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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?