What is the standard reduction potential (E^ ) for Fe^ 3+ Fe ? Given that Fe^ 2+ + 2e^- Fe ; E^ _ Fe^ 2+ /Fe = -0.47 V and Fe^ 3+ + e^- Fe^ 2+ ; E^ _ Fe^ 3+ /Fe^ 2+ = +0.77 V.

JEE Main 2017 Chemistry question

What is the standard reduction potential () for ? Given that \mathrm{Fe^{2+} + 2e^- \to Fe};\ E^\circ_{\mathrm{Fe^{2+}/Fe}} = -0.47 V and \mathrm{Fe^{3+} + e^- \to Fe^{2+}};\ E^\circ_{\mathrm{Fe^{3+}/Fe^{2+}}} = +0.77 V.

(1) VCorrect
(2) V
(3) V
(4) V

Answer: (1)

Solution

Electrode potentials are **not** additive when half-reactions are combined — Gibbs energies are. Using for each step:

\mathrm{ + → }: Δ ° = -(1)F(0.77) = -0.77F

\mathrm{ + → Fe}: Δ ° = -(2)F(-0.47) = +0.94F

Adding the two h

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Question ID VK-115812