Question

The standard reduction potential of the $Ag^+/Ag$ electrode at $298 \,K$ is $0.799 \,V$. Given that for$ Agl, K_{sp}= 8.7 x 10^{17}$, evaluate the potential of the $Ag^+/Ag$ electrode in a saturated solution of $Agl$. Also calculate the standard reduction potential of the $I^- / Agl/Ag$ electrode.

Answer 1

In a saturated Agl solution;
$ [Ag^+]=\sqrt{8.7 \times 10^{-17}}M$
$ = 9.32 \times 10^{-9}\, M $
$\Rightarrow E_{Ag^+/Ag}= E^\circ - 0.0592\, log\frac{1}{[Ag^+]}$
$ = 0.799 - 0.0592\, \log\, \frac{1}{ 9.32 \times 10^{-9}}=0.324\, V$
Also,for $ Agl \rightleftharpoons Ag^+ I^-; E^\circ = 0.0592\, log\, K_{sp} $
$ = - 0.95\, V$
$Ag \longrightarrow Ag^+ + e^- E^\circ = -0.799\, V $
$\underline{ Agl + e^- \longrightarrow Ag + I^- E^\circ =x}$
Adding: $Agl \longrightarrow Ag^+ + I^- ; E^\circ =-0.95\, V$
$ = x - 0.799$
$\Rightarrow x = -0.151\, V $