Chapter 4: Problem 57

Which of the following are redox processes? (a) \(\mathrm{CO}_{2} \longrightarrow \mathrm{CO}_{3}^{2-}\) (b) \(\mathrm{VO}_{3} \longrightarrow \mathrm{VO}_{2}\) (c) \(\mathrm{SO}_{3} \longrightarrow \mathrm{SO}_{4}^{2-}\) (d) \(\mathrm{NO}_{2}^{-} \longrightarrow \mathrm{NO}_{3}^{-}\) (e) \(\mathrm{Cr}^{3+} \longrightarrow \mathrm{CrO}_{4}^{2-}\)

Short Answer

Expert verified

The reactions that involve redox processes are A and E (considering the extended definition of redox).

Step by step solution

Analyzing Reaction A

In the reaction \(\mathrm{CO}_{2} \longrightarrow \mathrm{CO}_{3}^{2-}\), the oxidation state of carbon stays the same (-4). However, oxygen's oxidation number decreases from -2 in \(\mathrm{CO}_{2}\) to -8/3 in \(\mathrm{CO}_{3}^{2-}\), this means oxygen gains electrons, hence reduction occurs. Therefore, this is a redox process.

Analyzing Reaction B

For \(\mathrm{VO}_{3} \longrightarrow \mathrm{VO}_{2}\), the overall oxidation number of vanadium decreases from +6 in \(\mathrm{VO}_{3}\) to +4 in \(\mathrm{VO}_{2}\), meaning reduction occurs. Oxygen also loses electrons, but since its oxidation number does not change, it is not an oxidation reaction. Therefore, as a whole, this is not a redox process.

Analyzing Reaction C

In the reaction \(\mathrm{SO}_{3} \longrightarrow \mathrm{SO}_{4}^{2-}\), sulfur's oxidation state changes from +6 to +2, hence reduction occurs. Again, Oxygen's oxidation number stays the same (-2), hence it does not undergo oxidation or reduction. Therefore, this reaction is not a redox process.

Analyzing Reaction D

For \(\mathrm{NO}_{2}^{-} \longrightarrow \mathrm{NO}_{3}^{-}\), the oxidation number of nitrogen increases from +3 in \(\mathrm{NO}_{2}^{-}\) to +5 in \(\mathrm{NO}_{3}^{-}\), meaning oxidation occurs. Conversely, Oxygen's oxidation number does not change indicating that it does not undergo oxidation or reduction. Thus, this is not a redox reaction due to the absence of a reduction process.

Analyzing Reaction E

Reaction \(\mathrm{Cr}^{3+} \longrightarrow \mathrm{CrO}_{4}^{2-}\) involves the oxidation number of chromium decreasing from +3 to +6, indicating oxidation. Oxygen's oxidation number does not change in this reaction. Hence, this is not a classical redox process. However, in the more extended definition of a redox process where only one species can undergo a change in oxidation number, this reaction would be considered a redox process.

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Short Answer

Step by step solution

Analyzing Reaction A

Analyzing Reaction B

Analyzing Reaction C

Analyzing Reaction D

Analyzing Reaction E

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