Try this class experiment to detect the presence of enzymes as they catalyse the decomposition of hydrogen peroxide
Enzymes are biological catalysts which increase the speed of a chemical reaction. They are large protein molecules and are very specific to certain reactions. Hydrogen peroxide decomposes slowly in light to produce oxygen and water. The enzyme catalase can speed up (catalyse) this reaction.
In this practical, students investigate the presence of enzymes in liver, potato and celery by detecting the oxygen gas produced when hydrogen peroxide decomposes. The experiment should take no more than 20–30 minutes.
- Eye protection
- Conical flasks, 100 cm3, x3
- Measuring cylinder, 25 cm3
- Bunsen burner
- Wooden splint
- A bucket or bin for disposal of waste materials
- Hydrogen peroxide solution, ‘5 volume’
- Small pieces of the following (see note 4):
Health, safety and technical notes
- Read our standard health and safety guidance.
- Wear eye protection throughout. 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 HC050 and CLEAPSS Recipe Book RB045. 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.
- 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.
- Measure 25 cm3 of hydrogen peroxide solution into each of three conical flasks.
- 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.
- Hold a glowing splint in the neck of each flask.
- Note the time taken before each glowing splint is relit by the evolved oxygen.
- Dispose of all mixtures into the bucket or bin provided.
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 HC060).
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.