Methods Manual
Controlled Document   
- MTH 95
- Ver 3
- 5/04/02

SOP: Standardisation of a 1M Potassium Permanganate Solution

Background
This procedure describes the standardisation of an approximately 1M solution of potassium permanganate (KMnO4) . The primary standard used is 2.000M sodium oxalate (Na2C2O4) that has been acidified with sulfuric acid.

The potassium permanganate solution is delivered slowly from a burette to a flask containing the acidified oxalate solution, until just enough KMnO4 has been added to react with all of the Na2C2O4. The reaction end-point is detected by the first appearance of a permanent pink colour to the solution. At this point all the Na2C2O4 in the flask has reacted and a trace of excess purple permanganate ions have been added, from the burette to the flask. These excess permanganate ions remain in solution, as there is no more sodium oxalate to react with, giving the solution in the flask a pink colour.

As the potassium permanganate is a deep purple colour, it is not possible to take readings on the burette from the bottom of the meniscus as is usual. The top of the meniscus will need to be used as the indication of the level in the burette. (A meniscus is the curved upper surface of a liquid in a container.)

All volumetric glassware used in this procedure is Class A. Standard PPE should be worn when performing this work.

Method

  1. Using a bulb pipette, quantitatively transfer a 25.00 mL aliquot of the 2.000M standard sodium oxalate solution to a 250 mL Erlenmeyer flask.

  2. Using a bulb pipette, add a 25.00 mL aliquot of 4M sulfuric acid to the Erlenmeyer flask.

  3. Wash down the inside of the flask with about 50 mL of distilled water delivered from a wash bottle and shake.

  4. Using a beaker, carefully fill a 50 mL burette with the potassium permanganate solution.

  5. Record the level in the burette, remembering to take the level at the top of the meniscus.

  6. Use a magnetic stirrer to stir the solution during the titration process.

  7. Titrate the acidified sodium oxalate solution to the first sign of a permanent pink end point (use a white tile beneath the Erlenmeyer flask during the titration).

  8. Record the level in the burette and calculate the titre of potassium permanganate used in the titration.

  9. Repeat the titration until three titres are obtained that agree within 0.01 mL. Average these readings, T(KMnO4).

  10. Calculate the molarity of the potassium permanganate solution M(KMnO4) to 4 significant figures using the following formula: