Let us become familiar with method of performing the experiments on redox titrations between following pairs:
MnO- 4 versus Fe2+ and C2 O42-
I2/ KI versus S2 O3 2-ions
1. Titrations of MnO4 versus Fe2+ and C2O42-
chemical reaction involved in these titrations are
Some important points are:
• KMnO 4 solution is taken in burette.
• Solution of Fe2+ salt or C2O42- salts are taken in titration flask.
• Sufficient-dilute H2SO4 is added to titration flask to provide acidic medium.
• End point is from colourless solution to light pink colour.
• In case of C2O42- salt the solution in titration flask should be heated to about 60°C before the addition of KMnO4 solution to provide sufficient activation energy. (Follow Activity 32.1.)
2. Titration of I2 / KI versus S2O32- salt
The chermical reaction involved in this titration is
In this titration,
- I2 / KI solution is taken in burette.
- Aqueous solution of S2O32- salts is taken in the titration flask.
- Indicator used is freshly prepared starch solution.
- Indicator should be added towards the end of the
- titration when the solution acquires lime yellow colour.
- The end point is appearance of blue colour.