Inquiry Lab
The Potentiometric Titration of
Hydrogen Peroxide
8
The hydrogen peroxide sold over the counter is labeled as 3% mass/volume. Your mission is to
determine what the actual percentage of the hydrogen peroxide is. The method you will use to
determine the concentration is by titration with a solution of potassium permanganate, KMnO4.
OBJECTIVES
In this experiment, you will

Conduct the potentiometric titration of the reaction between commercially available
hydrogen peroxide and potassium permanganate.
 Measure the potential change of the reaction.
 Determine the concentration of the hydrogen peroxide solution.
Prelab
Determine the safety data for all chemicals used in this lab.
Write and balance the oxidation half reaction for hydrogen peroxide.
What are the oxidation states of oxygen in the reaction?
Write and balance the reduction half reaction of MnO4- to Mn2+.
What are the oxidation states of manganese in the reaction?
Write and balance the total redox equation for this reaction.
How many electrons are transferred in this reaction?
Determine Eocell for the reaction. (the reduction potentials are in your book)
MATERIALS
Chemical needed
3% hydrogen peroxide, H2O2, solution
potassium permanganate, KMnO4, solution, in H2SO4
4.5 M sulfuric acid, H2SO4, solution
Concentration Calculations
1. 3% is mass percent by volume or 3.0 g hydrogen peroxide /100 mL of solution. Convert
that to molarity.
2. In order to make this reaction work, we will dilute our hydrogen peroxide (so we don’t
run out) and acidify it (so the redox reaction will work). The reaction should work with
10 mL of 3% peroxide and 17 mL of 6M sulfuric acid diluted to 100 mL with distilled
water. Calculate the concentration of hydrogen peroxide and sulfuric acid in the resulting
solution.
3. MnO4- solutions are bright purple. Mn2+ is nearly colorless. I would prefer you keep the
permanganate solution in the beaker because it will be clear when you are done and easy
to clean. If the permanganate solution is in the burette, or reservoir of the drop counter, it
will be purple and difficult to clean.
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4. Titrations with a 60 mL burette work well if the equivalence point is around 30 mL.
Calculate the moles of potassium permanganate needed to reach the equivalence point if
the titrant is 3% hydrogen peroxide.
5. When making your initial solution of potassium permanganate, add sulfuric acid to
acidify the solution. The initial solution should be around 1 M H2SO4.
6. Write a procedure to determine the actual concentration of the hydrogen peroxide.
Prepare to discuss Q values from the first drop of titrant throughout the titration and the
qualitative effect on Ecell according the Nearst equation.
7. Follow your procedure and perform at least 3 trials
DATA TABLE
Trial 1
Trial 2
Trial 3
Volume of H2O2 solution used at
equivalence point (mL)
g of MnO4– in solution
DATA ANALYSIS
1.
2.
3.
4.
5.
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Calculate the actual moles of MnO4– in the beaker for each trial.
Use your answer to question 1, along with the balanced redox equation in the
introduction, to calculate the moles of H2O2in the sample of solution for each
trial.
Calculate the molar concentration of the H2O2 solution for each trial.
Compare your experimentally determined molarity of H2O2 to the label
description.
Convert the molarity back to a percent by volume
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