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Chemistry Grade 12 Unit 2: ELECTROCHEMISTRY

1. Which of the following best describes oxidation?
A) Gain of electrons
B) Decrease in oxidation number
C) Loss of electrons
D) Addition of hydrogen

✅ Answer: C
💡 Explanation: Oxidation is the loss of electrons or an increase in oxidation number. Remember OIL RIG: Oxidation Is Loss, Reduction Is Gain.

2. In the reaction: Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s), which species acts as the reducing agent?
A) Zn(s)
B) Cu²⁺(aq)
C) Zn²⁺(aq)
D) Cu(s)

✅ Answer: A
💡 Explanation: Zn loses electrons and is oxidized to Zn²⁺, causing Cu²⁺ to be reduced. The species that is oxidized acts as the reducing agent.

3. When balancing the half-reaction MnO₄⁻ → Mn²⁺ in acidic medium, how many electrons are gained?
A) 3
B) 5
C) 7
D) 2

✅ Answer: B
💡 Explanation: Mn changes from +7 in MnO₄⁻ to +2 in Mn²⁺, a decrease of 5 units, meaning 5 electrons are gained: MnO₄⁻ + 8H⁺ + 5e⁻ → Mn²⁺ + 4H₂O.

4. Which statement is TRUE about an electrolytic cell?
A) It converts chemical energy to electrical energy spontaneously
B) The anode is negative and the cathode is positive
C) It requires an external power source to drive a non-spontaneous reaction
D) Electrons flow from cathode to anode through the external circuit

✅ Answer: C
💡 Explanation: Electrolytic cells use electrical energy from an external source to force non-spontaneous redox reactions to occur.

5. During the electrolysis of concentrated aqueous sodium chloride, which ion is preferentially discharged at the anode?
A) Na⁺
B) H⁺
C) OH⁻
D) Cl⁻

✅ Answer: D
💡 Explanation: In concentrated NaCl solution, Cl⁻ ions are preferentially discharged over OH⁻ at the anode due to higher concentration, producing chlorine gas.

6. What is produced at the cathode during the electrolysis of aqueous copper(II) sulfate using inert electrodes?
A) Hydrogen gas
B) Oxygen gas
C) Copper metal
D) Sulfur dioxide

✅ Answer: C
💡 Explanation: Cu²⁺ ions are reduced at the cathode (Cu²⁺ + 2e⁻ → Cu) because copper is less reactive than hydrogen, so Cu²⁺ is discharged in preference to H⁺.

7. According to Faraday's First Law of Electrolysis, the mass of substance deposited at an electrode is directly proportional to:
A) The voltage applied
B) The quantity of electricity passed
C) The concentration of electrolyte
D) The temperature of the solution

✅ Answer: B
💡 Explanation: Faraday's First Law states that mass deposited (m) is proportional to charge (Q = I × t). Formula: m = ZIt, where Z is the electrochemical equivalent.

8. If the same quantity of electricity is passed through solutions of AgNO₃ and CuSO₄, what is the ratio of moles of Ag to Cu deposited? (Ag⁺ + e⁻ → Ag; Cu²⁺ + 2e⁻ → Cu)
A) 1:1
B) 2:1
C) 1:2
D) 4:1

✅ Answer: B
💡 Explanation: 1 mole of electrons deposits 1 mole of Ag; 2 moles of electrons deposit 1 mole of Cu. For the same charge (e.g., 2F), 2 mol Ag : 1 mol Cu → ratio 2:1.

9. Which industrial process uses electrolysis to extract a reactive metal from its molten ore?
A) Electroplating of chromium
B) Purification of copper
C) Extraction of aluminum from bauxite
D) Chlor-alkali process

✅ Answer: C
💡 Explanation: Aluminum is extracted by electrolysis of molten Al₂O₃ dissolved in cryolite (Hall-Héroult process) because aluminum is too reactive to be reduced by carbon.

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