4. Redox titrations. a. (1 pt) Explain how a redox indicator works. Why is it im

Question

4. Redox titrations. a. (1 pt) Explain how a redox indicator works. Why is it important to consider the standard reduction potential of the indicator-what happens if it is more easily oxidized or reduced than the analyte? b. (1 pt) Explain why starch is not really a redox indicator. How does starch help you detect the end point of an iodimetric titration, and why is it OK to add the starch at the beginning unlike the iodometric titrations you did in lab? Why must starch solutions be freshly prepared?

Explanation / Answer

a) At certain potential value of the electrode the redox indicator will undergo a very clear color change.
As titration reaction takes place the electrode potential also changes, the indicator should not
get influenced by the reaction i.e) it should not get easily oxidized or reduced hence indicator's
potential is considered. If the redox indicator is easily oxidized or reduced than the analyte
then you will observe the color change way before the redox reaction goes to completion.

b) Starch is not redox indicator it is just used to detect iodine. Starch will help you to get
the exact endpoint of an iodimetric titration. In Iodometric titration starch and iodine
might remain intact until the equivalent point, this is why we add starch just before
the equivalent point whereas in iodimetric titration it is normal to add at the beginning
as the solution will turn blue at the equivalent point i.e) just after the addition of iodine.
Starch on hydrolysis might get reduced to glucose giving an error in the titration hence
freshly prepared starch is preferred.

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