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Quiz Chapter 1: Redox Equilibrium

10 questions · Form 5 Chemistry Bab 1: Redox Equilibrium

Question 1 of 10Score: 0

What is oxidation defined as in terms of electron transfer?

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1. What is oxidation defined as in terms of electron transfer?

  1. Gain of electrons
  2. Loss of electrons
  3. Sharing of electrons
  4. No change in electrons
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Answer: B

Oxidation is defined as the loss of electrons during a chemical process.

2. 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.

3. 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.

4. 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.

5. 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.

6. 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.

7. 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.

8. 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.

9. 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.

10. What is the oxidation number of manganese in Potassium Permanganate (KMnO₄)?

  1. +7
  2. +2
  3. +4
  4. +6
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Answer: A

K(+1) + Mn + 4(O, which is -2) = 0 => 1 + Mn - 8 = 0 => Mn = +7.

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