University of Virginia Physics Department Decomposition of Hydrogen Peroxide A Physical Science Activity

2003 Virginia SOLs

• PS.1
• PS.5

Objectives

Students will

• observe a chemical change in a decomposition reaction;
• recognize one of the indicators of a chemical change (release of gas bubbles);
• analyze the relative density of the gas and its flammability using a glowing splint;
• gain practice in following skills: observing, identifying, interpreting results;
• write out and balance a chemical equation for the decomposition of hydrogen peroxide;
• recognize and use a catalyst in a chemical reaction to lower the activation energy;
• observe the expanded volume required by the reactants when a gas is produced and explain this using the particle model for matter.

Motivation for Learning

Background Information

Students should analyze the chemical formula for hydrogen peroxide (H₂O₂), with the teacher and discuss the possible products that could result from this as a reactant. It should become clear that only hydrogen gas (H₂), oxygen gas (O₂), or water (H₂O) are possible products. Introduce the concept of diatomic molecules as you discuss the possible formation of either hydrogen or oxygen gas.

A discussion should take place now concerning ways to start or speed up a chemical reaction. Heat, increasing surface area, agitation, and addition of a catalyst are all possibilities. In this case a catalyst will be used to lower the activation energy required for the reaction to occur.

Next, instruction should be given about how to test for and recognize certain gases produced in the lab. Hydrogen is lighter than air and makes a barking or squeaking sound when tested with a flaming wooden splint. Oxygen is about the same density as air and causes a glowing splint to burst into flame. Carbon dioxide is heavier than air and puts out a flame. Nitrogen also extinguishes flame.

Student Activity

To print out the Student Copy only, click here.

Materials

• large test tube
• large solid cork or rubber stopper
• 3% hydrogen peroxide solution
• several wooden splints
• matches
• a pinch of yeast
• goggles

Procedure

1. Pour about ¼ test tube full of hydrogen peroxide. Analyze the liquid.
2. Add about a pinch of yeast to the hydrogen peroxide. Shake it until well mixed and put the cork on the test tube.
3. Test the bubbles of gas foaming out of the solution with first a flaming, then with a glowing wooden splint. Keep relighting the splint until the reaction stops.
4. Analyze the product left in the test tube at the end. What do you think it is?
5. Clean up the test tube and be sure wooden splints are extinguished before disposing of them.

Students with Special Needs

All students should be able to participate in this activity.

Click here for further information on laboratories with students with special needs.

 

Assessment

1. Describe the odor, color, viscosity, and flammability of hydrogen peroxide.
   
   
   
   
   
   
   
   
2. What happened when you put the cork on the test tube? Using what you know about the particle theory for matter, explain why this happened.
   
   
   
   
   
   
   
   
3. What kind of gas was produced by this reaction? What evidence do you have to prove this?
   
   
   
   
   
   
   
   
4. What do you think was left in the test tube at the end? Describe some of its properties. Is it the same substance that you started with?
   
   
   
   
   
   
   
   
5. What role does the yeast play in this chemical reaction?
   
   
   
   
   
   
   
   
6. Write a chemical equation for this reaction, using coefficients to balance the equation if necessary.
   
   
   
   
   
   
   
   
7. What evidence do you have that this was a chemical change and not a physical change?