Comprehensive Question Bank with Answers

Kerala SCERT • English Medium • 

(Includes multiple-choice questions, statement-based questions, assertion–reason, fill in the blanks, true/false, match the following, chemical equations, short answers, application-based questions and revision notes.)

Section 1: Multiple-Choice Questions (MCQs)

Choose the correct answer. The correct option and a brief explanation are provided.

A. Basic concepts and definitions

1. Electrochemistry is the branch of chemistry that studies:
2. Only the properties of metals
3. The production of electricity from chemical reactions and chemical changes caused by electricity
4. Only acids and bases
5. Only the preparation of salts

Answer: B. The production of electricity from chemical reactions and chemical changes caused by electricity Electrochemistry deals with the relationship between chemical reactions and electrical energy.

2. A device that produces electricity from chemical reactions is called a:
3. Transformer
4. Electrolytic cell
5. Galvanic cell
6. Heating element

Answer: C. Galvanic cell A galvanic cell converts chemical energy into electrical energy.

3. Which of the following is an example of a galvanic cell?
4. Daniell cell
5. Electroplating cell
6. Electrolysis of water
7. Electrolysis of molten NaCl

Answer: A. Daniell cell A Daniell cell produces electricity through a redox reaction.

4. Which cell uses electrical energy to bring about chemical changes?
5. Galvanic cell
6. Electrolytic cell
7. Daniell cell only
8. Fuel cell only

Answer: B. Electrolytic cell An electrolytic cell uses an external electrical source to drive a chemical reaction.

5. A Daniell cell contains:
6. Zinc and iron electrodes
7. Copper and silver electrodes
8. Zinc and copper electrodes
9. Magnesium and aluminium electrodes

Answer: C. Zinc and copper electrodes The Daniell cell uses zinc and copper electrodes.

6. The electrolyte around the zinc electrode in a Daniell cell is:
7. CuSO₄ solution
8. ZnSO₄ solution
9. AgNO₃ solution
10. NaCl solution

Answer: B. ZnSO₄ solution The zinc half-cell contains zinc sulphate solution.

7. The electrolyte around the copper electrode in a Daniell cell is:
8. ZnSO₄ solution
9. MgSO₄ solution
10. CuSO₄ solution
11. AgNO₃ solution

Answer: C. CuSO₄ solution The copper half-cell contains copper sulphate solution.

8. The two half-cells of a Daniell cell are connected by a:
9. Fuse
10. Salt bridge
11. Plastic rod
12. Rubber tube without electrolyte

Answer: B. Salt bridge The salt bridge allows ion movement and maintains electrical neutrality.

9. Which instrument detects the flow of electric current in a Daniell cell?
10. Thermometer
11. Barometer
12. Galvanometer
13. Hydrometer

Answer: C. Galvanometer A galvanometer detects small electric currents.

10. The standard cell voltage of a Daniell cell is approximately:
11. 0.46 V
12. 1.10 V
13. 2.70 V
14. 0 V

Answer: B. 1.10 V The standard voltage of a Zn–Cu Daniell cell is about 1.10 V.

11. The electrode at which oxidation occurs is called the:
12. Cathode
13. Anode
14. Electrolyte
15. Salt bridge

Answer: B. Anode Oxidation always takes place at the anode.

12. The electrode at which reduction occurs is called the:
13. Anode
14. Cathode
15. Salt bridge
16. Voltmeter

Answer: B. Cathode Reduction always takes place at the cathode.

13. In a Daniell cell, the anode is the:
14. Copper electrode
15. Zinc electrode
16. Salt bridge
17. Voltmeter

Answer: B. Zinc electrode Zinc loses electrons and is oxidised at the anode.

14. In a Daniell cell, the cathode is the:
15. Zinc electrode
16. Copper electrode
17. Salt bridge
18. Connecting wire

Answer: B. Copper electrode Copper ions gain electrons at the copper cathode.

15. In a Daniell cell, electrons flow through the external wire:
16. From Cu to Zn
17. From Zn to Cu
18. From salt bridge to Zn
19. From CuSO₄ to ZnSO₄

Answer: B. From Zn to Cu Electrons are released at zinc and travel through the external circuit to copper.

16. Conventional electric current in the external circuit of a Daniell cell flows:
17. From Zn to Cu
18. From Cu to Zn
19. Only through the salt bridge
20. From electrolyte to zinc rod

Answer: B. From Cu to Zn Conventional current is opposite to electron flow.

17. The salt bridge in a galvanic cell mainly helps to:
18. Stop all ion movement
19. Maintain electrical neutrality in the half-cells
20. Produce zinc metal
21. Increase electrode mass

Answer: B. Maintain electrical neutrality in the half-cells Ion movement through the salt bridge completes the internal circuit.

18. Which process takes place at the zinc electrode in a Daniell cell?
19. Reduction
20. Oxidation
21. Neutralisation
22. Electroplating

Answer: B. Oxidation Zn(s) → Zn²⁺(aq) + 2e⁻.

19. Which process takes place at the copper electrode in a Daniell cell?
20. Oxidation of copper ions
21. Reduction of copper ions
22. Oxidation of zinc ions
23. Combustion

Answer: B. Reduction of copper ions Cu²⁺(aq) + 2e⁻ → Cu(s).

20. The overall reaction in a Daniell cell is:
21. Zn + Cu²⁺ → Zn²⁺ + Cu
22. Cu + Zn²⁺ → Cu²⁺ + Zn
23. Zn²⁺ + Cu²⁺ → Zn + Cu
24. Zn + Cu → Zn²⁺ + Cu²⁺

Answer: A. Zn + Cu²⁺ → Zn²⁺ + Cu Zinc is oxidised while copper ions are reduced.

B. Redox reactions and reactivity series

21. In Mg + CuSO₄ → MgSO₄ + Cu, which metal is oxidised?
22. Copper
23. Magnesium
24. Both metals
25. Neither metal

Answer: B. Magnesium Mg → Mg²⁺ + 2e⁻. Magnesium loses electrons.

22. In Mg + Cu²⁺ → Mg²⁺ + Cu, which ion is reduced?
23. Mg²⁺
24. Cu²⁺
25. SO₄²⁻
26. OH⁻

Answer: B. Cu²⁺ Cu²⁺ gains two electrons to form copper metal.

23. A substance that causes oxidation is called the:
24. Reducing agent
25. Oxidising agent
26. Electrolyte
27. Catalyst only

Answer: B. Oxidising agent The oxidising agent causes oxidation and itself undergoes reduction.

24. A substance that causes reduction is called the:
25. Oxidising agent
26. Reducing agent
27. Anode
28. Cathode

Answer: B. Reducing agent The reducing agent causes reduction and itself undergoes oxidation.

25. In a redox reaction, the oxidising agent undergoes:
26. Oxidation
27. Reduction
28. No change in any case
29. Electroplating

Answer: B. Reduction The oxidising agent accepts electrons and is reduced.

26. In a redox reaction, the reducing agent undergoes:
27. Reduction
28. Oxidation
29. Only melting
30. Only evaporation

Answer: B. Oxidation The reducing agent donates electrons and is oxidised.

27. When copper is placed in silver nitrate solution, which metal is deposited?
28. Zinc
29. Magnesium
30. Silver
31. Iron

Answer: C. Silver Copper displaces silver from silver nitrate solution.

28. Why can silver nitrate solution not be stored in a copper vessel?
29. Copper is less reactive than silver
30. Copper displaces silver from the solution
31. Silver nitrate is always a gas
32. Copper does not conduct electricity

Answer: B. Copper displaces silver from the solution Copper reacts with silver nitrate, depositing silver and forming copper ions.

29. In Cu + 2AgNO₃ → Cu(NO₃)₂ + 2Ag, the reducing agent is:
30. Ag
31. Ag⁺
32. Cu
33. NO₃⁻

Answer: C. Cu Copper loses electrons and reduces silver ions.

30. In Cu + 2Ag⁺ → Cu²⁺ + 2Ag, the oxidising agent is:
31. Cu
32. Cu²⁺
33. Ag⁺
34. Ag

Answer: C. Ag⁺ Silver ions accept electrons and are reduced.

31. Which metal reacts most vigorously with dilute HCl among Mg, Zn, Fe, Pb and Cu?
32. Cu
33. Pb
34. Fe
35. Mg

Answer: D. Mg Magnesium is the most reactive among the listed metals.

32. Which metal does not liberate hydrogen from dilute HCl under ordinary conditions?
33. Magnesium
34. Zinc
35. Iron
36. Copper

Answer: D. Copper Copper is below hydrogen in the usual school-level reactivity series.

33. Which pair contains metals that can displace hydrogen from dilute HCl?
34. Gold and silver
35. Copper and gold
36. Sodium and aluminium
37. Silver and copper

Answer: C. Sodium and aluminium Sodium and aluminium are above hydrogen in the reactivity series. Sodium reacts extremely vigorously with water and must not be tested casually with acid.

34. As metal reactivity decreases, the rate of hydrogen liberation from dilute acid generally:
35. Increases
36. Decreases
37. Always remains the same
38. Becomes zero for all metals

Answer: B. Decreases More reactive metals generally react faster with dilute acids.

35. In a galvanic cell, the more reactive metal generally acts as the:
36. Cathode
37. Anode
38. Salt bridge
39. Electrolyte

Answer: B. Anode The more reactive metal tends to lose electrons and undergo oxidation.

C. Electrolysis and electroplating

36. Electrolysis is the process in which:
37. Chemical energy becomes sound
38. An electrolyte undergoes chemical changes when electricity passes through it
39. A metal reacts only with oxygen
40. A salt bridge produces electrons

Answer: B. An electrolyte undergoes chemical changes when electricity passes through it Electrolysis uses electrical energy to drive chemical changes.

37. Which solution can conduct electricity in aqueous solution?
38. Sugar solution
39. Sodium chloride solution
40. Pure kerosene
41. Paraffin wax

Answer: B. Sodium chloride solution Sodium chloride solution contains mobile ions.

38. Why does solid sodium chloride not conduct electricity effectively?
39. It has no ions
40. Its ions are not free to move
41. It contains only electrons
42. It is a metal

Answer: B. Its ions are not free to move In solid NaCl, ions are held in fixed positions in the crystal lattice.

39. During electrolysis of molten sodium chloride, sodium is formed at the:
40. Anode
41. Cathode
42. Salt bridge
43. Both electrodes equally

Answer: B. Cathode Na⁺ ions gain electrons at the cathode.

40. During electrolysis of molten sodium chloride, chlorine gas is formed at the:
41. Cathode
42. Anode
43. Battery terminal only
44. Salt bridge

Answer: B. Anode Chloride ions lose electrons at the anode.

41. During electrolysis of acidified water, the gas at the cathode is:
42. Oxygen
43. Hydrogen
44. Chlorine
45. Nitrogen

Answer: B. Hydrogen Hydrogen is produced at the cathode.

42. During electrolysis of acidified water, the gas at the anode is:
43. Hydrogen
44. Oxygen
45. Carbon dioxide
46. Ammonia

Answer: B. Oxygen Oxygen is produced at the anode.

43. The approximate volume ratio of hydrogen to oxygen from electrolysis of water is:
44. 1:1
45. 1:2
46. 2:1
47. 3:1

Answer: C. 2:1 2H₂O → 2H₂ + O₂, so the gas volume ratio is 2:1.

44. Which gas burns with a pop sound when tested with a flame?
45. Oxygen
46. Hydrogen
47. Nitrogen
48. Carbon dioxide

Answer: B. Hydrogen The pop test is a common school-level test for hydrogen.

45. In electrolysis of aqueous sodium chloride, which gas forms at the cathode?
46. Chlorine
47. Oxygen
48. Hydrogen
49. Nitrogen

Answer: C. Hydrogen Water is reduced at the cathode, producing hydrogen and hydroxide ions.

46. In electrolysis of aqueous sodium chloride, which gas forms at the anode in the textbook setup?
47. Hydrogen
48. Chlorine
49. Nitrogen
50. Carbon monoxide

Answer: B. Chlorine Chloride ions are oxidised to chlorine gas at the anode.

47. The solution around the cathode becomes basic because of formation of:
48. H⁺ ions
49. OH⁻ ions
50. Ag⁺ ions
51. Cu²⁺ ions

Answer: B. OH⁻ ions Water reduction produces OH⁻ ions along with hydrogen.

48. In electroplating, the object to be coated is connected to the:
49. Positive terminal as anode
50. Negative terminal as cathode
51. Salt bridge
52. Voltmeter only

Answer: B. Negative terminal as cathode Metal ions gain electrons on the object, depositing the coating.

49. In copper electroplating of an iron ring, the copper plate is connected to the:
50. Negative terminal
51. Positive terminal
52. Salt bridge only
53. No terminal

Answer: B. Positive terminal The copper plate is the anode and dissolves to replenish Cu²⁺ ions.

50. In copper electroplating, the iron ring is the:
51. Anode
52. Cathode
53. Electrolyte
54. Salt bridge

Answer: B. Cathode Cu²⁺ ions are reduced on the iron ring, depositing copper.

51. Which electrolyte is used for copper plating of an iron ring in the textbook experiment?
52. Silver nitrate
53. Copper sulphate
54. Zinc sulphate
55. Sodium hydroxide only

Answer: B. Copper sulphate CuSO₄ solution supplies copper ions for the coating.

52. Electroplating is used to:
53. Coat one metal with another metal
54. Turn all metals into gases
55. Stop all chemical reactions
56. Produce only hydrogen

Answer: A. Coat one metal with another metal Electroplating deposits a thin layer of one metal on another object.

53. Which is a common application of electrolysis?
54. Purification of certain metals
55. Producing gravity
56. Preventing all oxidation
57. Making metals non-conductive

Answer: A. Purification of certain metals Electrolysis is used in metal production, purification, electroplating and chemical manufacture.

D. Cells, batteries and fuel cells

54. A primary cell:
55. Can always be recharged
56. Cannot normally be recharged after its reactants are used up
57. Works only with a salt bridge
58. Always contains a lithium-ion electrolyte

Answer: B. Cannot normally be recharged after its reactants are used up Primary cells are generally non-rechargeable.

55. Which is an example of a secondary cell?
56. Ordinary dry cell
57. Button cell
58. Lead-acid accumulator
59. All primary cells

Answer: C. Lead-acid accumulator A lead-acid accumulator can be recharged.

56. A lithium-ion battery is generally classified as a:
57. Primary cell
58. Secondary cell
59. Salt bridge
60. Fuel cell only

Answer: B. Secondary cell Lithium-ion batteries are rechargeable secondary cells.

57. Which is a primary cell example mentioned in the chapter?
58. Lead-acid accumulator
59. Lithium-ion battery
60. Dry cell
61. Rechargeable nickel-cadmium cell

Answer: C. Dry cell Dry cells are listed as primary cells in the textbook.

58. Fuel cells convert the chemical energy of fuels into:
59. Electrical energy
60. Only heat energy
61. Only sound energy
62. Mechanical energy without electricity

Answer: A. Electrical energy Fuel cells convert fuel-related chemical energy into electricity.

59. Which of the following may be used as a fuel in fuel-cell systems?
60. Hydrogen
61. Sand
62. Copper metal only
63. Sodium chloride crystals

Answer: A. Hydrogen Hydrogen is one of the fuels discussed in the chapter.

60. One advantage of fuel cells mentioned in the chapter is:
61. They never need reactants
62. They can produce electricity with high efficiency
63. They work without chemical reactions
64. They cannot produce electricity

Answer: B. They can produce electricity with high efficiency Fuel cells can convert chemical energy into electrical energy efficiently.

61. Which is an application of secondary cells?
62. Rechargeable batteries in vehicles
63. Salt bridges only
64. Only non-rechargeable dry cells
65. Non-conducting electrolytes

Answer: A. Rechargeable batteries in vehicles Rechargeable batteries are used in vehicles and electronic devices.

Section 2: Statement-Based Questions

For each question, select all the correct statements.

1. Consider the statements about a Daniell cell.

• a) Zinc is the anode.
• b) Copper is the cathode.
• c) Oxidation occurs at the copper electrode.
• d) Electrons flow from zinc to copper through the external wire.

Correct: a, b and d. Oxidation occurs at zinc, not copper.

2. Consider the statements about galvanic cells.

• a) They convert chemical energy into electrical energy.
• b) They produce electricity through redox reactions.
• c) Oxidation occurs at the anode.
• d) Reduction occurs at the anode.

Correct: a, b and c. Reduction occurs at the cathode.

3. Consider the statements about electrolytic cells.

• a) They use electrical energy to bring about chemical changes.
• b) Oxidation occurs at the anode.
• c) Reduction occurs at the cathode.
• d) The anode is always negative.

Correct: a, b and c. In an electrolytic cell, the anode is positive and the cathode is negative.

4. Consider the statements about a salt bridge.

• a) It connects the two half-cells.
• b) It allows ions to move between the half-cells.
• c) It helps maintain electrical neutrality.
• d) It supplies electrons through the external circuit.

Correct: a, b and c. Electrons travel through the external wire, not the salt bridge.

5. Consider the statements about oxidation and reduction.

• a) Oxidation involves loss of electrons.
• b) Reduction involves gain of electrons.
• c) The oxidising agent undergoes reduction.
• d) The reducing agent undergoes reduction.

Correct: a, b and c. The reducing agent undergoes oxidation.

6. Consider the statements about electrolysis of acidified water.

• a) Hydrogen is liberated at the cathode.
• b) Oxygen is liberated at the anode.
• c) Hydrogen is produced in approximately twice the volume of oxygen.
• d) Oxygen burns with a pop sound.

Correct: a, b and c. Hydrogen gives the characteristic pop test. Oxygen supports combustion.

7. Consider the statements about electroplating.

• a) The object to be coated is connected to the negative terminal.
• b) The plating metal is generally connected to the positive terminal in the textbook setup.
• c) The electrolyte contains ions of the coating metal.
• d) Metal is deposited on the anode as the coating.

Correct: a, b and c. The coating metal is deposited on the cathode.

8. Consider the statements about aqueous sodium chloride electrolysis.

• a) Hydrogen is produced at the cathode.
• b) Chlorine is produced at the anode in the textbook setup.
• c) OH⁻ ions form near the cathode.
• d) Sodium metal is deposited at the cathode in this aqueous setup.

Correct: a, b and c. In aqueous NaCl, water is reduced at the cathode; sodium metal is not deposited.

9. Consider the statements about reactivity and displacement.

• a) A more reactive metal can displace a less reactive metal from its salt solution.
• b) Copper displaces silver from silver nitrate solution.
• c) Silver displaces copper from copper sulphate solution under ordinary conditions.
• d) More reactive metals generally lose electrons more readily.

Correct: a, b and d. Silver is less reactive than copper and cannot displace copper from CuSO₄.

10. Consider the statements about cells and batteries.

• a) A primary cell is generally not rechargeable.
• b) A secondary cell can be recharged.
• c) A lithium-ion battery is a secondary cell.
• d) A fuel cell converts chemical energy into electrical energy.

Correct: a, b, c and d. All four statements are correct.

Section 3: Assertion–Reason Questions

Choose: A) Both true and Reason correctly explains Assertion. B) Both true but Reason does not correctly explain Assertion. C) Assertion true, Reason false. D) Assertion false, Reason true.

1. Assertion: Zinc acts as the anode in a Daniell cell.

Reason: Oxidation takes place at the anode.

Answer: A. Both are true, and oxidation explains why zinc is the anode.

2. Assertion: Copper acts as the cathode in a Daniell cell.

Reason: Reduction of Cu²⁺ ions occurs at the copper electrode.

Answer: A. Copper ions gain electrons at the cathode and deposit as copper metal.

3. Assertion: Electrons flow from copper to zinc in a Daniell cell.

Reason: Zinc loses electrons during the cell reaction.

Answer: D. Electrons flow from zinc to copper. The reason is true.

4. Assertion: The salt bridge helps maintain electrical neutrality in a galvanic cell.

Reason: Ions can move through the salt bridge.

Answer: A. Ion movement through the salt bridge helps prevent charge build-up.

5. Assertion: An oxidising agent undergoes reduction.

Reason: An oxidising agent accepts electrons.

Answer: A. Accepting electrons is reduction.

6. Assertion: A reducing agent undergoes oxidation.

Reason: A reducing agent loses electrons.

Answer: A. Loss of electrons is oxidation.

7. Assertion: Copper is deposited on an iron ring during copper electroplating.

Reason: The iron ring acts as the cathode.

Answer: A. Cu²⁺ ions gain electrons at the cathode and deposit on the ring.

8. Assertion: Hydrogen is collected at the anode during electrolysis of acidified water.

Reason: Hydrogen ions gain electrons at the cathode.

Answer: D. Hydrogen is collected at the cathode; the reason is true.

9. Assertion: Copper cannot normally displace zinc from zinc sulphate solution.

Reason: Zinc is more reactive than copper.

Answer: A. Copper is less reactive and cannot displace zinc from its salt solution.

10. Assertion: A lead-acid accumulator is a secondary cell.

Reason: A secondary cell can be recharged.

Answer: B. Both statements are true; the reason is a general property, not a direct explanation of the specific classification.

11. Assertion: During electrolysis of aqueous sodium chloride, the solution near the cathode can become basic.

Reason: Hydroxide ions are formed near the cathode.

Answer: A. Water reduction forms hydrogen and OH⁻ ions.

12. Assertion: The anode is always positive in every type of electrochemical cell.

Reason: Oxidation always occurs at the anode.

Answer: D. The anode is positive in an electrolytic cell but negative in a galvanic cell. Oxidation always occurs at the anode.

Section 4: Fill in the Blanks

1. The branch of chemistry that studies the relationship between chemical reactions and electricity is called ______. Answer: Electrochemistry
2. A cell that converts chemical energy into electrical energy is called a ______. Answer: Galvanic cell
3. A cell that uses electrical energy to bring about chemical changes is called an ______. Answer: Electrolytic cell
4. In a Daniell cell, the zinc electrode is the ______. Answer: Anode
5. In a Daniell cell, the copper electrode is the ______. Answer: Cathode
6. Oxidation occurs at the ______. Answer: Anode
7. Reduction occurs at the ______. Answer: Cathode
8. The electrolyte in the zinc half-cell is ______ solution. Answer: Zinc sulphate
9. The electrolyte in the copper half-cell is ______ solution. Answer: Copper sulphate
10. The two half-cells of a Daniell cell are connected using a ______. Answer: Salt bridge
11. In a Daniell cell, electrons flow from ______ to ______. Answer: Zinc to copper
12. The standard voltage of a Daniell cell is approximately ______. Answer: 1.10 V
13. Loss of electrons is called ______. Answer: Oxidation
14. Gain of electrons is called ______. Answer: Reduction
15. A substance that causes oxidation is called an ______. Answer: Oxidising agent
16. A substance that causes reduction is called a ______. Answer: Reducing agent
17. During electrolysis of acidified water, ______ is liberated at the cathode. Answer: Hydrogen
18. During electrolysis of acidified water, ______ is liberated at the anode. Answer: Oxygen
19. The volume ratio of hydrogen to oxygen in water electrolysis is ______. Answer: 2:1
20. During electrolysis of molten sodium chloride, ______ is formed at the cathode. Answer: Sodium metal
21. During electrolysis of molten sodium chloride, ______ gas is liberated at the anode. Answer: Chlorine
22. In electroplating, the object to be coated is connected to the ______ terminal. Answer: Negative
23. In the textbook electroplating setup, the plating metal is connected to the ______ terminal. Answer: Positive
24. The process of coating an object with a metal by electrolysis is called ______. Answer: Electroplating
25. A rechargeable cell is called a ______ cell. Answer: Secondary

Section 5: True or False

Section 6: Match the Following

Question 1: Electrochemical cells

Answer: 1–C, 2–A, 3–E, 4–D, 5–B.

Question 2: Electrolysis

Answer: 1–B, 2–C, 3–A, 4–D, 5–E.

Question 3: Batteries and applications

Answer: 1–C, 2–A, 3–B, 4–D, 5–E.

Section 7: Important Chemical Equations

1. Oxidation at zinc electrode: Zn(s) → Zn²⁺(aq) + 2e⁻
2. Reduction at copper electrode: Cu²⁺(aq) + 2e⁻ → Cu(s)
3. Overall Daniell cell reaction: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)
4. Oxidation of magnesium: Mg(s) → Mg²⁺(aq) + 2e⁻
5. Reduction of copper ions: Cu²⁺(aq) + 2e⁻ → Cu(s)
6. Copper displacing silver: Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s)
7. Oxidation of copper in silver nitrate reaction: Cu(s) → Cu²⁺(aq) + 2e⁻
8. Reduction of silver ions: 2Ag⁺(aq) + 2e⁻ → 2Ag(s)
9. Overall electrolysis of water: 2H₂O(l) → 2H₂(g) + O₂(g)
10. Reduction of sodium ions: Na⁺ + e⁻ → Na
11. Oxidation of chloride ions: 2Cl⁻ → Cl₂(g) + 2e⁻
12. Reduction of water in aqueous NaCl: 2H₂O + 2e⁻ → H₂(g) + 2OH⁻
13. Oxidation during copper electroplating: Cu(s) → Cu²⁺(aq) + 2e⁻
14. Reduction during copper electroplating: Cu²⁺(aq) + 2e⁻ → Cu(s)

Section 8: Short-Answer Questions

1. What is electrochemistry?

Answer: Electrochemistry is the branch of chemistry that studies the production of electricity through chemical reactions and the chemical changes brought about by electricity.

2. What is an electrochemical cell?

Answer: An electrochemical cell is a device in which chemical and electrical energy are interconverted through electrochemical reactions.

3. What is a galvanic cell?

Answer: A galvanic cell converts chemical energy into electrical energy through a spontaneous redox reaction.

4. What is an electrolytic cell?

Answer: An electrolytic cell uses electrical energy to bring about a chemical change that would not occur spontaneously under the given conditions.

5. What is a Daniell cell?

Answer: A Daniell cell is a galvanic cell consisting of a zinc electrode in zinc sulphate solution and a copper electrode in copper sulphate solution, connected by a salt bridge and an external wire.

6. What are the functions of a salt bridge?

Answer: It completes the internal circuit by permitting ion movement, maintains electrical neutrality in the half-cells, and prevents excessive charge accumulation.

7. What happens at the zinc electrode of a Daniell cell?

Answer: Zinc atoms lose two electrons and enter the solution as zinc ions. Oxidation occurs: Zn(s) → Zn²⁺(aq) + 2e⁻.

8. What happens at the copper electrode of a Daniell cell?

Answer: Copper ions gain electrons and deposit as copper metal: Cu²⁺(aq) + 2e⁻ → Cu(s).

9. What is the difference between oxidation and reduction?

Answer: Oxidation is the loss of electrons; reduction is the gain of electrons.

10. Define oxidising agent and reducing agent.

Answer: An oxidising agent causes oxidation and itself undergoes reduction. A reducing agent causes reduction and itself undergoes oxidation.

11. Why does zinc act as the anode in a Daniell cell?

Answer: Zinc is more reactive than copper and loses electrons more readily. Therefore, it undergoes oxidation and acts as the anode.

12. Why is copper the cathode in a Daniell cell?

Answer: Copper ions accept electrons at the copper electrode and are reduced to copper metal. Hence, the copper electrode is the cathode.

13. Why is a Daniell cell called a galvanic cell?

Answer: It produces electrical energy from a spontaneous chemical reaction.

14. Why does copper get deposited when placed in silver nitrate solution?

Answer: Copper is more reactive than silver. It displaces silver from silver nitrate solution, and silver ions are reduced to metallic silver.

15. Why can silver nitrate solution not be stored in a copper vessel?

Answer: Copper reacts with silver nitrate and displaces silver from the solution. The copper vessel reacts and silver deposits on its surface.

16. What is the function of a galvanometer in a Daniell cell experiment?

Answer: It detects the presence and direction of a small electric current in the circuit.

17. What is the direction of electron flow in a Daniell cell?

Answer: Electrons flow from the zinc electrode to the copper electrode through the external wire.

18. What is the direction of conventional current in the external circuit?

Answer: Conventional current flows from copper towards zinc, opposite to electron flow.

19. What is the cell reaction of a Daniell cell?

Answer: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s).

20. What is the approximate standard voltage of a Daniell cell?

Answer: Approximately 1.10 V.

21. What is electrolysis?

Answer: Electrolysis is the process in which an electrolyte undergoes chemical changes when an electric current passes through it.

22. Why can molten sodium chloride conduct electricity?

Answer: In molten sodium chloride, Na⁺ and Cl⁻ ions are free to move and carry electric charge.

23. Why does solid sodium chloride not conduct electricity readily?

Answer: Its ions are fixed in the crystal lattice and cannot move freely to carry charge.

24. What are the products of electrolysis of molten sodium chloride?

Answer: Sodium metal at the cathode and chlorine gas at the anode.

25. What are the products of electrolysis of acidified water?

Answer: Hydrogen gas at the cathode and oxygen gas at the anode.

26. Why is hydrogen volume twice oxygen volume during electrolysis of water?

Answer: The equation 2H₂O → 2H₂ + O₂ shows a 2:1 gas volume ratio at the same temperature and pressure.

27. How can hydrogen gas be identified?

Answer: A burning splint brought near the test tube produces a characteristic pop sound.

28. What is the role of acid in electrolysis of water?

Answer: A small amount of suitable acid increases conductivity by providing ions; it is not the principal source of hydrogen and oxygen.

29. What is electroplating?

Answer: Electroplating is the process of coating an object with a thin layer of another metal by electrolysis.

30. Give four applications of electrolysis.

Answer: Extraction of reactive metals; manufacture of chemicals such as sodium hydroxide; electroplating; purification of metals such as copper.

31. Why is the object to be electroplated connected to the negative terminal?

Answer: It acts as the cathode. Positive metal ions gain electrons at its surface and deposit as metal.

32. Why is the plating metal connected to the positive terminal in the textbook copper-plating experiment?

Answer: It acts as the anode, undergoes oxidation, and releases metal ions into the electrolyte.

33. What happens to the copper plate during electroplating of an iron ring?

Answer: Copper atoms are oxidised to Cu²⁺ ions and enter the solution, causing the plate to lose mass.

34. What happens at the iron ring during copper electroplating?

Answer: Copper ions gain electrons and deposit as copper metal on the iron ring.

35. Why does copper-ion concentration remain approximately unchanged during copper electroplating?

Answer: Copper ions removed at the cathode are replenished by copper ions formed at the anode.

36. Name two metals commonly used for electroplating jewellery.

Answer: Gold and silver.

37. Give two advantages of electroplating.

Answer: It improves appearance and can protect the underlying metal from corrosion, depending on the coating and conditions.

38. What electrolyte is used for copper electroplating in the textbook experiment?

Answer: Copper sulphate (CuSO₄) solution.

39. What are the anode and cathode reactions during copper electroplating?

Answer: Anode: Cu → Cu²⁺ + 2e⁻. Cathode: Cu²⁺ + 2e⁻ → Cu.

40. What is the difference between electrolysis and electroplating?

Answer: Electrolysis is a process in which electrical energy brings about chemical changes. Electroplating is a specific application that deposits a metal coating on an object.

41. What is a primary cell? Give an example.

Answer: A primary cell is generally non-rechargeable. An ordinary dry cell is an example.

42. What is a secondary cell? Give two examples.

Answer: A secondary cell is rechargeable. Examples include a lead-acid accumulator and a lithium-ion battery.

43. Differentiate between primary and secondary cells.

Answer: Primary cells are generally non-rechargeable, e.g. ordinary dry cells. Secondary cells can be recharged and reused, e.g. lithium-ion batteries.

44. What is a fuel cell?

Answer: A fuel cell is a galvanic cell designed to convert the chemical energy of a fuel and an oxidant directly into electrical energy.

45. Mention two advantages of fuel cells.

Answer: They can produce electricity with high efficiency and can generate electricity continuously while fuel and oxidant are supplied.

46. Mention two uses of secondary cells.

Answer: Batteries in vehicles and rechargeable batteries in mobile phones, laptops and other electronic devices.

47. What is the energy function of an electrochemical cell?

Answer: An electrochemical cell converts chemical energy into electrical energy or, in an electrolytic system, uses electrical energy to drive chemical changes.

48. What is the main difference between galvanic and electrolytic cells in energy conversion?

Answer: A galvanic cell converts chemical energy into electrical energy, whereas an electrolytic cell uses electrical energy to bring about chemical change.

Section 9: Electroplating and Applications

1. Why is the object to be electroplated connected to the negative terminal of a battery?

Answer: The object acts as the cathode. Positive metal ions gain electrons at its surface and deposit as a thin metal layer.

2. Why is the plating metal connected to the positive terminal in the textbook copper-plating experiment?

Answer: The plating metal acts as the anode, undergoes oxidation and releases metal ions into the electrolyte.

3. What happens to the copper plate during electroplating of an iron ring?

Answer: Copper atoms lose electrons and enter the solution as Cu²⁺ ions, causing the plate to become thinner. Cu → Cu²⁺ + 2e⁻.

4. What happens at the iron ring during copper electroplating?

Answer: Cu²⁺ ions gain electrons and deposit as copper metal. Cu²⁺ + 2e⁻ → Cu.

5. Why does the copper-ion concentration remain approximately unchanged during copper electroplating?

Answer: Copper ions removed from the solution at the cathode are replenished by copper ions formed at the anode.

6. Name two metals commonly used for electroplating jewellery.

Answer: Gold and silver.

7. Give two advantages of electroplating.

Answer: It improves appearance and can protect the base metal from corrosion, depending on the coating.

8. What electrolyte is used for copper electroplating in the textbook experiment?

Answer: Copper sulphate (CuSO₄) solution.

9. What are the anode and cathode reactions during copper electroplating?

Answer: Anode: Cu → Cu²⁺ + 2e⁻. Cathode: Cu²⁺ + 2e⁻ → Cu.

10. What is the difference between electrolysis and electroplating?

Answer: Electrolysis uses electricity to bring about chemical change; electroplating is a specific use of electrolysis to coat an object with metal.

Section 10: Types of Cells and Fuel Cells

1. What is a primary cell? Give an example.

Answer: A primary cell is generally a non-rechargeable cell. An ordinary dry cell is an example.

2. What is a secondary cell? Give two examples.

Answer: A secondary cell is rechargeable. Examples include a lead-acid accumulator and a lithium-ion battery.

3. Differentiate between primary and secondary cells.

Answer: Primary cells are generally not rechargeable; secondary cells can be recharged and reused.

4. What is a fuel cell?

Answer: A fuel cell converts chemical energy from a fuel and an oxidant directly into electrical energy.

5. Mention two advantages of fuel cells.

Answer: They can produce electricity with high efficiency and can generate electricity while fuel and oxidant are supplied.

6. Mention two uses of secondary cells.

Answer: Vehicles and rechargeable electronic devices such as phones and laptops.

7. What is the main difference between galvanic and electrolytic cells?

Answer: A galvanic cell produces electrical energy from a spontaneous chemical reaction; an electrolytic cell uses electrical energy to drive a chemical reaction.

Section 11: Application-Based Questions

1. A zinc rod is dipped into copper sulphate solution. What happens?

Answer: Zinc displaces copper because it is more reactive. Copper deposits on the zinc and zinc ions enter the solution. Zn + CuSO₄ → ZnSO₄ + Cu.

2. A copper strip is placed in silver nitrate solution. Name the metal deposited and explain why.

Answer: Silver is deposited because copper is more reactive than silver and displaces it from solution.

3. An iron ring is to be coated with copper. Which electrode should the iron ring be, and why?

Answer: It should be the cathode connected to the negative terminal, because Cu²⁺ ions gain electrons and deposit on it.

4. During electrolysis of water, 20 mL of hydrogen is collected. Approximately how much oxygen is produced under the same conditions?

Answer: Approximately 10 mL, because the hydrogen-to-oxygen volume ratio is 2:1.

5. A metal reacts vigorously with dilute hydrochloric acid. What can you infer about its reactivity compared with copper?

Answer: It is generally more reactive than copper if it reacts vigorously while copper does not react under the same conditions.

6. A student observes that a copper plate becomes thinner during copper electroplating. Explain.

Answer: Copper atoms at the anode are oxidised to Cu²⁺ ions and enter the solution, causing the plate to lose mass.

7. Why does the solution near the cathode turn pink when phenolphthalein is added during electrolysis of aqueous sodium chloride?

Answer: Water is reduced at the cathode, producing OH⁻ ions. The solution becomes basic and phenolphthalein turns pink.

8. In a galvanic cell, what happens if the salt bridge is removed?

Answer: Charge accumulates in the half-cells, disrupting the cell reaction. The current decreases and eventually stops.

Section 12: Cell Comparison and Numerical Questions

Approximate cell voltages given in the supplied textbook pages:

1. In an Al–Cu cell, identify the anode and cathode.

Answer: Aluminium is the anode and copper is the cathode.

2. In an Ag–Cu cell, in which direction do electrons flow?

Answer: From copper to silver. Copper is the anode and silver is the cathode.

3. Which cell in the table has the highest voltage?

Answer: The Mg–Cu cell, approximately 2.7 V.

4. Write the anode reaction for an Mg–Cu cell.

Answer: Mg(s) → Mg²⁺(aq) + 2e⁻.

5. Write the cathode reaction for an Mg–Cu cell.

Answer: Cu²⁺(aq) + 2e⁻ → Cu(s).

6. Write the overall cell reaction for an Mg–Cu cell.

Answer: Mg(s) + Cu²⁺(aq) → Mg²⁺(aq) + Cu(s).

7. Write the anode reaction for an Ag–Cu cell.

Answer: Cu(s) → Cu²⁺(aq) + 2e⁻.

8. Write the cathode reaction for an Ag–Cu cell.

Answer: 2Ag⁺(aq) + 2e⁻ → 2Ag(s).

9. Write the overall reaction for an Ag–Cu cell.

Answer: Cu(s) + 2Ag⁺(aq) → Cu²⁺(aq) + 2Ag(s).

Section 13: Higher-Order Thinking Questions

1. A student says, “The anode is always the positive electrode.” Is the statement correct?

Answer: No. The anode is negative in a galvanic cell and positive in an electrolytic cell. Oxidation always occurs at the anode.

2. A student says, “The cathode is always negative.” Is the statement correct?

Answer: No. The cathode is positive in a galvanic cell and negative in an electrolytic cell. Reduction always occurs at the cathode.

3. Why can a galvanic cell produce electricity without an external battery?

Answer: Its spontaneous redox reaction releases chemical energy that is converted into electrical energy.

4. Why are two separate half-cells used in a Daniell cell?

Answer: They separate oxidation and reduction so electrons travel through the external circuit, producing current.

5. Why is copper deposited at the cathode instead of remaining dissolved in the electrolyte?

Answer: Copper ions gain electrons at the cathode and become neutral copper atoms that deposit on the electrode.

6. A student connects the copper plate to the negative terminal and the iron ring to the positive terminal while trying to coat the ring with copper. What is wrong?

Answer: The connections are reversed. The iron ring should be the cathode connected to the negative terminal; the copper plate should be the anode connected to the positive terminal.

7. Why does copper act as a reducing agent when it reacts with silver nitrate solution?

Answer: Copper loses electrons and reduces Ag⁺ ions to silver metal, so copper is the reducing agent.

8. Why is silver ion an oxidising agent in the reaction between copper and silver nitrate?

Answer: Ag⁺ ions accept electrons from copper and are reduced to silver metal.

9. Why do ionic substances conduct electricity in aqueous solution but not usually in the solid state?

Answer: Their ions move freely in aqueous solution but are held in fixed positions in the solid crystal lattice.

10. Why is electroplating useful for objects made of inexpensive metals?

Answer: It improves appearance and can give the surface useful properties without making the whole object from an expensive metal.

Section 14: Important Exam Revision Points

• Anode = oxidation.
• Cathode = reduction.
• Oxidation = loss of electrons.
• Reduction = gain of electrons.
• Galvanic cell: chemical energy → electrical energy.
• Electrolytic cell: electrical energy → chemical change.
• Must-learn equations: Zn → Zn²⁺ + 2e⁻; Cu²⁺ + 2e⁻ → Cu; 2H₂O → 2H₂ + O₂; 2Cl⁻ → Cl₂ + 2e⁻; Cu + 2Ag⁺ → Cu²⁺ + 2Ag.
• Frequently tested topics: Daniell cell components and reactions; galvanic versus electrolytic cells; oxidising and reducing agents; electrolysis of water and sodium chloride; electroplating; primary, secondary and fuel cells.

Class 10 Biology Questions And Answers

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