NCERT Exemplar Solutions Class 10 Science Chemical Reactions And Equations

Question 19:  Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.

(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.

(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H₂ SO₄.

(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light. 

Solution 19:

(a) N₂(g)+3H₂(g)= catalyst 773K₂NH₂(g)

It is a combination reaction. 

(b) NaOH(aq)+CH₃COOH(aq)⟶CH₃COONa(aq)+H₂O(l)

It's a reaction in which a heavy base interacts with a weak acid to neutralise it, hence it is a neutralisation reaction. 

(c) C₂H₅OH(aq)+CH₃COOH(l)⟶CH₃COO C₂H₅(aq)+H₂O(t)

It is a neutralisation reaction and double displacement reaction. 

(d) C₂H₄(g)+3O₂(g)→2CO₂(g)+2H₂O(g)+ Heat + Light 

It is an oxidation reaction.

Question 20:  Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.

(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.

(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.

(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat. 

Solution 20:

(a) Fe₂O₃  + 2Al → Al₂O₃(s) + 2Fe (l)

It is Single displacement reaction. 

(b) 3Mg(s) + N₂ → Mg₃N₂

It is Combination reaction. 

(c) Cl₂(g) + 2KI (aq) → 2KCl (Aq) + I₂(s)

It is Single displacement reaction. 

(d) C₂H₅OH + 3O₂ → 2CO₂ + 3H₂O + Heat

It is Combustion reaction.

Question 21:  Complete the missing components/variables given as x and y in the following reactions

(a) Pb(NO₃ )₂ (aq) + 2KI(aq) → PbI₂ (x) + 2KNO₃ (y)

(b) Cu(s) + 2Ag NO₃ (aq) → Cu(NO₃ )₂ (aq) + x(s)

(c) Zn(s) + H₂ SO₄ (aq) → ZnSO₄ (x) + H₂ (y)

(d) CaCO₃ (s) + x →  CaO(s) + CO₂ (g) 

Solution 21:

(a) Pb(NO₃ )₂ (aq) + 2KI(aq) → PbI₂ (s) + 2KNO₃ (aq)

(b) Cu(s) + 2Ag NO₃ (aq) → Cu(NO₃ ) ₂ (aq) + 2Ag(s)

(c) Zn(s) + H₂ SO₄ (aq) → ZnSO₄ (aq) + H₂ (g)

(d) CaCO₃ (s) + Heat → CaO(s) + CO₂ (g)

Question 22:  Which among the following changes are exothermic or endothermic in nature?

(a) Decomposition of ferrous sulphate

(b) Dilution of sulphuric acid

(c) Dissolution of sodium hydroxide in water

(d) Dissolution of ammonium chloride in water 

Solution 22:

(a) Decomposition of ferrous sulphate: Endothermic reaction

(b) Dilution of sulphuric acid: Exothermic reaction

(c) Dissolution of sodium hydroxide in water: Exothermic reaction

(d) Dissolution of ammonium chloride in water: Endothermic reaction

Question 23:  Identify the reducing agent in the following reactions

(a) 4NH₃ + 5O₂ → 4NO + 6H₂O

(b) H₂O + F₂ → HF + HOF

(c) Fe2O₃ + 3CO → 2Fe + 3CO₂

(d) 2H₂ + O₂ → 2H₂O 

Solution 23:

(a) 4NH₃ + 5O₂ → 4NO + 6H₂O

Reducing agent is NH₃ 

(b) H₂O + F₂ → HF + HOF

Reducing agent is F₂ 

(c) Fe2O₃ + 3CO → 2Fe + 3CO₂

Reducing agent is CO 

(d) 2H₂ + O₂ → 2H₂O

Reducing agent is H₂

Question 24:  Identify the oxidising agent (oxidant) in the following reactions

(a) Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

(b) 2Mg + O₂ → 2MgO

(c) CuSO₄ + Zn → Cu + ZnSO₄

(d) V₂O₅ + 5Ca → 2V + 5CaO

(e) 3Fe + 4H₂O → Fe3O₄ + 4H₂

(f) CuO + H₂ → Cu + H₂O 

Solution 24:

(a) Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

Oxidising agent is Pb₃O₄ 

(b) 2Mg + O₂ → 2MgO

Oxidising agent is O₂ 

(c) CuSO₄ + Zn → Cu + ZnSO₄

Oxidising agent is CuSO₄ 

(d) V₂O₅ + 5Ca → 2V + 5CaO

Oxidising agent is V₂O₅ 

(e) 3Fe + 4H₂O → Fe3O₄ + 4H₂

Oxidising agent is H₂O 

(f) CuO + H₂ → Cu + H₂O

Oxidising agent is CuO

Question 25:  Write the balanced chemical equations for the following reactions

(a) Sodium carbonate on reaction with hydrochloric acid in equal molar concentrations gives sodium chloride and sodium hydrogencarbonate.

(b) Sodium hydrogencarbonate on reaction with hydrochloric acid gives sodium chloride, water and liberates carbon dioxide.

(c) Copper sulphate on treatment with potassium iodide precipitates cuprous iodide (Cu₂ I₂ ), liberates iodine gas and also forms potassium sulphate. 

Solution 25:

(a) Na₂CO₃ + HCl → NaCl + NaHCO₃

(b) NaHCO₃ + HCl → NaCl + H₂O + CO₂

(c) 2CuSO₄+4Kl →2K₂SO₄+CU₂I₂+I₂

Question 26:  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 chemical reaction? 

Solution 26:   KCl (aq) + AgNO₃ (aq) → AgCl (s) + KNO₃ (aq)

This is a reaction of double displacement and precipitation.

Question 27:  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. 

Solution 27:   2FeSO₄ → Fe₂O₃ +SO₂+  SO₃

This is a reaction of decomposition.

Question 28:  Why do fireflies glow at night? 

Solution 28:   Fireflies shine at night due to a chemical reaction that occurs within their bodies. In the presence of an enzyme called luciferase, oxygen interacts with calcium, ATP, and luciferin. Bioluminescence is the result of this process.

Question 29:  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? 

Solution 29:   Because of the plant's protective mechanism, grapes on the vine do not ferment. When grapes are plucked from the vine, yeast reacts with them to start the fermentation process. A chemical transition occurs as sugar converts into alcohol.

Question 30:  Which among the following are physical or chemical changes?

(a) Evaporation of petrol

(b) Burning of Liquefied Petroleum Gas (LPG)

(c) Heating of an iron rod to red hot.

(d) Curdling of milk                     

(e) Sublimation of solid ammonium chloride 

Solution 30:  

(a) Evaporation of petrol is Physical change.

(b) Burning of Liquefied Petroleum Gas (LPG) is Chemical change.

(c) Heating of an iron rod to red hot is Physical change.

(d) Curdling of milk is Chemical change.

(e) Sublimation of solid ammonium chloride is Physical change.

Question 31:  During the reaction of some metals with dilute hydrochloric acid, the following observations were made.

(a) Silver metal does not show any change

(b) The temperature of the reaction mixture rises when aluminium (Al) is added.

(c) The reaction of sodium metal is found to be highly explosive

(d) Some bubbles of gas are seen when lead (Pb) is reacted with the acid.

Explain these observations giving suitable reasons. 

Solution 31:

(a) Since silver belongs to the low reactive series of metals, there will be no reaction between it and dilute HCL.

(b) As aluminium (Al) is applied to the reaction mixture, the temperature of the reaction mixture increases since it is an exothermic reaction.

(c) Sodium is a highly reactive metal that forms an exothermic reaction with atmospheric oxygen, resulting in an increase in temperature.

(d) As lead reacts with acid, it creates hydrogen gas, which is what causes bubbles to form.

Question 32:  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. 

Solution 32:  Calcium oxide is Compound X. In the cement industry, calcium oxide is widely used. When CaO is treated with water, it produces Ca(OH)₂, an alkaline compound that changes the colour of red litmus to blue.

Ca + H₂O → Ca(OH)₂                                                                                                                       

Question 33:  Write a balanced chemical equation for each of the following reactions and also classify them.

(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.

(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.  

(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.

(d) Hydrogen sulphide gas reacts with oxygen gas to form solid sulphur and liquid water. 

Solution 33:

(a) Pb(CH₃COO)₂ + 2HCI → PbCl₂ + CH₃COOH

This is a reaction of double displacement.

(b) 2Na + 2C₂H₅OH → 2C₂H₅ONa+ H₂

This is a reaction of displacement.

(c) Fe₂O₃ + 3CO → 2Fe + 3CO₂

This is a reduction-oxidisation reaction.

(d) 2H₂S+O₂ → 2S + 2H₂O

This is a reaction of displacement.

Question 34:  Why do we store silver chloride in dark coloured bottles? 

Solution 34:   As silver chloride is exposed to sunlight, it decomposes into silver and chlorine gas. Consequently Dark-coloured bottles are used to store silver chloride.

Question 35:  Balance the following chemical equations and identify the type of chemical reaction.

(a) Mg (s) + Cl₂ (g) → MgCl₂ (s)

(b) HgO (s) Heat → Hg (l) + O₂ (g)

(c) Na (s) + S (s) → Fuse Na₂S (s)

(d) TiCl₄ (l) + Mg (s) → Ti (s) + MgCl₂ (s)

(e) CaO (s) + SiO₂ (s) → CaSiO₃ (s)

(f) H₂O₂ (l) → H₂O (l) + O₂ (g) 

Solution 35:

(a) Mg (s) + Cl₂(g) → MgCl₂ (s)

A synthesis reaction or a mixture reaction is the name for this form of reaction.

(b) 2HgO (s) — (Heat) → 2 Hg(I) + O₂(g)

This is a thermal decomposition reaction in reality.

(c) 2Na(s) + S(s) — (Fuse) → Na₂S(s)

This is a Combination reaction in nature.

(d) TiCI₄ (l) + Mg(s) → Ti(s) + 2MgCl₂ (s)

This reaction is classified as a displacement reaction.

(e) Cao(s) + SiO₂(s) + CaSiO₃(s)

This is a reaction of synthesis.

(f) 2H₂O₂ (I) — UV → 2H₂O (I) + O₂ (g)

This is a reaction of decomposition.

Question 36:  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.

(a) Write the chemical formulae of X and Y.

(b) Write a balanced chemical equation, when X is dissolved in water. 

Solution 36:  

2Mg + O₂ → 2MgO

(a) Compound X is MgO [Magnesium Oxide]

Compound Y is Mg₃N₂ [Magnesium Nitride]

(b) Magnesium Hydroxide is formed when magnesium oxide is dissolved in water.

MgO  + H₂O → Mg(OH)₂

Question 37:  Zinc liberates hydrogen gas when reacted with dilute hydrochloric acid, whereas copper does not. Explain why? 

Solution 37:   Zinc is more reactive than copper since it is placed above hydrogen in the activity sequence of metals whereas copper is placed below hydrogen. As a consequence, Zinc interacts with HCl, while Copper does not.

Question 38:  A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. 

(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.

(b) Name the black substance formed and gives its chemical formula. 

Solution 38:

(a) Silver combines with H₂S in the atmosphere to form Silver Sulphide, a black-coloured compound. Corrosion is the name for this occurrence.

(b) Silver Sulphide is the dark-coloured substance that results.

2Ag + H₂S → Ag₂S + H₂

Long Answer Questions.............................

Question 39:  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

(a) Write a balanced chemical equation of the reaction.

(b) Identity the brown gas X evolved.

(c) Identify the type of reaction.

(d) What could be the pH range of aqueous solution of the gas X? 

Solution 39:

(b) Nitrogen dioxide, or NO₂, is the brown gas X.

(c) Thermal decomposition is the reaction involved.

(d) Since NO₂ dissolves in water and forms an acidic solution, the pH is 7. (pH range below 7).

Question 40:  Give the characteristic tests for the following gases

(a) CO₂

(b) SO₂

(c) O₂

(d) H₂ 

Solution 40:

(a) CO₂ is injected into limewater, which allows the water to turn milky. This is the carbon-dioxide presence validation measure.

(b) The scent of SO₂, which smells like a rotten egg, is a distinguishing attribute.

(c) An oxygen test involves lighting a match stick near oxygen, which causes it to burn brighter.

(d) When a burning matchstick is brought close to H₂ gas, the flame pops out. This is the procedure used to prove the presence of hydrogen gas.

Question 41:  What happens when a piece of

(a) zinc metal is added to copper sulphate solution?

(b) aluminium metal is added to dilute hydrochloric acid?

(c) silver metal is added to copper sulphate solution?

Also, write the balanced chemical equation if the reaction occurs. 

Solution 41:  

a) As zinc is applied to a copper sulphate solution, copper is displaced and Zinc sulphate is formed.

Zn(s) + CuSo₄₍aq) → ZnSo4(aq) + Cu(s)

b) Aluminium metals react with dilute HCl to form Aluminium Chloride, which creates hydrogen gas.

2Al (s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂

c) There will be no reaction when silver metal is applied to Copper Sulphate solution since silver is a non-reactive metal.

Question 42:  What happens when zinc granules are treated with a dilute solution of H₂SO4, HCl, HNO₃, NaCl and NaOH, also write the chemical equations if a reaction occurs. 

Solution 42:   As zinc granules react with dilute H²SO₄, a displacement reaction occurs, resulting in the formation of ZnSo₄ and the release of H₂

Zn (s) + H₂SO₄ (aq) → ZnSo₄ (aq) +H₂ (g) 

As zinc granules react with diluted HCl, a displacement reaction occurs, resulting in the formation of ZnCl₂ and the release of H₂

Zn (s) + H₂Cl (aq) → ZnCl₂ (aq) + H₂ (g)                                                                            

Zinc granules react with dilute HNO3 to form Zinc nitrate, which creates H₂O and nitrous oxide.

4Zn (s) + 10HNO₃ (aq) → 4Zn(NO₃)₂ (aq) + 5H₂O (i) + N₂O (g) 

There will be no reaction when zinc granules react with NaCl.                            

When Zinc granules react with diluted NaOH solution, resulting in the formation of Na₂ZnO₂ aqueous solution and release of Hydrogen gas will take place.

Zn (s) + NaOH (aq) → Na₂ZnO₂ (aq)  + H₂ (g)

Question 43:  On adding a drop of barium chloride solution to an aqueous solution of sodium sulphite, a white precipitate is obtained.

(a) Write a balanced chemical equation of the reaction involved

(b) What other names can be given to this precipitation reaction?

(c) On adding dilute hydrochloric acid to the reaction mixture, white precipitate disappears. Why? 

Solution 43:

a) When a drop of Barium Chloride solution is applied to an aqueous solution of sodium sulphite, barium sulphite, a white precipitate, is created.

BaCl₂ + Na₂SO₃—>BaSO₃ + 2NaCl

b) The precipitation reaction is a double displacement in this case.

c) Barium chloride, Sulphur dioxide, and water are produced when dilute HCl is added to this reaction mixture. Since barium chloride is a soluble material, it can dissolve the white precipitate.

BaSO₃ + HCl→ BaCl₃ + SO₂ + H₂O

Question 44:  You are provided with two containers made up of copper and aluminium. You are also provided with solutions of dilute HCl, dilute HNO₃, ZnCl₂ and H₂O. In which of the above containers these solutions can be kept? 

Solution 44:   Since copper is a noble metal that does not react with HCl or even HNO₃, these solutions can be stored in a copper jar. Aluminium reacts with acids to form zinc chloride if the solution is stored in an aluminium container.

Copper and aluminium do not react with each other, so water can be contained in either.