Would Tris ($\mathbf{2}\mathbf{,}\mathbf{2}\mathbf{\text{'}}\mathbf{-}$bipyridine)iron be a useful indicator for the titration of ${\mathbf{Sn}}^{\mathbf{2}\mathbf{‐}}$with $\mathbf{Mn}\left(\mathrm{EDTA}\right)$? (Hint: The potential at the equivalence point must be between the potentials for each redox couple)

• Indicators are weak acids or bases (typically derived from plant pigments) that have unique colors in their ionized and non-ionized states and are proportional to the pH of the solution being tested.

• A material that can be added to the reaction mixture to show the titration's equivalence point. pH is frequently measured with colored indicators.

First we can write reduction half-reactions and find their standard reduction potentials in appendix H:

$$\begin{gathered} {\mathrm{Sn}}^{1‐}+2{\mathrm{e}}^{‐}\xcancel{}{\mathrm{Sn}}^{2+}\mathrm{E}°=0.139\mathrm{V} \\ \mathrm{Mn}\left(\mathrm{EDTA}\right)+\mathrm{e}\xcancel{}\mathrm{Mn}{\left(\mathrm{EDTA}\right)}^2{\mathrm{E}}^{°}=0.825\mathrm{V} \end{gathered}$$

The potential of Tris ($2,2$'-Bipyridine) iron that shows the end point can be found in table $16-2$ and it is $1.120\mathrm{V}$.

Hence, the end point of the titration is in the range of $0.139\mathrm{V}$to $0.825\mathrm{V}$so Tris ($2,2$-Bipyridine)iron would not be useful for the titration since it has a higher end point potential.