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Physical Chemistry
March 14, 2025 | UR Gate

Decomposition of Hydrogen Peroxide by a Catalyst


Purpose of the Experiment:

  1. Determine the reaction rate constant (K).
  2. Determine the half-life (t₁/₂).
  3. Identify the order of the reaction.

Theoretical Principle:

The rate of a chemical reaction depends on several factors, including the concentration of reactants, temperature, and the presence and nature of a catalyst, among others.

A catalyst significantly increases the reaction rate. In this experiment, hydrogen peroxide decomposes according to the following equation:
2H2O2 → 2H2O + O2

A catalyst significantly increases the reaction rate. In this experiment, hydrogen peroxide decomposes according to the following equation:

The reaction rate can be increased by adding manganese dioxide ( MnO2 ) as a catalyst. The progress of the reaction can be monitored by determining the remaining concentration of hydrogen peroxide through titration with a standard potassium permanganate solution in an acidic medium, as represented by the following equation:

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

The decomposition of hydrogen peroxide in the presence of manganese dioxide ( MnO2 ) follows a first-order reaction. The rate equation for a first-order reaction is given by:

Where:
  • a = initial concentration of hydrogen peroxide at t = 0
  • X = amount of decomposed hydrogen peroxide at time t
  • a − x = remaining (unreacted) hydrogen peroxide
  • k = reaction rate constant

Integrating equation (1) gives:

Alternatively,


Materials Used:

  1. 0.2 N Potassium Permanganate ( KMnO4 ) solution
  2. 1% Hydrogen Peroxide ( H2O2 ) solution
  3. 2 N Sulfuric Acid ( H2SO4 ) solution
  4. 0.03 g Manganese Dioxide ( MnO2​ )

Apparatus Used:

  1. Graduated pipette
  2. Burette
  3. Conical flask
  4. Reaction flask
  5. Stopwatch

Experimental Procedure:

  • Prepare 100 ml of 0.2 N potassium permanganate solution, 100 ml of 1% hydrogen peroxide solution, and 100 ml of 2 N sulfuric acid solution.
  • Take 10 ml of hydrogen peroxide and add 10 ml of sulfuric acid, then titrate with potassium permanganate.
  • Add 0.03 g of manganese dioxide to 90 ml of hydrogen peroxide solution at room temperature, shake the mixture, and immediately start timing.
  • After four minutes, take a 10 ml sample of the mixture, add 10 ml of sulfuric acid, and titrate with 0.2 N potassium permanganate.
  • Repeat the previous step every four minutes for 5-6 titration cycles.

Results and Calculations:

Note:
This is an illustrative example performed in the laboratory.

V0 = 7



Graphical Representation:


Discussion:

Q: What factors affect the reaction rate in this experiment?
A: The reaction rate depends on the concentration of reactants, the surface area of the solid catalyst, and its physical and chemical properties.


Q: Is the catalyst in this experiment heterogeneous?
A: Yes, because it exists in a phase different from the reactant. The catalyst is solid, while the reactant is in liquid form.


Q: Can hydrochloric acid be used instead of sulfuric acid?
A: Yes, it can.


Q: What is hydrogen peroxide?
A: Hydrogen peroxide ( H2O2 ) is a chemical compound with a pale blue color in its pure form, appearing colorless in dilute solutions. It is slightly more viscous than water. Hydrogen peroxide is a weak acid but a strong oxidizing agent, making it effective for bleaching. It is sold in pharmacies as an antiseptic at a 3% concentration and in beauty supply stores at concentrations of 20-25%.


Q: Does the volume dispensed from the burette increase during titration?
A: No, it does not increase.


Q: What type of titration is used in this experiment?
A: Redox titration (oxidation-reduction).


Q: What are the physical and chemical properties of hydrogen peroxide?

Physical properties:
  • A transparent, odorless, colorless liquid.
  • Melting point: -43°C.
  • Easily supercooled without freezing.
  • Boiling point: 150°C.
  • Miscible with water in all proportions.
  • Forms hydrated crystals ( H2O2, 2H2O )
  • Dissolves salts effectively, similar to water.
Chemical properties:
  • Acts as an oxidizing and reducing agent.
  • Shows acidic properties.
  • Forms complex compounds.
  • In acidic media, it oxidizes iodide ions ( I− ) into iodine ( I2​ ) and forms potassium sulfate ( K2SO4​ ) and water.


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