Download 41. Testing for enzymes

Classic chemistry experiments
41.
103
Testing for enzymes
Topic
Catalysis, rates of reaction, enzymes.
Timing
30 mins.
Description
Students use the enzymes in liver, potato and celery to catalyse the production of water
and oxygen from hydrogen peroxide.
Apparatus and equipment (per group)
3
▼ 100 cm Conical flask
3
▼ 25 cm Measuring cylinder.
Chemicals (per group)
▼ Hydrogen peroxide solution (5 volume)
▼ Liver (small piece)
▼ Potato (small piece)
▼ Celery (small piece).
Teaching tips
It may be useful to discuss how to decide which reaction is fastest. Teachers should be
sensitive to the needs of vegetarian students. Manganese dioxide, copper oxide and
calcium carbonate can also be tested as catalysts to illustrate biological and chemical
catalysts. Cooked liver (well done) can also be used. This will not work as well,
illustrating the fact that enzymes can be denatured.
A temperature sensor or a pressure sensor attached to a computer can be used to
monitor the progress of this reaction. The technique can be used to provide a more
graphic demonstration or indeed as the basis for an investigation into rates of reactions.
Background theory
Students should understand the concept of an enzyme as a biological catalyst.
Safety
Wear eye protection. Provide a bucket to collect discarded liver, do not allow it to
collect in sinks.
Answers
1. Oxygen is produced.
2. It can relight a glowing splint.
3. The liver.
4. Hydrogen peroxide → oxygen + water
5. Rate of mass loss. Use a gas syringe, amount of fizz, or any other suitable method.
Classic chemistry experiments
41
Testing for enzymes
Introduction
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.
Glowing splint
Conical flask
Hydrogen peroxide solution
Liver
What to record
What do you see? What gas is produced, and which enzyme source makes the most
effective catalyst?
What to do
3
1. Using a measuring cylinder, put 25 cm of hydrogen peroxide solution into a
conical flask.
2. Add a small piece of liver.
3. Test the gas given off with a glowing splint.
3
4. Dispose of this mixture, including the liver, into a bucket, and put another 25 cm
of hydrogen peroxide solution in the flask.
5. Add a small piece of potato.
6. Test the gas given off with a glowing splint.
7. Repeat this experiment with a piece of celery instead of potato.
Safety
Wear eye protection.
Questions
1. Which gas is produced in this reaction?
2. What is the test for this gas?
3. Which enzyme source produces the fastest reaction (liver, potato or celery)?
4. Write a word equation for this reaction.
5. How could the rate of gas production be measured?