Peroxide Volcanoes in the Classroom

Peroxide Volcano

These experiments involve the use of peroxide of various concentrations, detergent and various organic and inorganic catalysts. The reaction essentially involves speeding up the natural decomposition of hydrogen peroxide into oxygen and water, according to the following equation:

2H2O2(l) --> 2H2O (l) + O2(g)

What is a Catalyst?

A catalyst is any substance that affects the rate of a chemical reaction. Most catalysts chemists are interested in are those that speed up reactions. They manage to do this by lowering the "activation energy" required to set the reaction in motion. This can be brought about by creating an alternate chemical pathway that requires less energy or by providing a surface or substrate that allows the reactant molecules to collide with each other more easily.

In the case of the decomposition of hydrogen peroxide, various catalyst can lower the required activation energy. Inorganic catalysts composed of compounds of the transition metals can be very effective in this regard. These include powdered manganese dioxide, potassium iodide, potassium sulphate and iron oxide. Organic catalysts such as yeasts, liver, blood and potatoes can also produce a similar, although often less spectacular, result. This is because they contain enzymes called "peroxidases" (or catalases) that naturally decompose hydrogen peroxide.

Making a Child-Friendly Peroxide Volcano – Materials and Teaching Method

The use of a lower strength peroxide solution and an organic catalyst may be a safer alternative for a primary classroom or for teachers with less science experience than others. This could involve a 3-6% hydrogen peroxide solution and the use of activated yeast as a catalyst for the decomposition reaction.

The following materials and equipment are required:

•                250ml plastic bottle (this could be modified to look like the cone of a volcano using papier mache or plasticine)

•                ½ cup 3% hydrogen peroxide solution

•                1 packet of active (live) yeast

•                ¼ cup detergent

•                warm water

•                food colouring

•                safety goggles

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Wearing safety goggles, add the hydrogen peroxide, detergent and food colouring to the plastic bottle. Mix these ingredients together by swirling the bottle. Place the bottle in a sink.

•                Mix the packet of active yeast with a small amount of warm water and allow to stand for around 5 minutes. This helps to activate the yeast cells.

•                Pour the yeast mixture into the plastic bottle and watch the results!

Note that the detergent is used to create a more spectacular foaming effect, as it combines with the bubbles of oxygen that are produced.

The following questions could be written on the board after students write up the experiment and their observations:

1.             What ingredient in this experiment acted as a catalyst to speed up the decomposition of hydrogen peroxide?

2.             Why was the packet of active yeast mixed with warm water?

Making a Heavier Duty Peroxide Volcano- Materials and Teaching Method

For a more dramatic display, 30% peroxide solution is used, with a transition metal compound acting as the catalyst. In this example, potassium iodide powder is added, but it could also be in the form of a saturated solution. Note that 30% hydroxide solution can cause burns and eye damage. In addition, adding too much potassium iodide can result in an over-vigorous reaction that may spray over everyone in the room.

The following materials and equipment are required:

•                50 mL 30% hydrogen peroxide

•                1 teaspoon potassium iodide powder

•                10ml detergent

•                food colouring

•                500ml glass measuring cylinder

•                safety goggles

•                rubber gloves

•                matches and wooden splint

Students should be instructed to copy down the following directions, which could be followed by a teacher-led explanation.

•                Put on the safety goggles and gloves.

•                Place the measuring cylinder on a large sheet of newspaper or plastic.

•                Add the hydrogen peroxide and detergent to the cylinder.

•                Squirt a small amount of food colouring down the inside wall of the measuring cylinder.

•                Add the potassium iodide and stand back.

Students should notice large volumes of coloured, foamy detergent pouring out of the cylinder. The teacher could demonstrate that the bubbles are oxygen gas by placing a glowing wooden splint inside the cylinder. The splint should re-light in the presence of such a large volume of oxygen. In addition, the teacher should indicate that this decomposition reaction is exothermic, meaning that heat is produced as a by -product.

The following questions could be written on the board after students write up the experiment and their observations. Note that potassium iodide, as with all catalysts, is not a reactant and therefore not consumed in the reaction.

1.             Write the equation for the decomposition of hydrogen peroxide.

2.             Why isn’t potassium iodide included in the above reaction?

3.             Explain why the glowing splint re-ignited when placed in the measuring cylinder.

4.             Is this reaction exothermic or endothermic? Explain.

Peroxide Volcano Follow -Up Activities

This reaction can be repeated without using detergent. When carried out in a 250ml plastic bottle it results in greyish steam shooting out of the container. This could be used to model the hot steam and ash that emanates from some volcanoes.

The demonstration can also be turned into a controlled experiment by varying the concentration of peroxide used or the type or amount of catalyst added. An interesting experiment designed by the Royal Society of Chemistry compares the rate of production of oxygen bubbles produced using metallic compounds, liver and potato as catalysts for the decomposition reaction.

Students should conclude from these activities that hydrogen peroxide decomposition is rapidly accelerated in the presence of inorganic or organic catalysts, producing large amounts of heat and oxygen gas. The catalysts, themselves, however, are not consumed in the reaction.

References

The Royal Society of Chemistry, "Catalysts for the Decomposition of Hydrogen Peroxide," rsc.org

Using Hydrogen Peroxide.com, 2007.

Woodrow Wilson Leadership Program in Chemistry, "The Effect of a Catalyst on the Rate of a Reaction," woodrow.org, 1986.

Woodrow Wilson National Fellowship Foundation, "Comparison of the Effects of Inorganic Catalysts and Enzymes on Peroxide Decomposition," woodrow.org, 1988.