4
$\begingroup$

Why is the cathodic reaction of $I^-/AgI/Ag$ is $$\ce{AgI + e- -> Ag + I-}$$ but not, $$\ce{Ag+ + e- -> Ag }$$

whereas, in $Ag/AgCl(s)$, $KCl$(0.2M); it is $$\ce{Ag+ + e- -> Ag}$$

$\endgroup$
6
$\begingroup$

The real reaction is $\ce{Ag+ + e- -> Ag}$ for both cases. Equation written in this way, ${E^0}$ will be equal to the reduction potential of Ag(I) in its 1 M solution.

If it is written as $\ce{AgI + e- -> Ag + I-}$, then ${E^0}$ will be equal to the reduction potential of Ag(I) in 1 M $\ce{I-}$ solution -or in other terms in ${K_{sp}(AgI)}$ Molar Ag(I). solution

Hence, technically, $\ce{Ag+ + e- -> Ag}$ is same with $\ce{AgI + e- -> Ag + I-}$. Latter is more descriptive and practically more relevant, however, because the presence of $\ce{I- /Cl-}$ ions in the medium limits the amount of $\ce{Ag+}$ cations via ${K_{sp}}$ and the notation readily implies this.

$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.