Analytical Procedures - Hydrogen Peroxide Concentration
December 20, 2001

Introduction

The potassium permanganate method is commonly used to determine the concentration of hydrogen peroxide.  A weighed sample is acidified and titrated with standard potassium permanganate solution until the first permanent pink colour persists for 30 seconds of longer.

5 H₂O₂ + 3 H₂SO₄ + 2 KMnO₄  ->  K₂SO₄ + 2 MnSO₄ + 8 H₂O + 5 O₂

This method cannot be used when organic or inorganic matter that reduce potassium permanganate are present.  Hydrochloric acid or other chloride ions are to be avoided as the permanganate will also oxidize chloride ions to chlorine and the titration will be subject to errors.  The presence of fluoride ions affects the permanganate titration and large proportions of calcium salts or titanic acid lead to low results.

Equipment

• 50 mL burrette
• Analytical balance to weigh to 0.1 mg
• Eye dropper
• 250 mL Erlenmeyer flasks
• Specimen vial 28 mm OD x 57 mm high

Reagents

• Demineralized or distilled water
• Potassium permanganate (0.10N KMnO₄) may be standardized against primary standard sodium oxalate
• 1:4 vol/vol sulphuric acid (pre-mixed and cooled)
• 1:1 HNO₃

Procedure

Preparation of Glassware

Use only new weighing vials and eye droppers

Treat new flasks overnight with 1:1 HNO₃ at room temperature and rinse 6 to 8 times with water. 

Do not use chromic acid cleaning solution on any glassware used for hydrogen peroxide testing.  Trace chromium ions are excellent catalytic agents for decomposing peroxide and they are extremely difficult to remove from glassware.

Preparation of Hydrogen Peroxide Samples

Measure about 100 mL of water into a 250 mL Erlenmeyer flask

Add 10 mL of 1:4 vol/vol sulphuric acid

Draw about 1 mL of hydrogen peroxide sample into a standard eye dropper.   Place the dropper into a specimen vial

Rapidly weigh and record the weight of the vial, dropper and hydrogen peroxide sample to (± 0.0002) g

Add 2 to 5 drops of the hydrogen peroxide sample from the dropper to the flash containing water and sulphuric acid.  The number of drops is a function of the concentration of hydrogen peroxide according to the following:

H₂O₂ Concentration             Number of Drops

30 wt%                                      5
35 wt%                                      4
50 wt%                                      3
70 wt%                                      2

Replace the dropper in the vial, rapidly re-weigh and record the new weight.

The sample weight will be the initial weight minus the final weight of the vial, eye dropper and sample.

Titration

Titrate with 0.10N KMnO₄ while stirring constantly.  As the end point is approached, add less KMnO₄ until the titration progresses by fractional drop increments.  The end-point is the first barely perceptible pink colour that persists for 30 seconds.

Estimate and record the volume of KMnO₄ solution used to 0.01 mL.   Apply a volume correction factor of ±0.1% per 5ºC deviation from 20ºC temperature.

Calculate the hydrogen peroxide concentration using:

% H₂O₂ = (mL x N x 0.01701 x 100) / (sample weight)