Question

A voltaic cell consists of an electrode of solid silver immersed in a 0.10 M
$AgN{O}_3$ solution and an electrode of unknown metal X immersed in a 0.10
M solution $X(N{O}_3{)}_2$. A porous barrier separates the two half of the
cell. Also given : $E_{\left(A{g}^{\oplus }/Ag\right)}^{\ominus }=0.80V$ and $E_{cell}^{\ominus }=1.05V$ at ${25}^{\circ }C$

$X\left(s\right)|X^{2+}\left(1.0M\right)||A{g}^{\oplus }\left(0.1M\right)|Ag\left(s\right)$

Which of the following statements regarding the cell and X is incorrect ?

• A. Standard EMF $\left(E^{\ominus }\right)$ of $X^{2+}|X$ is $0.25V$ at ${25}^{\circ }C$.
• B. X is a stronger reducing agent than $H_2\left(g\right)$.
• C. As the cell operates, the concentration of both $X^{2+}$ and $A{g}^{\ominus }$ increase in their respective half cells.
• D. As the cell operates, the concentration of $X^{2+}$ increases in the anode chamber while the concentration of $A{g}^{\oplus }$ decreases in the cathode chamber.

Answer 1

The correct option is C As the cell operates, the concentration of both $X^{2+}$ and $A{g}^{\ominus }$ increase in their respective half cells.

$E^{\ominus }A{g}^{\oplus }|Ag=0.8V;E_{X^{2+}|X}^{\ominus }=?;E^{\ominus }cell=1.05V$ Now, $E_{cell}^{\ominus }=(E_{A{g}^{\oplus }|Ag}^{\ominus }-E_{x^{2+}|X)}^{\ominus }$

$\Rightarrow E_{X^{2+}X}^{\ominus }=-0.25V$

Since, $E_{X^{2+}|X}^{\ominus }<E_{H^{\oplus }|H_2}^{\ominus }$, X is a stronger reducing agent than $H_2$.