This practical allows you to:
* discover how pH affects the rate of an enzyme controlled reaction * evaluate the experimental procedure
Follow your teacher’s instructions for handling the solutions. Wear eye protection when handling the iodine solution.
* Place single drops of iodine solution in rows on the tile. * Label a test tube with the pH to be tested.
* Use the syringe to place 2 cm3 of amylase into the test tube. * Add 1 cm3 of buffer solution to the test tube using a syringe. * Use another syringe to add 2 cm3 of starch to the amylase/ buffer solution. Start the stop clock and leave it on throughout the test. Mix using a plastic pipette. * After 10 seconds, use the plastic pipette to place one drop of the mixture on the first drop of iodine. The iodine solution should turn blue-black. Squirt the rest of the solution in the pipette back into the test tube. * Wait another 10 seconds. Then remove a second drop of the mixture to add to the next drop of iodine. * Repeat step g until the iodine solution and the amylase/ buffer/ starch mixture remain orange. * You could prepare a control drop for comparison with the test drops. What should this contain? * Count up how many iodine drops you have used, each one equals 10 seconds of reaction time. * Repeat the whole procedure with another of the pH buffers or pool your results with others in your class. * Collect repeat data if there is time.
* Plot a graph of time taken for starch to break down against pH. OR
Calculate the rate of the reaction by calculating 1 ÷ time. Plot rate of reaction against pH.
1 It is important to add the buffer to the enzyme before adding the starch. Why is this?
2 How does a control help you with the colour comparison?
3 Are there any anomalies or inconsistencies in your results?
4 Do you think your results...