GATE 2023 MT – Question 62
An aqueous solution contains Fe$^{2+}$ at $10^{-4}$ M, 298 K, and atmospheric pressure. The iron reduction potential is ______ V (two decimal places). Given: $E^\circ_{\mathrm{Fe}^{2+}/\mathrm{Fe}}=-0.44$ V, $F=96500$ C per mole of electrons, and $R=8.314$ J mol$^{-1}$ K$^{-1}$.
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Correct answer: -0.58 to -0.54
Explanation
Nernst gives $E=E^\circ+(RT/2F)\ln[\mathrm{Fe}^{2+}]$ for unit solid-iron activity.
Thus $E=-0.44+[8.314(298)/(2\times96500)]\ln(10^{-4})=-0.5582$ V. Rounded answer: **−0.56 V**.