Standardization of permanganate solution for use in potentiometric titrations

0.1M potassium permanganate standardization against sodium oxalate

Sodium oxalate is probably the most important standard substance used in permanganometry. Oxalate is easily oxidized to carbon dioxide, according to the reaction equation:

5Na2C2O4 + 2KMnO4 + 8H2SO4 → 10CO2 + 8H2O + 5Na2SO4 + 2MnSO4 + K2SO4

First portions of titrant added are decolorizing slowly. To speed up reaction at the beginning solution can be heated to about 70°C. However, reaction is catalyzed by the presence of Mn2+ cations, so it gains speed later during titration.

Procedure to follow:

  • Weight exactly about 0.25-0.30g of dry sodium oxalate and transfer it to Erlenmayer flask.
  • Add 100 mL of distilled water and dissolve solid.
  • Add 60 mL of 1M sulfuric acid solution.
  • Heat up the solution to about 70°C.
  • Titrate adding small volumes of titrant and waiting each time till the solution decolorizes.
  • Close to titration end point add titrant dropwise, until a faint pink color persists for 30 seconds.

To calculate potassium permanganate solution concentration use EBAS - stoichiometry calculator. Download potassium permanganate standardization against sodium oxalate reaction file, open it with the free trial version of the stoichiometry calculator.

Enter sodium oxalate mass in the upper (input) frame in the mass edit field above Na2C2O4 formula. Click n=CV button below permanganate in the output frame, enter volume of the solution used, read solution concentration.

0.1M potassium permanganate standardization against arsenic trioxide

Chemical characteristics of the arsenic trioxide As2O3 make it a good candidate for a standard substance in many potentiometric methods, however, because of its toxicity it is used less and less frequently.

Arsenic oxide is dissolved in sodium hydroxide, producing sodium arsenite, which is oxidized to arsenate:

5Na3AsO3 + 2KMnO4 + 6HCl -> 2MnCl2 + 2KCl + 5Na3AsO4 + 3H2O

To speed up the reaction small amount of iodate or iodide is added.

Procedure to follow:

  • Weight exactly about 0.15-0.20g of dry arsenic trioxide and transfer it to Erlenmayer flask.
  • Add 20 mL of 1M sodium hydroxide solution and dissolve solid.
  • Dilute with 150 mL of distilled water.
  • Add 10 mL of concentrated hydrochloric acid.
  • Add 2-4 drops of about 0.001M KIO3 solution.
  • Titrate until a faint pink color persists for 30 seconds.

To calculate potassium permanganate solution concentration use EBAS - stoichiometry calculator. Download potassium permanganate standardization against arsenic trioxide reaction file, open it with the free trial version of the stoichiometry calculator.

Note, that to be consistent with the use of arsenic trioxide and its molar mass, reaction equation is not the one shown above, but

5As2O3 + 4MnO4- + 9H2O -> 4Mn2+ + 10AsO43- + 18H+

These are equivalent. Enter arsenic troxide mass in the upper (input) frame in the mass edit field above As2O3 formula. Click n=CV button below permanganate in the output frame, enter volume of the solution used, read solution concentration.

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last modified on October 27 2022, 21:28:33.

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