Q70 · CSIR-NET Chemistry, June 2012
Paper: CSIR-NET June 2012 · Subject: Physical Chemistry · Chapter: Electrochemistry · Topic: Nernst Cells · Marks: 2 · Difficulty: Medium
The correct Nernst equation for the concentration cell: \[ \mathrm{Pt}\left|\mathrm{H}_{2}(\mathrm{p})\right| \mathrm{HCl}\left(a_{ \pm}\right)_{1}|\mathrm{AgCl}(\mathrm{s})| \mathrm{Ag} \| \mathrm{Ag}|\mathrm{AgCl}(\mathrm{s})| \mathrm{HCl}\left(a_{ \pm}\right)_{2}|\mathrm{H}(\mathrm{p})| \mathrm{Pt} \]
without liquid junction would be (a)$\mathrm{E}=\frac{2 R T}{F} \ln \frac{\left(a_{ \pm}\right) 1}{\left(a_{ \pm}\right) 2}$
(b)$\mathrm{E}=\frac{2 R T}{F} \ln \frac{\left(a_{ \pm}\right) 2}{\left(a_{ \pm}\right) 1}$
(c)$\mathrm{E}=\frac{R T}{F} \ln \frac{\left(a_{ \pm}\right) 2}{\left(a_{ \pm}\right) 1}$
(d)$\mathrm{E}=\frac{R T}{2 F} \ln \frac{\left(a_{ \pm}\right) 2}{\left(a_{ \pm}\right) 1}$
Answer
Answer: B ✓ checked by 4AB · confidence medium
The source book printed C; on checking, B is correct — see the explanation.
Explanation
Without liquid junction the net change is transfer of HCl from activity (a±)₂ to (a±)₁, involving a±² terms. E = (2RT/F) ln[(a±)₂/(a±)₁] (b).
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