Chemistry · Electrochemistry

JEE Advanced 2021 — Paper 2 — Question 12

Some standard electrode potentials at 298 K are given below:

Pb2+/Pb−0.13 VNi2+/Ni−0.24 VCd2+/Cd−0.40 VFe2+/Fe−0.44 V\begin{aligned} & \mathrm{Pb}^{2+} / \mathrm{Pb}-0.13 \mathrm{~V} \\& \mathrm{Ni}^{2+/} \mathrm{Ni}-0.24 \mathrm{~V} \\& \mathrm{Cd}^{2+} / \mathrm{Cd}-0.40 \mathrm{~V} \\& \mathrm{Fe}^{2+} / \mathrm{Fe}-0.44 \mathrm{~V} \end{aligned}

To a solution containing 0.001 M of X2+\mathbf{X}^{2+} and 0.1 M of Y2+\mathbf{Y}^{2+}, the metal rods X\mathbf{X} and Y\mathbf{Y} are inserted (at 298 K ) and connected by a conducting wire. This resulted in dissolution of X\mathbf{X}. The correct combination(s) of X\mathbf{X} and Y\mathbf{Y}, respectively, is(are) (Given: Gas constant, R=8.314 J K−1 mol−1\mathrm{R}=8.314 \mathrm{~J} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}, Faraday constant, F=96500Cmol−1\mathrm{F}=96500 \mathrm{C} \mathrm{mol}^{-1} )

  1. Option A:

    Cd and Ni

    Correct
  2. Option B:

    Cd and Fe

    Correct
  3. Option C:

    Ni and Pb

    Correct
  4. Option D:

    Ni and Fe

Answer: A, B, C

Step-by-step solution

A) Cd+Ni+2⟶Cd+2+Ni\mathrm{Cd}+\mathrm{Ni}^{+2} \longrightarrow \mathrm{Cd}^{+2}+\mathrm{Ni}

Ecell =0.40+(−24)−0.05912log⁡0.0010.1=0.16+0.05912×2=6.64+0.551=0.71(+ve)\begin{aligned} & E_{\text {cell }}=0.40+(-24)-\frac{0.0591}{2} \log \frac{0.001}{0.1} & =0.16+\frac{0.0591}{2} \times 2=6.64+0.551=0.71(+\mathrm{ve}) \end{aligned}

(B) Ecell =0.40+(−0.44)−0.5912log⁡0.010.1\mathrm{E}_{\text {cell }}=0.40+(-0.44)-\frac{0.591}{2} \log \frac{0.01}{0.1}

=−0.04+0.5912×2=−0.04+0.06=0.02(+ve)=-0.04+\frac{0.591}{2} \times 2=-0.04+0.06=0.02(+\mathrm{ve})

(C) Ecell =0.24+(−0.13)+.05912×2\mathrm{E}_{\text {cell }}=0.24+(-0.13)+\frac{.0591}{2} \times 2 =0.11+0.06=0.33(+ve)=0.11+0.06=0.33(+\mathrm{ve}) (D) Ecell =0.24+(−0.44)+0.05912×2\mathrm{E}_{\text {cell }}=0.24+(-0.44)+\frac{0.0591}{2} \times 2 =−0.20+0.06=−0.14(−ve)=-0.20+0.06=-0.14(-\mathrm{ve})

Answer key and solution verified before publishing.

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Exam
JEE Advanced 2021
Paper
Paper 2
Subject
Chemistry
Chapter
Electrochemistry
Topic
Nernst Equation and Electrochemical Series