1. Chemical Reactions and Equations

Class 10 Chapter 1: Chemical Reactions and Equations

Chapter 1: 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

(d) Combustion of Liquefied Petroleum Gas (LPG)

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

[ Combustion is a chemical change, not a physical change. In the case of Liquefied Petroleum Gas (LPG) combustion, it produces carbon dioxide, water vapor, and heat, which are different substances compared to the original LPG. Physical changes, on the other hand, involve changes in the physical state or appearance of a substance without the formation of new substances.]

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)

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)

Answer : (c) (i), (ii), and (iv) .

[ The given reaction:

(i) Iron metal is getting oxidized: True.

In the reactants, iron is in the elemental state (Fe), and in the product (), iron is in a higher oxidation state. This indicates oxidation.

(ii) Water is getting reduced: True.

In the reactants, oxygen in water (H₂O) has an oxidation state of -2, and in the product (H₂), it has an oxidation state of 0, indicating reduction.

(iii) Water is acting as a reducing agent: True.

Water is undergoing reduction and, therefore, acts as a reducing agent.

(iv) Water is acting as an oxidizing agent: True.

Since water is undergoing oxidation (losing electrons), it acts as an oxidizing agent.

So, the correct statements are: (c) (i), (ii), and (iv)

This means that iron is oxidized, water is reduced, and water also acts as an oxidizing agent in the given reaction.]

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)

Answer : (a) (i) and (ii).

[ (i) Reaction of water with quicklime: This is an exothermic process because it releases heat when calcium oxide (quicklime) reacts with water to form calcium hydroxide (slaked lime).

(ii) Dilution of an acid: Diluting an acid is an exothermic process. When an acid is mixed with water, it releases heat to the surroundings.

(iii) Evaporation of water: This is an endothermic process. It requires heat from the surroundings to convert liquid water into vapor.

(iv) Sublimation of camphor (crystals): Sublimation is typically an endothermic process, meaning it absorbs heat from the surroundings. When camphor crystals undergo sublimation, they directly change from a solid to a vapor phase.

So, the only exothermic processes among the given options are (i) and (ii). ]

5. Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous 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

Answer : (c) (i) and (iv)

[ In beaker A, NaOH is added to water, and the dissolution of NaOH in water is an exothermic process. It releases heat to the surroundings, causing the temperature to increase.

In beaker B, anhydrous is added to water, and the dissolution of anhydrous in water is also an exothermic process. It releases heat to the surroundings, leading to a temperature increase.

In beaker C, NaCl is added to water, and the dissolution of NaCl in water is an endothermic process. It absorbs heat from the surroundings, causing the temperature to decrease.

Therefore, statements (i) and (iv) are correct, indicating that exothermic processes occurred in beakers A and B, while an endothermic process occurred in beaker C.]

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

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

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

[ Potassium permanganate () is a strong oxidizing agent.

Ferrous sulfate () is a reducing agent.

When ferrous sulfate is added to acidified potassium permanganate solution, the manganese in undergoes reduction, resulting in the formation of colorless manganese ions.

The purple color of the permanganate solution fades and finally disappears because the manganese ions formed are colorless.

Therefore, 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

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.

In option (ii), 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)

Answer : (a) (i) only

[ Exposure of silver chloride (AgCl) to sunlight for a long duration causes it to turn grey due to the decomposition of silver chloride.

Sunlight provides energy to break the chemical bonds in silver chloride, leading to the release of silver and chlorine gas.

The decomposition reaction is represented as:

Therefore, statement (i) is true.

Statement (ii) is incorrect because sublimation involves the direct transition from a solid to a gas, and in this case, it's a decomposition reaction.

Statement (iii) is incorrect because the released product is chlorine gas, not the decomposition of chlorine gas from silver chloride.

Statement (iv) is incorrect because silver chloride turning grey is not due to oxidation; it's primarily a result of decomposition.

So, the correct answer is (a) (i) only. ]

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)

Answer : (b) (ii) and (iii)

[ The slaking of lime is an exothermic reaction because it releases heat when solid calcium oxide reacts with water to form calcium hydroxide.

The resulting solution, lime water dissolved in water), is basic. When calcium hydroxide dissolves in water, it forms hydroxide ions() , making the solution alkaline. Therefore, the pH of the resulting solution will be more than seven.

So, the correct answer is (b) (ii) and (iii). ]

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

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

[ In the given reaction :

This is a double displacement reaction (iv) because the positive and negative ions from two different compounds exchange places to form two new compounds.

Additionally, it is also a precipitation reaction (ii) because the formation of barium sulfate results in the precipitation of a solid (barium sulphate) from the solution.

So, the correct answer is (d) (ii) and (iv). ]

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

(d) 1:2

Answer : (b) 2:1.

[

For every two moles of water molecules, one mole of oxygen gas and two moles of hydrogen gas are produced. Therefore, the mole ratio of hydrogen to oxygen is 2:1. ]

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

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

[ Sublimation of dry ice () involves the transition from a solid to a gas, which typically requires an input of energy.

Evaporation of water involves the phase transition from a liquid to a gas, and this process absorbs heat.

Therefore, the correct answer is (d) (ii) and (iv).]

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

(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

(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

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

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

[

This is a decomposition reaction as a single substance () breaks down into multiple products (KCl and ).

The addition of heat (endothermic) is required for this reaction to proceed.

Therefore, the correct answer is (a) It is a decomposition reaction and endothermic in nature.]

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

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

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

[ When copper wire is heated in the presence of air at high temperatures, it undergoes oxidation, forming copper oxide. This is a chemical reaction.

The other options describe physical processes:

(a) Storing of oxygen gas under pressure in a gas cylinder is a physical process.

(b) Liquefaction of air is a physical process.

Therefore, the correct answer is (d) Heating copper wire in the presence of air at high temperature.]

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)

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

[ Combination reactions involve the formation of a single product from two or more reactants. The given reactions are :

(i)

This is a decomposition reaction, not a combination reaction.

(ii)

This is a neutralization reaction, not a combination reaction.

(iii)

This is a combination reaction as aluminum reacts with oxygen to form aluminum oxide .

(iv)

This is a displacement reaction, not a combination reaction.

So, the correct answer is: (d) (ii) and (iii) ]

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.

(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:

(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:

Balanced Chemical Equation:

Type of Reaction: Esterification: An organic reaction in which a carboxylic acid reacts with an alcohol to form an ester and water.

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

Balanced Chemical Equation:

Type of Reaction: Combustion: A reaction where a hydrocarbon reacts with oxygen to produce carbon dioxide, water, and energy (heat and light).

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.

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

Answer : (a) Displacement or Redox Reaction :

Type of Reaction: Displacement or Redox Reaction

(b) Combination Reaction:

Type of Reaction: Combination Reaction.

Type of Reaction: Displacement or Redox Reaction

(d) Combustion Reaction:

Type of Reaction: Combustion Reaction

In combustion reactions, heat is released as a product.

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 exother mic or endothermic in nature?

(a) Decomposition of ferrous sulphate

(b) Dilution of sulphuric acid

(d) Dissolution of ammonium chloride in water

Solution : (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.

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 : The reducing agent in a chemical reaction is the substance that undergoes oxidation and, in the process, provides electrons to another substance. The given reactions are:

(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 : The oxidizing agent (oxidant) in a chemical reaction is the substance that undergoes reduction and, in the process, accepts electrons from another substance. The oxidizing agent in each of the given reactions:

(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 (Fe) 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

In this reaction, the ions from the reactants exchange partners, leading to the formation of an insoluble solid (precipitate), which is silver chloride in this case.

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 decomposition of ferrous sulphate () with the evolution of a gas having a characteristic odor of burning sulfur can be represented by the following chemical reaction:

Type of Reaction: Decomposition Reaction

In this reaction, ferrous sulfate decomposes into ferric oxide (), sulphur dioxide (), and oxygen (). The evolution of sulphur dioxide is responsible for the characteristic odor of burning sulphur.

28. Why do fire flies glow at night?

Answer : Fireflies glow at night due to a process called bioluminescence. They produce light through a chemical reaction involving luciferin and luciferase enzymes in their abdomen. This light emission serves various purposes, including attracting mates and deterring predators.

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 : The fermentation of grapes occurs when they are plucked from the plant and exposed to specific conditions, typically involving the presence of yeast. This process is a chemical change, as it involves the conversion of sugars in the grapes into alcohol and carbon dioxide through the action of microorganisms like yeast.

30. Which among the following are physical or chemical changes?

(a) Evaporation of petrol

(b) Burning of Liquefied Petroleum Gas (LPG)

(d) Curdling of milk

(e) Sublimation of solid ammonium chloride

Answer : The nature of changes in the given options:

(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.

(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 (Ag) : Silver does not react with dilute hydrochloric acid because it is a less reactive metal. It does not easily release hydrogen ions to form silver chloride.

(b) Amuminium (Al) :The temperature of the reaction mixture rises when aluminium is added because aluminium reacts with hydrochloric acid to produce aluminium chloride and hydrogen gas. The reaction is exothermic, releasing heat.

(c) Sodium (Na) : The reaction of sodium with hydrochloric acid is highly explosive. Sodium is a very reactive metal, and the reaction is vigorous, producing sodium chloride and hydrogen gas.

(d) Lead (Pb) : Bubbles of gas are seen when lead reacts with hydrochloric acid. The reaction produces lead chloride and hydrogen gas.

However, lead does not react as vigorously as sodium, and the reaction is relatively slower compared to more reactive metals

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 : The substance X, which is an oxide of a Group 2 element and is used in the cement industry and is present in bones, is likely calcium oxide () .

The chemical reaction involved in the reaction with water is the formation of calcium hydroxide () , which turns red litmus blue, indicating its basic (alkaline) nature.

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.

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

Answer : (a)

Classification: Double Displacement Reaction or Precipitation Reaction

(b)

Classification: Displacement Reaction

(c)

Classification: Reduction (Redox) Reaction

(d) Hydrogen sulphide gas with oxygen gas:

Classification: Combination Reaction.

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

Answer : Silver chloride is sensitive to light and can decompose into silver and chlorine in the presence of light. Storing it in dark-colored bottles protects it from light exposure, preventing unwanted reactions and preserving its stability.

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

(a)

(b)

(c)

(d)

(e)

(f)

Answer : (a)

Type: Combination Reaction

(b)

Type: Decomposition Reaction (Thermal Decomposition)

(c)

Type: Combination Reaction

(d)

Type: Displacement Reaction

(e)

Type: Combination Reaction

(f)

Type: 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) The white compound formed when magnesium ribbon is burnt in oxygen is magnesium oxide ()(X). The compound formed when the burning ribbon is placed in an atmosphere of nitrogen is magnesium nitride () (Y).

(b) Balanced chemical equation when magnesium oxide () is dissolved in water:

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

Answer : The reactivity of metals with acids depends on their position in the reactivity series. Zinc is higher in the reactivity series than hydrogen, while copper is lower.

Zinc can displace hydrogen from hydrochloric acid, leading to the liberation of hydrogen gas. On the other hand, copper is less reactive, and it does not displace hydrogen from acids. The reactivity series helps predict whether a metal will react with an acid to liberate hydrogen.

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 exposed to air due to the formation of silver sulphide() , a compound formed by the reaction of silver with hydrogen sulphide ( gas) present in the atmosphere. The phenomenon is known as tarnishing.

(b) The black substance formed is silver sulphide ( ), and its chemical formula is( ) .

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.

(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 () .

(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) (Carbon Dioxide): Bubble the gas through limewater (calcium hydroxide solution). If is present, the limewater turns milky due to the formation of calcium carbonate.

The reaction is:

(b) The characteristic test for sulphur dioxide (SO₂) gas includes its pungent, irritating smell, similar to that of burning sulfur or rotten eggs. It also decolorizes acidified potassium permanganate solution from purple to colorless.

(c) (Oxygen): Insert a glowing splint into the gas. If oxygen is present, the splint will reignite or glow more brightly due to the increased availability of oxygen, which supports combustion.

(d) (Hydrogen): Bring a lit splint close to the gas. Hydrogen burns with a characteristic "pop" sound, indicating its presence. This is due to the rapid exothermic reaction between hydrogen and oxygen forming water:

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?

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 :

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)

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?

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 : Copper is relatively inert to dilute HCl and dilute HNO₃. Therefore, both the solutions can be kept in the container made of copper.

However, aluminum reacts with both dilute HCl and dilute HNO₃, forming aluminum chloride () and aluminum nitrate (), respectively. Therefore, these solutions should not be kept in the container made of aluminum.

ZnCl₂ (zinc chloride) is not reactive with copper or aluminum, so it can be kept in containers made of either metal.

Water (H₂O) is not reactive with copper or aluminum, so it can also be kept in containers made of either metal.