The standard reduction potential for the process: [Co(H2O)6]^3+ + e^– - [Co(H2O)6]^2+ is 1.8 V. The standard reduction potential for the process: [Co(NH3)6]^3+ + e^– - [Co(NH3)6]^2+ is 0.1 V. Which

Question

The standard reduction potential for the process: [Co(H2O)6]^3+ + e^– -> [Co(H2O)6]^2+ is 1.8 V. The standard reduction potential for the process: [Co(NH3)6]^3+ + e^– -> [Co(NH3)6]^2+ is 0.1 V. Which of the complex ion, [Co(H2O)6]^2+ or [Co(NH3)6]^2+ can be oxidized to the corresponding cobalt (III) complex, by oxygen, in basic medium, under standard condition? [Given: E°_O2\|OH– = 0.4 V]

Prashant Kotian · Accepted Answer

Correct answer: B. For oxidation by oxygen to be feasible, E°_cell = E°_cathode(O2) + E°_anode(complex) must be positive. For [Co(H2O)6]^2+, E°_ox = -1.8 V, so E°_cell = 0.4 - 1.8 = -1.4 V (non-spontaneous). For [Co(NH3)6]^2+, E°_ox = -0.1 V, so E°_cell = 0.4 - 0.1 = +0.3 V (spontaneous). Thus, only [Co(NH3)6]^2+ can be oxidized. Therefore, correct answer is B.

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