Question

Consider the following concentration cell : $Zn\left(s\right)|Z{n}^{2+}\left(0.024M\right)||Z{n}^{2+}\left(0.480M\right)|Zn\left(s\right)$ which of the following statements is/are correct?

• A. The EMF of the cell at ${25}^{\circ }C$ is nearly + 0.039 V.
• B. The EMF of the cell at ${25}^{\circ }C$ is nearly - 0.039 V.
• C. If water is added in LHE, so that the $\left[Z{n}^{2+}\right]$ is reduced to 0.012 M, the cell voltage increases.
• D. If water is added in LHE, so that the $\left[Z{n}^{2+}\right]$ is reduced to 0.012 M, the cell voltage decreases.

Answer 1

Answer: (A), (C)

The correct options are
A The EMF of the cell at ${25}^{\circ }C$ is nearly + 0.039 V.
C If water is added in LHE, so that the $\left[Z{n}^{2+}\right]$ is reduced to 0.012 M, the cell voltage increases.

Cell reaction : $Z{n}^{2+}\left(0.484M\right)\to Z{n}^{2+}\left(0.024M\right)$

$E_{cell}=0-\frac{0.059}{2}log\left(\frac{0.024}{0.480}\right)=0.039V$

For : $Z{n}^{2+}\left(0.024M\right)\to Z{n}^{2+}\left(0.012M\right)$

$\Rightarrow E_{cell}=0-\frac{0.059}{2}log\left(\frac{0.012}{0.48}\right)$

$=0.03\times 1.6=0.048V$.

Hence, options A and C are correct.