Would indigo tetrasulfonate be a suitable redox indicator for the titration of $\mathbf{Fe}{\left(\mathrm{CN}\right)}_{\mathbf{6}}^{\mathbf{4}\mathbf{-}}$with ${\mathbf{TI}}^{\mathbf{3}\mathbf{+}}$in 1MHCI? (Hint: The potential at the equivalence point must be between the potentials for each redox couple.)

• In an acid-base titration, indicators, and electrodes are commonly used to record the redox titration's end point.
• Redox indicator: A chemical that changes color when it transitions from an oxidized to a reduced state.

For the purpose of titration of $\mathrm{Fe}{\left(\mathrm{CN}\right)}_6^4$with${\mathrm{TI}}^{3+}$in$1\mathrm{MCHI}$, It has to be explained why indigo tetrasulfonate would be a good redox indicator.

To clarify, indigo tetrasulfonate will work as a redox indicator in the following titration.

Indigo tetrasulfonate has a typical potential of 0.36 V

The potential at the equivalence point must be in the middle of each redox couple's potential. $\mathrm{Fe}{\left[\mathrm{CN}\right]}_6^3-{\overline{)\mathrm{Fe}{\left[\mathrm{CN}\right]}_6^4,0.356;{\mathrm{TI}}^{3+}}}_{\mathrm{T}}^{‐‐}{\mathrm{TI}}^{+},0.77\mathrm{V}$

The endpoint potential would be between 0.356 and 0.77 V. However, approaching the potential of 0.36 V, indigo tetrasulfonate changes color. As a result, for this titration, the indicator would not be employed as a redox indicator.

The indigo tetrasulfonate was discovered to be unsuitable as a redox indicator for the titration of $\mathrm{Fe}{\left(\mathrm{CN}\right)}_6^4$with ${\mathrm{TI}}^{3+}$in 1MHCI .