Use this list of half-reactions to answer the following question(s). MnO_4^-(aq)

Question

Use this list of half-reactions to answer the following question(s). MnO_4^-(aq) + 8H^+(aq) + 5e^- rightarrow Mn^2+(aq) + 4H_2O(l) +1.51 V Cr_2O_7^2-(aq) + 6e^- rightarrow 2Cr^3+(aq) + 7H_2O(l) +1.33 V Cu^2+(aq) + 2e^- rightarrow Cu(s) +0.34 V Pb^2+(aq) + 2e^- rightarrow Pb(s) -0.13 V Fe^2+(aq) + 2e^- rightarrow Fe(s) -0.44 V Al^3+(aq) + 3e^- rightarrow Al(s) -1.66 V Refer to Exhibit 19-1. Which of these combinations would result in reaction? Cu(s) and MnO_4^-(aq) Cr_2O_7^2-(aq) and MnO_4^-(aq) Pb(s) and Fe^2+(aq) Al^3+(aq) and Cr^3+(aq) Al^3+(aq) and Cu(s) a b c d e

Explanation / Answer

a. For, Cu and MnO4-, reduction potential of Cu2+ < MnO4-. So, Cu will oxidise and MnO4- will reduce.

Thus reaction will proceed.

b. For, Cr2O72- and MnO4-, the reaction will not proceed because both are being reduced which is not possible.

c. For, Pb and Fe2+, reduction potential of Fe2+ < Pb2+. So, Fewill oxidise and Pb2+ will reduce.

Thus reaction will not proceed.

d. For, Al3+ and Cr3+, reduction potential of Al3+ < Cr3+. So, Alwill oxidise and Cr3+ will reduce.

But according to question, it is asked if Cr3+ is being oxidised. So, it is wrong. The reaction will not proceed.

e. For, Al3+ and Cu, reduction potential of Al3+ < Cu. So, Alwill oxidise and Cu will reduce.

But according to question, it is asked if Cu is being oxidised. So, it is wrong. The reaction will not proceed.

Correct answers is A.

Only reaction a will proceed.

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