Hydrogen peroxide decomposition using different catalysts

Your shopping list might look strange, but this practical will be well worth it. Supporting student to understand reaction rates, catalysis, and enzymes.

This experiment should take 5 minutes.

Equipment 

Apparatus

• Eye protection
• Measuring cylinders, 250 cm³, x1 for each catalyst
• Large tray for spills
• Stopwatch

Chemicals

• Hydrogen peroxide solution, 75 cm³,100 vol
• Powdered manganese(IV) oxide (manganese dioxide, MnO₂), 0.5 g
• Lead(IV) oxide (lead dioxide, PbO₂), 0.5 g
• iron(III) oxide (red iron oxide, Fe₂O₃), 0.5 g
• Potato, 1 cm³
• Liver, 1 cm³

Health, safety and technical notes

• Read our standard health and safety guidance.
• Always wear eye protection.
• Hydrogen peroxide is corrosive, see CLEAPSS Hazcard HC050.
• Manganese oxide is harmful if swallowed or inhaled, see CLEAPSS Hazcard HC060.
• Lead dioxide is a reproductive toxin, harmful if swallowed or inhaled, a Specific Target Organ Toxin and hazardous to the aquatic environment, see CLEAPSS Hazcard HC056.
• Avoid contact of the catalysts with aluminium and other metal powders, explosive reactions can occur.

Procedure

Before the demonstration

1. Line up five 250 cm³ measuring cylinders in a tray.
2. Add 75 cm³ of water to the 75 cm³ of 100 volume hydrogen peroxide solution to make 150 cm³ of 50 volume solution.

The demonstration

1. Place about 1 cm³ of washing up liquid into each of the measuring cylinders.
2. To each one add the amount of catalyst specified above.
3. Then add 25 cm³ of 50 volume hydrogen peroxide solution to each cylinder. The addition of the catalyst to each cylinder should be done as nearly simultaneously as possible – using two assistants will help.
4. Start timing.
5. Foam will rise up the cylinders.
6. Time how long each foam takes to rise to the top (or other marked point) of the cylinder.
7. The foam from the first three cylinders will probably overflow considerably.
8. Place a glowing spill in the foam; it will re-light, confirming that the gas produced is oxygen.

Notes

The lead dioxide will probably be fastest, followed by manganese dioxide and liver. Potato will be much slower and the iron oxide will barely produce any foam. This order could be affected by the surface areas of the powders.

Some students may believe that the catalysts – especially the oxides – are reactants because hydrogen peroxide is not noticeably decomposing at room temperature.

The teacher could point out the venting cap on the peroxide bottle as an indication of continuous slow decomposition.

Alternatively, s/he could heat a little hydrogen peroxide in a conical flask with a bung and delivery tube, collect the gas over water in a test-tube and test it with a glowing spill to confirm that it is oxygen.

This shows that no other reactant is needed to decompose hydrogen peroxide.

NB: Simply heating 50 volume hydrogen peroxide in a test-tube will not succeed in demonstrating that oxygen is produced. The steam produced will tend to put out a glowing spill. Collecting the gas over water has the effect of condensing the steam. It is also possible to ‘cheat’ by dusting a beaker with a tiny, almost imperceptible, amount of manganese dioxide prior to the demonstration and pouring hydrogen peroxide into it. Bubbles of oxygen will be formed in the beaker.

Theory

The reaction is :

2H₂O₂(aq) → 2H₂O(l) + O₂(g)

This is catalysed by a variety of transition metal compounds and also by peroxidase enzymes found in many living things.

Extension

• Repeat the experiment, but heat the liver and the potato pieces for about five minutes in boiling water before use.
• There will be almost no catalytic effect, confirming that the catalyst in these cases is an enzyme that is denatured by heat.
• Investigate the effect of using lumpy or powdered manganese dioxide.
• The powdered oxide will be more effective because of its greater surface area.
• Try using other metal oxides or iron filings as catalysts.
• Animal blood may be used instead of liver if local regulations allow this.
• One teacher suggested measuring the height of the foam over suitable time intervals and plotting a graph.