given to it?
Answer:
Calcium oxide and carbon dioxide.

Question 29.
Write chemical formula for slaked lime.
Answer:
Ca(OH)₂.

Question 30.
What is special there in potato, rice and bread?
Answer:
Carbohydrate.

Question 31.
What do we get on the decomposition of carbohydrate?
Answer:
Glucose.

Question 32.
Write the reaction for combination of natural gas?
Answer:
CH₄(g) + 2O₂(g) → CO₂(g) + 2H₂O(g) + energy.

Question 33.
What type of reaction is combination of coal and formation of water from H₂ and O₂?
Answer:
Combination reaction.

Question 34.

What is A in above reaction.
Answer:
Chlorophyll.

Question 35.
What is skeletal chemical equation?
Answer:
If in a chemical reaction, number of atoms of each element on left hand side is not equal to number of atoms of each element on right hand side such a reaction is called skeletal chemical equation.

Question 36.
What are products?
Answer:
In a chemical reaction new substances are formed which are known as products.

Question 37.
What are reactants?
Answer:
Those substances which take part in a chemical reaction and undergo chemical changes are called reactants.

Question 38.
What is reduction reaction?
Answer:
It is a reaction in which there is loss of oxygen or gain of hydrogen.

Question 39.
What is oxidation reaction?
Answer:
It is reaction in which there is loss of hydrogen or gain of oxygen.

Question 40.
If in a reaction one reactant is reduced and other is oxidised, what is name of such a reaction?
Answer:
Redox reaction.

Multiple Choice Questions:

Question 1.
The chemical reaction given below represents :
BaCl₂(aq) + Na₂SO₄(aq) →
BaSO₄(s) + 2 NaCl(aq)
(A) Decomposition reaction
(B) Displacement reaction
(C) Combination reaction
(D) Double diplacement reaction.
Answer:
(D) Double displacement reaction

Question 2.
The chemical reaction in which heat energy is given out is called:
(A) Exothermic reaction
(B) Endothermic reaction
(C) Polymerisation reaction
(D) All.
Answer:
(A) Exothermic reaction

Question 3.
During electrolysis, hydrogen and oxygen are produced in the ratio by volume :
(A) 2:1
(B) 1:1
(C) 2:2
(D) 4:1.
Answer:
(A) 2: 1.

Question 4.
The chemical formula of rust is:
(A) Fe₂O₃
(B) FeCO₃
(C) Fe₂O₃ .xH₂O
(D) FeCO₃ xH₂O.
Answer:
(C) Fe₂O₃ .xH₂O

Question 5.
Which is an example of a decomposition reaction?

Answer:

Question 6.
Redox reaction involves:
(A) Oxidation
(B) Reduction
(C) Both oxidation and reduction
(D) None.
Answer:
(C) Both oxidation and reduction

Question 7.
In a packet of chips oxygen is replaced by gas:
(A) CO₂
(B) SO₂
(C) N₂
(D) O₃.
Answer:
(C) N₂

Question 8.
Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)
What type of chemical reaction is shown by the above equation?
(A) Combination reaction
(B) Dissociation reaction
(C) Displacement reaction
(D) Double displacement reaction.
Answer:
(C) Displacement reaction.

Fill in the blanks:

Question 1.
Complete the following chemical equation.

Answer:

Question 2.
Respiration is an ________ reaction.
Answer:
Respiration is an exothermic reaction.

Question 3.
Rusting of iron is a ________ reaction.
Answer:
Rusting iron is a redox reaction.