Question

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)

Short answer

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.

Step-by-step solution

Definition of Indicators

• 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.

Find the Endpoint

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.