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Quiz Chapter 1: Redox Equilibrium

10 questions · Form 5 Chemistry Bab 1: Redox Equilibrium

Question 1 of 10Score: 0

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

Full Question List & Answer Key

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

1. 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.

2. 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⁺.

3. 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.

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. 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.

6. Which of the following is the chemical formula of rust?

  1. FeO
  2. Fe₃O₄
  3. Fe(OH)₂
  4. Fe₂O₃·xH₂O
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Answer: D

Rust is chemically known as hydrated iron(III) oxide, represented as Fe₂O₃·xH₂O.

7. What are the essential conditions required for iron to rust?

  1. Water and Nitrogen
  2. Carbon dioxide and Oxygen
  3. Water and Oxygen
  4. Acid and Sunlight
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Answer: C

Rusting of iron requires simultaneous presence of water and oxygen.

8. Consider the half-equation: Cr₂O₇²⁻ + 14H⁺ + 6e⁻ → 2Cr³⁺ + 7H₂O. What is the change in oxidation number of chromium?

  1. +6 to +3
  2. +7 to +3
  3. +12 to +6
  4. +3 to 0
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Answer: A

In Cr₂O₇²⁻, Cr has an oxidation state of +6. In Cr³⁺, Cr has an oxidation state of +3. The change is from +6 to +3.

9. 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.

10. Which metal is used as a sacrificial anode to protect underground iron pipes from rusting?

  1. Copper
  2. Tin
  3. Magnesium
  4. Silver
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Answer: C

Magnesium has a more negative E° value than iron, making it more electropositive. It corrodes preferentially, protecting the iron.

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