Deck 6: Oxidation and Reduction

Question 1

Determine the oxidation states of sulfur in the following compounds (i) H₂S (ii) SO₂ and (iii) H₂SO₃.

A) (i) -2 (ii) +4 (iii) +6.
B) (i) +2 (ii) +4 (iii) + 6.
C) (i) -2 (ii) +4 (iii) +4.

Answer 1

C

Question 2

Find the correct statement:

A) Oxidizing agent oxidizes another species and is reduced during a redox reaction.
B) Half-reactions represent actual chemical processes
C) During a reduction process, a reducing agent releases electron(s).

Answer 2

A

Question 3

A redox reaction shifted to the right side when:

A) E⁰ = 0
B) E⁰ > 0
C) E⁰ < 0

Answer 3

B

Question 4

In an Ox/Red couple:

A) The more positive reduction potential is the more oxidizing Ox is.
B) The more positive reduction potential is the more reducing Red is.
C) The more negative reduction potential is the more oxidizing Ox is.

Question 5

Which of the following half-reactions should be affected by the change in H⁺ concentration:
(i) ClO₂^-(aq) + H₂O(l) + 2e^- → ClO^-(aq) + 2OH^-(aq)
(ii) MnO₂(s) + 4H⁺(aq) +2e^- → Mn²⁺(aq) + 2H₂O(l)
(iii) ½ Cl₂(aq) + e^- → Cl^-(aq)

A) (i) and (iii)
B) (ii) and (iii)
C) (i) and (ii)

Question 6

Find the correct statement about Latimer diagrams and one of their uses:

A) In Latimer diagrams the oxidation numbers increase from left to right; a species can disproportionate into its two neighbours if the potential on the right is more negative than the potential on the left.
B) In Latimer diagrams the oxidation numbers decrease from left to right; a species can disproportionate into its two neighbours if the potential on the right is more negative than the potential on the left.
C) In Latimer diagrams the oxidation numbers decrease from left to right; a species can disproportionate into its two neighbours if the potential on the right is more positive than the potential on the left.

Question 7

Which statement is the correct one?

A) Comproportionation is a redox reaction in which the oxidation number of an element is simultaneously raised and lowered. Disproportionation is the opposite of comproportionation.
B) Disproportionation is a reaction in which the oxidation number of an element is raised. Comproportionation is a reaction in which the oxidation number of an element is lowered.
C) Disproportionation is a redox reaction in which the oxidation number of an element is simultaneously raised and lowered. Comproportionation is the opposite of disproportionation.

Question 8

Which statement is correct in reference to the Frost diagrams?

A) The maximum point on the diagram gives the most stable species with respect to the oxidation state zero which is set as a minimum point on the diagram.
B) The minimum point on the diagram represents the most stable species with respect to the oxidation state zero which is set at 0 on the diagram.
C) The maximum point on the diagram has the highest stability, and the lowest point, set at 0, corresponds to the least stable species.

Question 9

Find the correct statement(s) concerning the Pourbaix diagrams:
(i) A horizontal line separates species related by proton transfer only
(ii) A vertical line separates species related by electron transfer only
(iii) Sloped lines separate species related by both electron and proton transfer.

A) All are correct
B) (i) and (ii)
C) Only (iii)

Question 10

According to Ellingham diagram, the reduction of Al₂O₃ with carbon is feasible above 2400 $\degree$ C, why is Al₂O₃ reduced in practice electrochemically rather than chemically with carbon?

A) The temperature is too high and maintaining it is too expensive.
B) It is difficult to achieve correct Al₂O₃-to-carbon ratio in practice.
C) Formed Al is reducing enough to reduce CO and CO₂ back to carbon.