Permanganometric titration of hydrogen peroxide

general remarks

Hydrogen peroxide is usually treated as a strong oxidizer, but in the presence of even stronger oxidizer it can become a reducing agent:

H₂O₂ → O₂ + 2H⁺ + 2e^-

Permanganate in low pH is strong enough to quantitatively oxidize hydrogen peroxide to oxygen. This reaction is used for the determination of hydrogen peroxide concentration.

reaction

Reaction taking place during titration is

2MnO₄^- + 5H₂O₂ + 6H⁺ → 2Mn²⁺ + 5O₂ + 8H₂O

Note: this is an example of a real-life reaction that can't be balanced using algebraic method. This is not a limitation of the method, but reasons behind are beyond scope of this site.

sample size

For 0.02 M titrant and assuming 50 mL burette, aliquot taken for titration should contain about 0.060-0.077 g of hydrogen peroxide (1.7-2.3 millimoles).

end point detection

As usual in the case of permanganate titrations, pink color of excess permanganate is strong enough so that there is no need for any other end point indicators.

solutions used

To perform titration we will need titrant - 0.02 M potassium permanganate solution, concentrated sulfuric acid (diluted 1:4) and some amount of distilled water to dilute hydrogen peroxide sample.

procedure

Pipette aliquot of hydrogen peroxide solution into 500mL Erlenmeyer flask.
Dilute with distilled water to about 200 mL.
Add 20 mL of sulfuric acid (1:4) solution.
Titrate with permanganate solution until a faint pink color persists for 30 seconds.

result calculation

According to the reaction equation given above 1 mole of permanganate reacts with 2.5 mole of hydrogen peroxide and this ratio have to be used for titration result calculation.

To calculate hydrogen peroxide solution concentration use EBAS - stoichiometry calculator. Download determination of hydrogen peroxide concentration reaction file, open it with the free trial version of the stoichiometry calculator.

Click n=CV button above MnO₄^- in the input frame, enter volume and concentration of the titrant used. Click Use button. Read number of moles and mass of hydrogen peroxide in the titrated sample in the output frame. Click n=CV button in the output frame below hydrogen peroxide, enter volume of the pipetted sample, read hydrogen peroxide concentration.

sources of errors

Apart from general sources of titration errors, when titrating hydrogen peroxide we should pay special attention to titrant. Potassium permanganate solutions are not stable and they should be filtered and normalized every 2-3 months. As the end point is detected after excess titrant is added, it is worthwhile to perform a blind test and subtract blind test volume from the titration results.