Question

The standard reduction potential of the $A{g}^{+}/Ag$ electrode at $298K$ is $0.799V$. Given that for$Agl,K_{sp}=8.7x10^{17}$, evaluate the potential of the $A{g}^{+}/Ag$ 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;
$[A{g}^{+}]=\sqrt{8.7\times 10^{-17}}M$
$=9.32\times 10^{-9}M$
$\Rightarrow E_{A{g}^{+}/Ag}=E^{\circ }-0.0592log\frac{1}{[A{g}^{+}]}$
$=0.799-0.0592\log \frac{1}{9.32\times 10^{-9}}=0.324V$
Also,for $Agl\rightleftharpoons A{g}^{+}{I}^{-};E^{\circ }=0.0592log{K}_{sp}$
$=-0.95V$
$Ag⟶A{g}^{+}+e^{-}{E}^{\circ }=-0.799V$
$\underline{Agl+e^{-}⟶Ag+I^{-}{E}^{\circ }=x}$
Adding: $Agl⟶A{g}^{+}+I^{-};E^{\circ }=-0.95V$
$=x-0.799$
$\Rightarrow x=-0.151V$