Redox processes (Second test)

For each question choose the answer you consider to be the best.

1. In which species does manganese have an oxidation state of +3?

A. MnSO₄

B. KMnO₄

C. Mn₂O₃

D. MnO₂

2. What change occurs to vanadium during the conversion of VO₃⁻(aq) to VO²⁺?

A. It undergoes reduction and its oxidation state changes from + 5 to +4

B. It undergoes reduction and its oxidation state changes from +3 to +2

C. It undergoes oxidation and its oxidation state changes from −1 to +2

D. It undergoes oxidation and its oxidation state changes from +6 to +2

3. Which are correct statements?

I. The oxidation state of oxygen in H₂O₂ is −1

II. The oxidation state of nitrogen in N₂H₄ is −2

III. The oxidation state of hydrogen in MgH₂ is −1

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

5. Which is correct about the following reaction?

2I⁻(aq) + Cl₂(aq) → I₂(aq) + 2Cl⁻(aq)

A. I⁻(aq) gains electrons and is reduced.

B. Cl₂(aq) loses electrons and is reduced.

C. I⁻(aq) loses electrons and is oxidized.

D. Cl₂(aq) gains electrons and is oxidized.

6. Which is the correct order of the decreasing oxidising ability of the group 17 elements (strongest oxidizing agent first)?

A. F₂ > Cl₂ > Br₂ > I₂

B. Cl₂ > Br₂ > I₂ > F₂

C. I₂ > Br₂ > Cl₂ > F₂

D. F₂ > I₂ > Br₂ > Cl₂

7. What is the coefficient for H⁺(aq) when the redox equation below is balanced ?

MnO₄⁻(aq) + Fe²⁺(aq) + H⁺(aq) → Fe³⁺(aq) + Mn²⁺(aq) + H₂O(l)

A. 2

B. 4

C. 5

D. 8

8. Which is the correct combination of statements for the following reaction?

Cr₂O₇²⁻ (aq) + 3H₂O₂(l) + 8H⁺(aq) → 2Cr³⁺(aq) + 3O₂ + 7H­₂O(l)

9. Which species will act as the reducing agent when the following two half-cells are connected under standard conditions?

Fe³⁺(aq) + e⁻ ⇌ Fe²⁺(aq) E = + 0.77 V

Cu⁺(aq) + e⁻ ⇌ Cu(s) E = + 0.52 V

A. Cu(s)

B. Cu⁺(aq)

C. Fe²⁺(aq)

D. Fe³⁺(aq)

10. Consider the following reactions which all occur in solution at room temperature.

Fe(s) + Cu²⁺(aq) → Fe²⁺ + Cu(s)

Mg(s) + Zn²⁺(aq) → Mg²⁺ + Zn(s)

Zn(s) + Fe²⁺(aq) → Zn²⁺ + Fe(s)

Which is the correct combination of the strongest oxidizing agent and the strongest reducing agent?

11. Consider the standard electrode potentials of the following reactions:

Cu²⁺(aq) + 2e⁻ ⇌ Cu(s) E = + 0.34 V

½ I₂(s) + e⁻ ⇌ I⁻(aq) E = + 0.54 V

What is the cell potential for the spontaneous reaction under standard conditions?

A. + 0.88 V

B. – 0.88 V

C. + 0.20 V

D. – 0.20 V

12. What will be the cell potential under standard conditions when the following two half-cells are connected?

Sn²⁺(aq) + 2e⁻ ⇌ Sn(s) E = − 0.14 V

Cr₂O₇²⁻(aq) + 14H⁺(aq) + 6e⁻ ⇌ 2Cr³⁺(aq) + 7H₂O(l) E = + 1.33 V

A. 0.91 V

B. 1.19 V

C. 1.47 V

D. 1.75 V

13. Which are used for electroplating a metal with silver?

I. An electrolyte containing Ag⁺(aq)

II. A positive electrode made of silver

III. A negative electrode made of silver

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

14. Which occur during the electrolysis of molten sodium chloride?

I. Chlorine gas forms at the positive electrode

II. Electrons flow through the molten liquid

III. Reduction occurs at the negative electrode

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

15. Which factors may affect the products of electrolysis?

I. The concentration of the aqueous electrolyte

II. The nature of the electrodes

III. The position of the ions in the electrochemical series

A. I and II only

B. I and III only

C. II and III only

D. I, II and III

16. A sample of 1.0 mol dm^-3 copper(II) sulfate solution was electrolysed for 1 hour using copper electrodes. Which change would have caused the largest increase in the amount of copper deposited.

A. Increasing the concentration of the copper(II) sulfate to 1.1 mol dm^-3

B. Increasing the current by 10%

C. Increasing the surface area of the electrodes by 10%

D. Changing the electrodes from copper to graphite

17. When the same quantity of electricity was passed through a dilute solution of sodium hydroxide and through a molten solution of lead bromide, 0.050 mol of lead was produced. What amount (in mol) of hydrogen gas was evolved?

A. 0.012

B. 0.025

C. 0.050

D. 0.100

18. During the electrolysis of aqueous sulfuric acid 2 g of hydrogen gas are produced. What mass (in grams) of oxygen gas will be formed at the other electrode at the same time?

A. 8

B. 16

C. 32

D. 64

19. Which statement concerning electrochemical cells is correct?

A. The reaction occurring in a voltaic cell is spontaneous.

B. The reaction occurring in an electrolytic cell is spontaneous.

C. The reaction occurring in a voltaic cell requires electrical energy.

D. The reaction occurring in an electrolytic cell produces energy.

20. Which statement is correct about how current is conducted in an electrolytic cell?

A. Electrons move through the electrolyte and the external circuit.

B. Ions move through the electrolyte and through the external circuit.

C. Ions move through the salt bridge and electrons move through the external circuit.

D. Ions move through the electrolyte and electrons move through the external circuit.

Answers

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