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Question

Examine the following half-reactions and select the strongest reducing agent among the species listed.
HgO(s) + H2O(l) + 2e- ↔ Hg(l) + 2OH-(aq) E° = 0.0977 V
Zn(OH)2(s) + 2e- ↔ Zn(s) + 2OH-(aq) E° = -1.25 V
Ag2O(s) + H2O(l) + 2e- ↔ Ag(s) + 2OH-(aq) E° = 0.342 V
B(OH)3(aq) + 7H+(aq) + 8e- ↔ BH4-(aq) + 3H2O(l) E° = -0.481 V
Hg(l)
Zn(s)
Ag(s)
BH4-(aq)
Zn(OH)2(s)




Examine the following half-reactions and select the strongest oxidizing agent among the species listed.
Cr2+(aq) + 2e- ↔ Cr(s) E° = -0.913 V
Fe2+(aq) + 2e- ↔ Fe(s) E° = -0.447 V
Sr2+(aq) + 2e- ↔ Sr(s) E° = -2.89 V
Co2+(aq) + 2e- ↔ Co(s) E° = -0.28 V
Cr2+(aq)
Fe(s)
Fe2+(aq)
Sr2+(aq)
Co2+(aq)

Answer 1

The strongest reducing agent is the species that is the most easily oxidized, so if we write the half-reactions as oxidations instead of reductions, and thus reverse the sign, the strongest reducing agent would have the highest Eo value, which is Zn (s).

Conversely, in the second group, the strongest oxidizing agent is the one that is the most easily reduced, so the one that has the highest Eo value, which is Co2+ (aq).