Enzymes are biological catalysts, they increase the speed of a chemical reaction. They are large protein molecules and these enzymes are very specific to certain reactions.  Hydrogen peroxide decomposes slowly in light to produce oxygen and water. There is an enzyme called catalase that can speed up (catalyse) this reaction.

Class practical

Hydrogen peroxide is used to detect the presence of enzymes in liver, potato and celery, which catalyse the decomposition of hydrogen peroxide, by detecting the presence of the oxygen gas formed.

Lesson organisation

A class experiment in which the different sources of catalase are tested for their effect on hydrogen peroxide solution. This should take no more than 20 - 30 minutes.

Apparatus Chemicals

Eye protection

Each working group will require:

Conical flasks (100 cm3), 3

Measuring cylinder (25 cm3)

Bunsen burner

Wooden splint

A bucket or bin for disposal of waste materials

Hydrogen peroxide solution, ‘5 volume’

Liver (small piece) (Note 1)

Potato (small piece) (Note 1)

Celery (small piece) (Note 1)

Refer to Health & Safety and Technical notes section below for additional information.

Health & Safety and Technical notes

Read our standard health & safety guidance

Wear eye protection. Students must be instructed NOT to taste or eat any of the foods used in the experiment. 

Hydrogen peroxide solution, H2O2(aq) - see CLEAPSS Hazcard and CLEAPSS Recipe Book. Hydrogen peroxide solution of ‘5 volume’ concentration is low hazard, but it will probably need to be prepared by dilution of a more concentrated solution which may be hazardous.

1 Only small samples of liver, potato and celery are required. These should be prepared for the lesson ready to be used by students. A disposal bin or bucket for used samples should be provided to avoid these being put down the sink.

Procedure

a Measure 25 cm3 of hydrogen peroxide solution into each of three conical flasks.

b At the same time, add a small piece of liver to the first flask, a small piece of potato to the second flask, and a small piece of celery to the third flask.

c Hold a glowing splint in the neck of each flask.

d Note the time taken before each glowing splint is re-lit by the evolved oxygen.

e Dispose of all mixtures into the bucket or bin provided.

Teaching notes

Some vegetarian students may wish to opt out of handling liver samples, and this should be respected.

Before or after the experiment, the term enzyme will need to be introduced. The term may have been met previously in biological topics, but the notion that they act as catalysts and increase the rate of reactions may be new. Similarly their nature as large protein molecules whose catalytic activity can be very specific to certain chemical reactions may be unfamiliar. The name catalase for the enzyme present in all these foodstuffs can be introduced.

To show the similarity between enzymes and chemical catalysts, the teacher may wish to demonstrate (or ask the class to perform as part of the class experiment) the catalytic decomposition of hydrogen peroxide solution by manganese(IV) oxide HARMFUL - see CLEAPSS Hazcard.

If students have not performed the glowing splint test for oxygen for some time, they may need reminding of how to do so by a quick demonstration by the teacher.

Health & Safety checked, 2016

Credits

This Practical Chemistry resource was developed by the Nuffield Foundation and the Royal Society of Chemistry.

© Nuffield Foundation and the Royal Society of Chemistry   

Page last updated October 2015