Find the emf of the cell in which the following reaction takes place at 298 KNi(s) + 2Ag^+ (0.001\ M) → Ni^2+ (0.001\ M) + 2Ag(s)(Given that E^°_cell = 10.5 V, 2.303 RT/F = 0.059 at 298 K)
1. 1.05 V
2. 1.0385 V
3. 1.385 V
4. 0.9615 V
1. 1.05 V
2. 1.0385 V
3. 1.385 V
4. 0.9615 V
Best answer
Answer: Dropped in the official answer key: full marks to every candidate
Key idea: use the Nernst equation \(E=E^\circ-\dfrac{0.059}{n}\log Q\).
Reaction: \(\mathrm{Ni+2Ag^+\to Ni^{2+}+2Ag}\), n = 2, \(Q=\dfrac{[\mathrm{Ni^{2+}}]}{[\mathrm{Ag^+}]^2}=\dfrac{10^{-3}}{10^{-6}}=10^3\).
\(E=E^\circ-\dfrac{0.059}{2}\times3=E^\circ-0.0885\) V.
The standard value is \(E^\circ=0.80-(-0.25)=1.05\) V, giving \(E=0.9615\) V (option 4). The paper prints \(E^\circ=10.5\) V, which gives 10.4115 V, not in any option.
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