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Quiz Chapter 1: Redox Equilibrium

10 questions · Form 5 Chemistry Bab 1: Redox Equilibrium

10 questions · plays in fullscreen

Full Question List & Answer Key

Prefer reading to quizzing? All 10 questions are listed below with the answer and explanation under each one.

1. During the electrolysis of concentrated sodium chloride solution, why is chlorine gas produced at the anode instead of oxygen?

  1. The concentration of Cl⁻ ions is significantly higher than OH⁻ ions
  2. Cl⁻ ions have a lower E° value than OH⁻ ions
  3. Carbon electrodes attract Cl⁻ ions exclusively
  4. Oxygen gas dissolves in the electrolyte immediately
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Answer: A

When using concentrated halide solutions, the high concentration factor overrides the standard electrode potential factor, causing Cl⁻ ions to discharge preferentially.

2. A substance that acts as an oxidising agent will always:

  1. Lose electrons and undergo oxidation
  2. Gain electrons and undergo reduction
  3. Increase its oxidation number
  4. Donate protons to the solution
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Answer: B

An oxidising agent oxidises other substances by accepting/gaining electrons, meaning it undergoes reduction.

3. The standard electrode potentials (E°) for Zn²⁺/Zn and Cu²⁺/Cu are -0.76 V and +0.34 V respectively. What is the E°cell for a Zn-Cu cell?

  1. -0.42 V
  2. +0.42 V
  3. -1.10 V
  4. +1.10 V
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Answer: D

E°cell = E°cathode - E°anode = (+0.34 V) - (-0.76 V) = +1.10 V.

4. Which of the following reaction is NOT a redox reaction?

  1. Zn + 2HCl → ZnCl₂ + H₂
  2. AgNO₃ + NaCl → AgCl + NaNO₃
  3. 2Mg + O₂ → 2MgO
  4. Cl₂ + 2KBr → 2KCl + Br₂
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Answer: B

Double displacement reactions like AgNO₃ + NaCl → AgCl + NaNO₃ involve no change in oxidation numbers for any element.

5. Which metal can be extracted from its oxide by reduction with carbon in a blast furnace?

  1. Aluminium
  2. Magnesium
  3. Iron
  4. Potassium
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Answer: C

Iron is less reactive than carbon, so carbon can reduce iron(III) oxide to iron in a blast furnace. Metals like Al, Mg, and K are more reactive than carbon and require electrolysis.

6. In a voltaic cell, at which electrode does oxidation occur?

  1. Cathode
  2. Salt Bridge
  3. Anode
  4. External wire
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Answer: C

Oxidation always takes place at the anode in both voltaic and electrolytic cells.

7. Which of the following reagent converts Fe²⁺ ions to Fe³⁺ ions?

  1. Zinc powder
  2. Acidified Potassium Dichromate(VI) solution
  3. Sulfur dioxide gas
  4. Magnesium ribbon
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Answer: B

Acidified Potassium Dichromate(VI) is a strong oxidising agent capable of oxidising Fe²⁺ to Fe³⁺.

8. In the reaction Fe²⁺ + Ce⁴⁺ → Fe³⁺ + Ce³⁺, which species acts as the reducing agent?

  1. Ce⁴⁺
  2. Fe³⁺
  3. Ce³⁺
  4. Fe²⁺
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Answer: D

Fe²⁺ loses an electron to form Fe³⁺ (oxidation state increases from +2 to +3), so it undergoes oxidation and acts as the reducing agent.

9. What happens to the blue color of copper(II) sulfate solution when a zinc strip is immersed in it?

  1. Turns darker blue
  2. Fades gradually until colorless
  3. Turns bright yellow
  4. No change in color
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Answer: B

Zinc reduces Cu²⁺ ions (which cause the blue color) into solid Cu copper deposit, reducing the Cu²⁺ concentration and causing the blue color to fade.

10. In the purification of copper by electrolysis, what material should be used as the anode?

  1. Pure copper
  2. Impure copper
  3. Platinum
  4. Graphite
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Answer: B

The impure copper is made the anode so it dissolves into Cu²⁺ ions during electrolysis.

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