Chapter1: Chemical Reactions and Equations

Multiple Choice Questions

1. Which of the following is not a physical change?

(a) Boiling of water to give water vapour

(b) Melting of ice to give water

(c) Dissolution of salt in water

(d) Combustion of Liquefied Petroleum Gas (LPG)

Answer: (d) Combustion of Liquefied Petroleum Gas (LPG)

[ Combustion of Liquefied Petroleum Gas produces new substances, so it is a chemical change, not a physical change.]

2. The following reaction is an example of a

 

(i) displacement reaction    (ii) combination reaction      (iii) redox reaction      (iv) neutralisation reaction

(a) (i) and (iv)      (b) (ii) and (iii)      (c) (i) and (iii)      (d) (iii) and (iv)

Answer:  (c) (ii) and (iii)

[ The given reaction:  is an example of a redox reaction or Combination reaction .]

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

 

 (i) Iron metal is getting oxidised       (ii) Water is getting reduced

(iii) Water is acting as reducing agent    (iv) Water is acting as oxidising agent

(a) (i), (ii) and (iii)    (b) (iii) and (iv)   (c) (i), (ii) and (iv)    (d) (ii) and (iv)

Answer:   (c) (i), (ii), and (iv)

[ The given reaction:

Iron loses electrons (oxidised), water gains electrons (reduced), so water is the oxidising agent. ]

4. Which of the following are exothermic processes?

(i) Reaction of water with quick lime     (ii) Dilution of an acid      (iii) Evaporation of water         (iv) Sublimation of camphor (crystals)

(a) (i) and (ii)     (b) (ii) and (iii)    (c) (i) and (iv)      (d) (iii) and (iv)

Answer:  (a) (i) and (ii).

[ Reaction of water with quick lime (CaO) and dilution of an acid both release heat. Evaporation and sublimation are endothermic.]

5. 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 ?

(i) In beakers A and B, exothermic process has occurred.

(ii) In beakers A and B, endothermic process has occurred.

(iii) In beaker C exothermic process has occurred.

(iv) In beaker C endothermic process has occurred.

(a) (i) only       (b) (ii) only    (c) (i) and (iv)     (d) (ii) and (iii)

Answer:  (c) (i) and (iv)

[ NaOH and anhydrous CuSO₄ dissolution release heat (exothermic), while NaCl dissolution absorbs heat (endothermic), matching the temperature changes observed.]

6. 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?

(a)  is an oxidising agent, it oxidises

(b)  acts as an oxidising agent and oxidises

(c) The colour disappears due to dilution; no reaction is involved

(d)  is an unstable compound and decomposes in presence of  to a colourless compound.

Answer: (a)  is an oxidizing agent; it oxidizes .

[ The correct explanation is that  is an oxidizing agent, and it oxidizes  . The reaction involves the reduction of  and the oxidation of   .]

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

(i) 

(ii)

(iii) 

(iv) 

(a) (i) and (iv)    (b) (ii) only      (c) (i) and (ii)     (d) (iii) and (iv)

Answer:  (b) (ii) only

[ In a double displacement reaction, the positive and negative ions of two ionic compounds exchange places to form two new compounds.

 is a double displacement reaction, and NaCl are the products formed by the exchange of ions.]

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

(i) the formation of silver by decomposition of silver chloride

(ii) sublimation of silver chloride

(iii) decomposition of chlorine gas from silver chloride

(iv) oxidation of silver chloride

(a) (i) only    (b) (i) and (iii)    (c) (ii) and (iii)     (d) (iv) only

Answer: (a) (i) only

[ Sunlight decomposes silver chloride into silver (grey) and chlorine gas. Sublimation, chlorine decomposition, or oxidation are not involved.]

9. 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?

(i) It is an endothermic reaction

(ii) It is an exothermic reaction

(iii) The pH of the resulting solution will be more than seven

(iv) The pH of the resulting solution will be less than seven

(a) (i) and (ii)    (b) (ii) and (iii)    (c) (i) and (iv)   (d) (iii) and (iv)

Answer:  (b) (ii) and (iii)

[ Slaking of lime (CaO + H₂O → Ca(OH)₂) releases heat (exothermic). Ca(OH)₂ is a base, so its solution has pH > 7.]

10. 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?

(i) Displacement reaction    (ii) Precipitation reaction     (iii) Combination reaction     (iv) Double displacement reaction

(a) (i) only     (b) (ii) only     (c) (iv) only     (d) (ii) and (iv)

Answer: (d) (ii) and (iv)

[  
It is a double displacement reaction, and BaSO₄ forms an insoluble precipitate. ]

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

(a) 1:1        (b) 2:1          (c) 4:1           (d) 1:2

Answer: (b) 2:1.

[ Electrolysis of water: . Hydrogen and oxygen are liberated in a 2:1 mole ratio.]

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

(i) Dilution of sulphuric acid        (ii) Sublimation of dry ice      (iii) Condensation of water vapours         (iv) Evaporation of water

(a) (i) and (iii)        (b) (ii) only      (c) (iii) only       (d) (ii) and (iv)

Answer:  (d) (ii) Sublimation of dry ice and (iv) Evaporation of water

[ Sublimation (solid to gas) and evaporation (liquid to gas) absorb heat (endothermic). Dilution of H₂SO₄ and condensation release heat (exothermic).]

13. 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?

(a) Lead sulphate (insoluble)     (b) Lead acetate      (c) Ammonium nitrate     (d) Potassium sulphate

Answer:  (b) Lead acetate

[ Lead acetate is a soluble salt, and when it reacts with aqueous potassium iodide, it will provide lead ions to form lead iodide as a yellow precipitate. Therefore, (b) Lead acetate can be used in place of lead nitrate.]

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

(a) Carbon dioxide or oxygen     (b) Nitrogen or oxygen     (c) Carbon dioxide or helium      (d) Helium or nitrogen

Answer:  (d) Helium or nitrogen

[ Helium and nitrogen are inert gases, and they do not readily react with the oil or contribute to oxidation or degradation. Therefore, using helium or nitrogen is suitable for the long-term storage of a fresh oil sample.]

15. The following reaction is used for the preparation of oxygen gas in the laboratory

Which of the following statement(s) is(are) correct about the reaction?

(a) It is a decomposition reaction and endothermic in nature

(b) It is a combination reaction

(c) It is a decomposition reaction and accompanied by release of heat

(d) It is a photochemical decomposition reaction and exothermic in nature

Answer:  (a) It is a decomposition reaction and endothermic in nature

[ Potassium chlorate breaks into simpler substances on heating, so it is a decomposition reaction and requires heat, making it endothermic. ]

16. Which one of the following processes involve chemical reactions?

(a) Storing of oxygen gas under pressure in a gas cylinder

(b) Liquefaction of air

(c) Keeping petrol in a china dish in the open

(d) Heating copper wire in presence of air at high temperature

Answer:  (d) Heating copper wire in the presence of air at high temperature

[ Heating copper wire in air at high temperature forms copper(II) oxide (2Cu + O₂ → 2CuO), a chemical reaction. Others are physical changes.]

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

(a) 

(b)

(c) 

(d) 

Answer :  (c) 

[  indicates that hydrogen gas (​) and oxygen gas (​) are in the gaseous state before the reaction, and water () is in the liquid state after the reaction.]

18. Which of the following are combination reactions?

(i)

(ii) 

(iii) 

(iv) 

(a) (i) and (iii)      (b) (iii) and (iv)    (c) (ii) and (iv)      (d) (ii) and (iii)

Answer: (d) (ii) and (iii)

[  Combination reactions involve two or more substances combining to form one product.
(ii) MgO + H₂O → Mg(OH)₂ and (iii) 4Al + 3O₂ → 2Al₂O₃ are combination reactions. ]

Short Answer Questions

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  .

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

Answer:  (a) The reaction between nitrogen gas and hydrogen gas to form ammonia gas is a synthesis reaction.

The balanced chemical equation is:

Type of reaction: Combination reaction.

 (b) The reaction between sodium hydroxide (NaOH) solution and acetic acid () to form sodium acetate () and water is a neutralization reaction.

The balanced chemical equation is:

Type of reaction: Neutralisation reaction (double displacement reaction).

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

The balanced chemical equation is: 

Type of reaction: Esterification reaction.

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

The balanced chemical equation is:

Type of reaction: Combustion reaction.

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

 (a) Thermit 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.

Answer: (a) Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s)

Type of reaction: Displacement reaction (Redox / Thermite reaction).

(b) 3Mg(s) + N₂(g) → Mg₃N₂(s)

Type of reaction: Combination reaction.

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

Type of reaction: Displacement reaction (Redox).

(d) C₂H₅OH(l) + 3O₂(g) → 2CO₂(g) + 3H₂O(l) + Heat

Type of reaction: Combustion reaction.

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

(a)  

(b)

(c)

(d)  

Answer: (a)   

(b) 

(c)

(d)

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

Answer: (a) Decomposition of ferrous sulphate: This is an endothermic process because it requires energy to break the bonds within the ferrous sulphate molecule.

(b) Dilution of sulphuric acid: Dilution of an acid is an exothermic process as it releases heat.

(c) Dissolution of sodium hydroxide in water: This is an exothermic process as heat is released when sodium hydroxide dissolves in water.

(d) Dissolution of ammonium chloride in water: This is an endothermic process as it requires energy to break the bonds within the ammonium chloride molecule.

23. Identify the reducing agent in the following reactions

(a)

(b)

(c)

(d)

Answer: (a)

In this reaction, ammonia () is oxidized to form nitrogen monoxide (NO). The reducing agent is ​.

(b)

In this reaction, water () is oxidized to form hydrogen fluoride (HF). The reducing agent is  .

(c) 

In this reaction, carbon monoxide (CO) is oxidized to form carbon dioxide (​). The reducing agent is CO .

(d) 

In this reaction, hydrogen gas (​) is oxidized to form water (). The reducing agent is  .

24. Identify the oxidising agent (oxidant) in the following reactions

(a)

(b)

(c)

(d)

(e)

(f)

Answer:  (a) 

In this reaction, lead(II) oxide () is reduced to form lead(II) chloride (​). The oxidizing agent is  .

(b)     

In this reaction, oxygen () is reduced to form magnesium oxide (MgO). The oxidizing agent is ​.

(c)

In this reaction, zinc (Zn) is oxidized to form zinc sulfate (​). The oxidizing agent is ​.

(d)

In this reaction, calcium (Ca) is oxidized to form calcium oxide (CaO). The oxidizing agent is .

(e) ​

In this reaction, iron (FeFe) is oxidized to form iron(II,III) oxide (​). The oxidizing agent is .

(f)

In this reaction, copper(II) oxide (CuO) is reduced to form copper (Cu). The oxidizing agent is CuO.

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 (), liberates iodine gas and also forms potassium sulphate.

Answer: (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 sulfate on treatment with potassium iodide precipitates cuprous iodide (), liberates iodine gas, and also forms potassium sulphate.

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 the chemical reaction?

Answer: When a solution of potassium chloride (KCl) is mixed with silver nitrate () solution, a white insoluble substance, silver chloride (AgCl), is formed.

The chemical reaction is:

Type of chemical reaction: Double Displacement Reaction or Precipitation Reaction

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.

Answer: The chemical reaction is:

Type of chemical reaction: Thermal Decomposition Reaction .

28. Why do fire flies glow at night?

Answer: Fireflies glow at night due to a chemical reaction inside their bodies. This reaction produces light energy with very little heat, so it is called bioluminescence.

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?

Answer: Grapes ferment after being plucked when yeast acts on the sugar present in them under warm and anaerobic (absence of oxygen) conditions.
Fermentation is a chemical change because new substances like alcohol and carbon dioxide are formed.

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

Answer: (a) Evaporation of petrol → Physical change

(b) Burning of Liquefied Petroleum Gas (LPG) → Chemical change

(c) Heating of an iron rod to red hot → Physical change (though this involves a change in state, it does not involve a change in chemical composition)

(d) Curdling of milk → Chemical change

(e) Sublimation of solid ammonium chloride → Physical change

31. During the reaction of some metals with dilute hydrochloric acid, 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 a gas are seen when lead (Pb) is reacted with the acid.

Explain these observations giving suitable reasons.

Answer:  (a) Silver metal does not show any change:

Silver (Ag) is less reactive than hydrogen, so it does not react with dilute HCl.

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

 Reaction of Al with dilute HCl is exothermic (heat is released).

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

Sodium is highly reactive; it reacts violently/explosively with dilute HCl, producing H₂ gas.

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

Lead reacts slowly with dilute HCl and liberates hydrogen gas (bubbles are observed), though the reaction is slow due to the formation of a protective PbCl₂ layer.

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.

Answer: X is Calcium oxide (CaO), also known as Quicklime.

Element: Calcium (Ca) — Group 2 element, present in bones (as calcium phosphate).

Reactions:  (Calcium hydroxide / Slaked lime)

The solution of Ca(OH)₂ is basic, hence turns red litmus blue.

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.

Answer: (a) (CH₃COO)₂Pb(aq) + 2HCl(aq) → PbCl₂(s) + 2CH₃COOH(aq)

Type of reaction: Double Displacement Reaction (Precipitation Reaction)

(b) 2Na(s) + 2C₂H₅OH(l) → 2C₂H₅ONa(aq) + H₂(g)↑

Type of reaction: Displacement Reaction (Redox)

(c) Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)

Type of reaction: Redox Reaction (Reduction of Fe₂O₃)

(d) 2H₂S(g) + O₂(g) → 2S(s) + 2H₂O(l)

Type of reaction: Redox Reaction (Oxidation)

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

Answer: Silver chloride is stored in dark coloured bottles because it is photosensitive.
When exposed to sunlight, it decomposes into silver (grey) and chlorine gas, turning grey. Dark bottles block light, preventing this decomposition.

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

(a)

(b)

(c)

(d)

(e)

(f)

Answer:  (a)

Type chemical reaction: Combination Reaction

(b)   

Type chemical reaction: Decomposition Reaction (Thermal Decomposition)

(c)

Type chemical reaction: Combination Reaction

(d)

Type chemical reaction: Displacement Reaction

(e)

 Type chemical reaction: Combination Reaction

(f)

Type chemical reaction: Decomposition Reaction (Photochemical Decomposition)

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.

Answer:  (a) X = MgO (Magnesium oxide)

Y = Mg₃N₂ (Magnesium nitride)

(b)  The balance chemical equation is : MgO(s) + H₂O(l) → Mg(OH)₂(aq) (Magnesium hydroxide)

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

Answer:  Zinc (Zn) is placed above hydrogen in the reactivity series, so it can displace hydrogen from dilute HCl.

The chemical reaction: Zn(s) + 2HCl(aq) → ZnCl₂(aq) + H₂(g)

Copper (Cu) is placed below hydrogen in the reactivity series, so it cannot displace hydrogen from dilute acids. Hence, no reaction occurs.

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 give its chemical formula.

Answer:  (a) Silver articles turn black when kept in the open because silver reacts with hydrogen sulphide (H₂S) gas present in the air. Phenomenon: Tarnishing of silver.

(b) Black substance formed: Silver sulphide (Ag₂S)

The chemical reaction: 2Ag(s) + H₂S(g) → Ag₂S(s) + H₂(g) (black)

Long Answer Questions

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) Identity the type of reaction.

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

Answer: (a) Balanced chemical equation of the reaction:

 

(b) The brown gas X evolved is nitrogen dioxide () .

(c) Type of reaction: Thermal decomposition reaction (Decomposition reaction).

(d) Nitrogen dioxide () dissolves in water to form nitric acid () , resulting in an acidic solution. Therefore, the pH range of the aqueous solution of the gas X (nitrogen dioxide) would be acidic.

40. Give the characteristic tests for the following gases

(a)         (b)        (c)           (d)

Answer:  (a) CO₂ (Carbon dioxide) :

Lime water test: Pass the gas through lime water [Ca(OH)₂]. It turns milky due to formation of CaCO₃.

The chemical equation: Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O (Milky appearance disappears on passing excess CO₂ due to soluble Ca(HCO₃)₂)

(b) SO₂ (Sulphur dioxide) :

 Acidified potassium permanganate test: SO₂ decolourises pink/purple KMnO₄ solution.

Acidified potassium dichromate test: SO₂ turns orange K₂Cr₂O₇ solution to green.

(c) O₂ (Oxygen) :

Glowing splint test: A glowing wooden splint rekindles (bursts into flame) when inserted into the gas.

(d) H₂ (Hydrogen):

Pop sound test: Bring a burning splinter near the gas. It burns with a characteristic ‘pop’ sound.

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

Answer:  (a) Zinc metal added to copper sulphate solution :

 

 (b) Aluminium metal  added to dilute hydrochloric acid :

 

(c) ) Silver metal is added to copper sulphate solution :

No reaction occurs because silver is less reactive than copper. Silver does not displace copper from its sulphate solution.

No Reaction:  No Reaction.

42. What happens when zinc granules are treated with dilute solution of  ,,  , and , also write the chemical equations if reaction occurs.

Answer : When zinc granules are treated with different solutions, the then reactions are:

(a) Dilute sulphuric acid (H₂SO₄): Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

(b) Dilute hydrochloric acid (HCl): Zn(s) + 2HCl(aq) →ZnCl₂(aq) + H₂(g)

(c) Dilute nitric acid (HNO₃): Zn(s) + 4HNO₃(aq)→ Zn(NO₃)₂(aq) + 2H₂O(l) + 2NO₂(g)

(d) Sodium chloride (NaCl) solution: No reaction occurs with NaCl because zinc is more reactive than hydrogen but less reactive than sodium. No displacement reaction occurs.

      No Reaction: Zn(s) + 2NaCl(aq) →No Reaction

(e) Sodium hydroxide (NaOH) solution: No reaction occurs with NaOH because zinc is not reactive with hydroxide ions.

     No Reaction: Zn(s) + 2NaOH(aq) →No Reaction

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

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

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

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

Answer : (a) The balanced chemical equation of the reaction is:

(b) This type of precipitation reaction can be called a double displacement reaction .

(c) The white precipitate  is soluble in dilute hydrochloric acid due to the formation of barium chloride and sulphur dioxide gas. The balanced chemical equation for this reaction is:

      

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

Answer: We have,

Container → Solution ↓	Copper container	Aluminium container
Dilute HCl	Yes (no reaction)	No (reacts to form AlCl₃ + H₂)
Dilute HNO₃	Yes (no reaction)	No (reacts, but may passivate? Generally reacts)
ZnCl₂ solution	Yes (no reaction)	No (Al displaces Zn)
H₂O	Yes (no reaction)	Yes (protective oxide layer prevents reaction with pure water at room temperature)