NCERT Solutions for Class 10 Science Chapter 3 - Chemical Reactions and Equations

Question 1:

Why do we apply paint on iron articles?

Question 2:

Oil and fat containing food items are flushed with nitrogen. Why?

Question 3:

Explain the following terms with one example each:

1. Corrosion
2. Rancidity

Question 4:

Which of the following gases can be used for storage of fresh sample of oil for a long time?

1. Carbon dioxide or helium
2. Carbon dioxide or oxygen
3. Nitrogen or oxygen
4. Helium or nitrogen

Question 5:

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

Question 6:

A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.

1. Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
2. Name the black substance formed and give its chemical formula.

Question 7:

A solution of substance ‘X’ is used for whitewashing.

1. Name the substance ‘X’ and write its formula.
2. Write the reaction of the substance ‘X’ named in (i) above with water.

Question 8:

Why is the amount of gas collected in one of the test tubes in Activity 7 double of the amount collected in the other? Name this gas.

Question 9:

Why does the colour of copper sulphate solution change, when an iron nail is dipped in it?

Question 10:

Give an example of a double displacement reaction other than the one given in Activity 10.

Question 11:

Identify the substances that are oxidised and the substances that are reduced in the following reactions:

1. 4Na(s) + O2(g) → 2Na2O(s)
2. CuO(s) + H2(g) → Cu(s) + H2O(l)

Question 12:

Which of the statements about the reaction below are incorrect?

2PbO(s) + C(s) → 2Pb(s) + CO2(g)

1. Lead is getting reduced.
2. Carbon dioxide is getting oxidised.
3. Carbon is getting oxidised.
4. Lead oxide is getting reduced.

1. (i) and (ii)
2. (i) and (iii)
3. (i), (ii) and (iii)
4. all

Question 13:

Fe2O3 + 2Al → Al2O3 + 2Fe

The above reaction is an example of a

1. combination reaction
2. double displacement reaction
3. decomposition reaction
4. displacement reaction

Question 14:

What does one mean by exothermic and endothermic reactions? Give examples.

Question 15:

Why is respiration considered an exothermic reaction? Explain.

Question 16:

Why are decomposition reactions called opposite of combination reactions? Write equations for these reactions.

Question 17:

Write one equation each for decomposition reactions, in which energy is supplied in the form of heat, light or electricity.

Question 18:

What is the difference between displacement and double displacement reactions? Write equations for both types of reactions.

Question 19:

In the refining of silver, the recovery of silver from silver nitrate solution involves displacement by copper metal. Write down the reaction involved.

Question 20:

What do you mean by precipitation reaction? Explain by giving examples.

Question 21:

Explain the following in terms of gain or loss of oxygen with two examples each:

(a) Oxidation (b) Reduction

Question 22:

A shiny brown coloured element ‘X’ on heating in air becomes black in colour. Name the element ‘X’ and the black coloured compound formed.

Question 23:

The following reaction is an example of a
4NH3(g) + 5O2(g) → 4NO(g) + 6H2O(g)

1. displacement reaction
2. combination reaction
3. redox reaction
4. neutralisation reaction

1. (ii) and (iii)
2. (iii) and (iv)
3. (i) and (iii)
4. (i) and (iv)

Question 24:

Which of the following statements about the given reaction are correct?

3Fe(s) + 4H2O(g) → Fe3O4(s) + 4H2(g)

1. Iron metal is getting oxidised
2. Water is getting reduced
3. Water is acting as reducing agent
4. Water is acting as oxidising agent

1. (ii) and (iv)
2. (i), (ii) and (iv)
3. (iii) and (iv)
4. (i), (ii) and (iii)

Question 25:

Which of the following are exothermic processes?

1. Reaction of water with quick lime
2. Dilution of an acid
3. Evaporation of water
4. Sublimation of camphor (crystals)

1. (i) and (ii)
2. (iii) and (iv)
3. (ii) and (iii)
4. (i) and (iv)

Question 26:

Three beakers labelled as A, B and C, each containing 25 ml of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas in case of beaker C, the temperature of the solution falls, which one of the following statement(s) is(are) correct?

1. In beakers A and B, exothermic process has occurred
2. In beakers A and B, endothermic process has occurred
3. In beaker C exothermic process has occurred
4. In beaker C endothermic process has occurred

1. (ii) only
2. (ii) and (iii)
3. (i) and (iv)
4. (i) only

Question 27:

Which among the following is (are) double displacement reaction(s)?

1. Pb + CuCl2 → PbCl2 + Cu (ii) Na2SO4 + BaCl2 → BaSO4+ 2NaCl
2. C + O2 → CO2 (iv) CH4 + 2O2 → CO2 + 2H2O

1. (i) and (ii)
2. (ii) only
3. (i) and (iv)
4. (iii) and (iv)

Question 28:

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?

1. It is an endothermic reaction
2. It is an exothermic reaction
3. The pH of the resulting solution will be more than seven
4. The pH of the resulting solution will be less than seven

1. (iii) and (iv)
2. (i) and (iv)
3. (i) and (ii)
4. (ii) and (iii)

Question 29:

Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?

1. Displacement reaction
2. Precipitation reaction
3. Combination reaction
4. Double displacement reaction

1. (iv) only
2. (iv) only
3. (ii) only
4. (ii) and (iv)

Question 30:

Electrolysis of water is a decomposition reaction. The molar ratio of hydrogen and oxygen gases liberated during electrolysis of water is:

1. 1 : 2
2. 2 : 1
3. 1 : 1
4. 4 : 1

Question 31:

Which of the following is (are) an endothermic process (es)?

1. Dilution of sulphuric acid
2. Sublimation of dry ice
3. Condensation of water vapour
4. Evaporation of water

1. (iii) only
2. (i) and (iii)
3. only
4. (ii) and (iv)

Question 32:

In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?

1. Ammonium nitrate
2. Lead sulphate (insoluble)
3. Potassium sulphate
4. Lead acetate

Question 33:

The following reaction is used for the preparation of oxygen gas in the laboratory:
2KClO3(s) → 2KCl(s)+ 3O2(g)
Which of the following statement(s) is (are) correct about the reaction?

1. It is a decomposition reaction and endothermic in nature
2. It is a photochemical decomposition reaction and exothermic in nature
3. It is a decomposition reaction and accompanied by the release of heat
4. It is a combination reaction

Question 34:

Which one of the following processes involves chemical reactions?

1. Keeping petrol in a china dish in the open
2. Storing of oxygen gas under pressure in a gas cylinder
3. Liquefaction of air
4. Heating copper wire in presence of air at high temperature

Question 35:

Which of the following are combination reactions?

1. 2KCIO₄ Heat 2KCI + 3O₂
2. MgO + H₂O → Mg(OH)₂
3. 4AI + 3O₂ → 2Al₂O₃
4. Zn + FeSO₄ → ZnSO₄ + Fe

1. (ii) and (iv)
2. (i) and (iii)
3. (iii) and (iv)
4. (ii) and (iii)

Question 36:

Which among the following changes are exothermic or endothermic in nature?

1. Dissolution of ammonium chloride in water
2. Dissolution of sodium hydroxide in water
3. Dilution of sulphuric acid
4. Decomposition of ferrous sulphate

Question 36:

Identify the reducing agent in the following reactions:

1. 2H₂ + O₂ → 2H2O
2. Fe₂O₃ + 3CO → 2Fe + 3CO₂
3. H₂O + F₂ → HF + HOF
4. 4NH₃ + 5O₂ → 4NO + 6H₂O

Question 37:

Identify the oxidising agent (oxidant) in the following reactions:

1. CuO + H₂ Cu + H₂O
2. 3Fe + 4H₂O → Fe₃O₄ + 4H₂
3. V₂O₅ + 5Ca → 2V + 5CaO
4. CuSO₄ + Zn → Cu + ZnSO₄
5. 2Mg + O₂ → 2MgO
6. Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

Question 38:

A solution of potassium chloride when mixed with silver nitrate solution, an insoluble white substance is formed. Write the chemical reaction involved and also mention the type of the chemical reaction.

KCl(aq) + AgNO₃(aq) → KNO₃(aq) + AgCl(s)

Question 39:

Ferrous sulphate decomposes with the evolution of a gas having a characteristic odour of burning sulphur. Write the chemical reaction involved and identify the type of reaction.

2FeSO₄(s) → Fe₂O₃(s) + SO₂(g) + SO₃(g)

Question 40:

A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water it forms a solution which turns red litmus blue. Identify X and also write the chemical reactions involved.

Question 41:

Write the balanced equation for the following chemical reactions:

1. Hydrogen + Chlorine → Hydrogen chloride
2. Barium chloride + Ammonium sulphate → Barium sulphate + Ammonium chloride
3. Sodium + Water → Sodium hydroxide + Hydrogen

Question 42:

Write a balanced chemical equation with state symbols for the following reactions:

1. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
2. Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride and water.

Question 43:

What is a balanced chemical equation? Why should chemical equations be balanced?

Question 44:

Translate the following statements into chemical equations and then balance them:

1. Hydrogen gas combines with nitrogen to form ammonia.
2. Hydrogen sulphide gas burns in air to give water and sulphur dioxide.
3. Barium chloride reacts with aluminium sulphate to give aluminium chloride and a precipitate of barium sulphate.
4. Potassium metal reacts with water to give potassium hydroxide and hydrogen gas.

Question 45:

Balance the following chemical equations:

Question 46:

Write the balanced chemical equations for the following reactions:

1. Calcium hydroxide + Carbon dioxide → Calcium carbonate + Water
2. Zinc + Silver nitrate → Zinc nitrate + Silver
3. Aluminium + Copper chloride → Aluminium chloride + Copper
4. Barium chloride + Potassium sulphate → Barium sulphate + Potassium chloride

Question 47:

Write the balanced chemical equation for the following reactions and identify the type of reaction in each case.

1. Potassium bromide (aq) + Barium iodide (aq) → Potassium iodide (aq) + Barium bromide (s)
2. Zinc carbonate (s) → Zinc oxide (s) + Carbon dioxide (g)
3. Hydrogen (g) + Chlorine (g) → Hydrogen chloride (g)
4. Magnesium (s) + Hydrochloric acid (aq) → Magnesium chloride (aq) + Hydrogen (g)

Question 48:

In which of the following chemical equations, the abbreviations represent the correct states of the reactants and products involved at reaction temperature?

1. 2H₂(g) + O₂(g) → 2H₂O(l)
2. 2H₂(l) + O₂(l) → 2H₂O(g)
3. 2H₂(g) + O₂(l) → 2H₂O(l)
4. 2H₂(g) + O₂(g) → 2H₂O(g)

Question 49:

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case:

1. Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.
2. Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂SO₄.
3. Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
4. Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.

Question 50:

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case:

1. Ethanol is burnt in air to form carbon dioxide and water and releases heat.
2. Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
3. Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
4. Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.

Question 51:

Write the missing components/variables given as x and y in the following reactions:

1. CaCO₃(×) → CaO(s) + CO₂(g)
2. Zn(s) + H₂SO₄(aq) → ZnSO₄(x) + H₂(y)
3. Cu(s) + 2AgNO₃(aq) → Cu(NO₃)2(aq) + x(s)
4. Pb(NO₃)₂(aq) + 2KI(aq) → PbI₂(x) + 2KNO₃(y)

Question 52:

Write the balanced chemical equations for the following reactions:

1. Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu₂I₂), liberates iodine gas and also forms potassium sulphate.
2. Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogen carbonate.
3. Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.

Question 53:

Why do fire flies glow at night?

Question 54:

Write a balanced chemical equation for each of the following reactions and also classify them.

1. Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water.
2. Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
3. A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.
4. Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

Question 55:

Balance the following chemical equations and identify the type of chemical reaction:

1. H₂O₂(l) → H₂O(l) + O₂(g)
2. CaO(s) + SiO₂(s) → CaSiO₃(s)
3. TiCl₄(l) + Mg(s) → Ti(s) + MgCl₂(s)
4. Na(s) + S(s) → Na₂S(s) (e) HgO(s) → Hg(l) + O₂(g)
5. Mg(s) + Cl₂(g) → MgCl₂(s)

Question 56:

A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.

1. Write the chemical formulae of X and Y.
2. Write a balanced chemical equation, when X is dissolved in water.

Question 57:

On heating blue coloured powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X is formed.

1. What could be the pH range of aqueous solution of the gas X?
2. Identify the type of reaction.
3. Identify the brown gas X evolved.
4. Write a balanced chemical equation of the reaction.

Question 59:

What happens when a piece of:

1. silver metal is added to copper sulphate solution? Also, write the balanced chemical equation if the reaction occurs.
2. aluminium metal is added to dilute hydrochloric acid?
3. zinc metal is added to copper sulphate solution?

Question 60:

On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, white precipitate is obtained.

1. Write a balanced chemical equation of the reaction involved.
2. What other name can be given to this precipitation reaction?
3. On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why?

Question 61:

Why should a magnesium ribbon be cleaned before burning in air?

Question 62:

What happens when dilute hydrochloric acid is added to iron filings? Tick the correct answer.

1. Hydrogen gas and iron chloride are produced
2. Chlorine gas and iron hydroxide are produced
3. No reaction takes place
4. Iron salt and water are produced

Question 63:

Which of the following is not a physical change?

1. Dissolution of salt in water
2. Melting of ice to give water
3. Boiling of water to give water vapour
4. Combustion of Liquefied Petroleum Gas (LPG)

Question 64:

A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?

1. KMnO₄ is an oxidising agent, it oxidises FeSO₄
2. KMnO₄ is an unstable compound and decomposes in presence of FeSO₄ to a colourless compound
3. FeSO₄ acts as an oxidising agent and oxidises KMnO₄
4. The colour disappears due to dilution; no reaction is involved

Question 65:

Which among the following statement(s) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to

1. the formation of silver by decomposition of silver chloride
2. sublimation of silver chloride
3. decomposition of chlorine gas from silver chloride
4. oxidation of silver chloride

1. (i) only
2. (iv) only
3. (i) and (iii)
4. (ii) and (iii)

Question 66:

Which among the following are physical or chemical changes?

1. Heating of an iron rod to red hot
2. Burning of Liquefied Petroleum Gas (LPG)
3. Curdling of milk
4. Sublimation of solid ammonium chloride
5. Evaporation of petrol

Question 67:

During the reaction of some metals with dilute hydrochloric acid, following observations were made.

1. Some bubbles of a gas are seen when lead (Pb) is reacted with the acid.
2. The reaction of sodium metal is found to be highly explosive.
3. The temperature of the reaction mixture rises when aluminium (Al) is added.
4. Silver metal does not show any change. Explain these observations giving suitable reactions.

Question 68:

Give the characteristic test for the following gases:
(a) H₂
(b) O₂
(c) SO₂
(d) CO₂