Expt 021 -- Hydrogen Peroxide as an Oxidizing and a Reducing Agent

Hydrogen peroxide in acid solution is oxidized with KMnO₄ and reduced with KI.

Background

When H₂O₂ serves as an oxidizing agent, the oxygen is reduced to H₂O. When H₂O₂ serves as a reducing agent, the oxygen is oxidized to O₂ and bubbles are noticed.

Safety

The chemicals used are toxic. Sulfuric acid and hydrogen peroxide are corrosive. Wear goggles and apron. Avoid ingesting the chemicals. Wash hands after completing the experiment.

Procedure

1. Work in 4 wells of the plate that form a square.
2. Add 10 drops 2 % KI to the wells on one side of the square.
3. Add 10 drops 0.02 M KMnO₄ to the wells on the other side of the square.
4. Add 3 drops of 3 M H₂SO₄ to each of the 4 wells just used.

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5. Choose one side of the square that has one KI well and one KMnO₄ well. Add 3 % H₂O₂ to the KMnO₄ well until the pink color disappears. Add enough 3 % H₂O₂ to the KI well to get a deep color formation.

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6. Note and record the observations.

Questions

1. Write a balanced chemical equation for each reaction.

Handout Makeup

Name ___________________________ Class ________

Teacher__________________________

SmallScale 021 Hydrogen Peroxide as an Oxidizing and a Reducing Agent

Record the color changes observed during each reaction.

Answer the question.

Curriculum-

This experiment can be performed when studying oxidation and reduction. It also can fit in when discussion reaction conditions and reactions in general.

Safety-

The chemicals used are toxic. Sulfuric acid and hydrogen peroxide are corrosive. Wear goggles and apron. Avoid ingesting the chemicals. Wash hands after completing the experiment.

Time-

Teacher Preparation: 20 minutes

Class Time: 30 minutes

Materials-

• 1.5 mL of 2 % KI (dissolve 2 g KI in 98 mL of water.)
• 1.5 mL of 0.02 M KMnO₄ (dissolve 0.32 g KMnO₄ in enough water to make 100 mL of solution.)
• 3 mL of 3% H₂O₂ (use commercially available solution)
• 2.0 mL of 3 M H₂SO₄ (use as 3 M H₂SO₄ stock solution)
• 24-well plate
• plastic transfer pipets
• toothpicks

Disposal-

• Neutralize solutions containing Mn²⁺. Add KMnO₄ (forming MnO₂). Add 5% NaHSO₃ (also forming MnO₂), Filter. Discard the filtrate at the sink with excess water. Discard the solid precipitate with ordinary trash.
• Discard the iodide solutions at the sink.

Data Analysis-

• As an oxidizing agent:

  3 KI + H₂O₂ + H₂SO₄ --> KI₃ + K₂SO₄ + 2 H₂O

  or

  3 I^- + H₂O₂ + 2H⁺ --> I₃^- + 2 H₂O

• As a reducing agent:

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

  or

  2 MnO₄^- + 5 H₂O₂ + 6 H⁺ --> 5 O₂ + 2 Mn^2- + 8 H₂O

Reference-

Modified from a demonstration in the ChemSource Oxidation- Reduction module.

Key Words 1-

oxidation, reduction, redox, oxidizing agent, reducing agent, oxidant, reductant, chemical equation

Elements-

Mn I O