Practical: Investigating the effect of pH on the enzyme amylase Flashcards
Describe how to investigate the effect of pH on the enzyme amylase
1) Place one drop of iodine solution into each well of a spotting tile
2) Take 3 test tubes. Add 2cm^3 of starch solution in one test tube. Add 2cm^3 of amylase solution in another test tube. Add 2cm^3 of a buffer solution with a pH of 5.
3) Place all three test tubes in a water bath at 30 degrees celcius. Leave them for 10 minutes to allow the solutions to reach the correct temperature
4) Combine the three solutions into one test tube and mix with a stirring rod. Return the test tube to the water bath and start a stopwatch
5) After 30 seconds, use the stirring rod to transfer one drop of solution to a well in the spotting tile which contains iodine.
6) The iodine should turn blue-black showing that starch is present.
Continue to take sample every 30 seconds until the iodine remains orange.
7) When the iodine remains orange, this shows that the starch is no longer present (meaning the reaction has completed). Record the time for this in a results table
8) Repeat the entire experiment several times using different pH buffers (for example, pH 6, 7 and 8) to see how pH affects the time taken for the starch to be broken down
9) Control any variables such as concentration and volume of the amylase and starch solution) and keep the temperature of these solutions the same by using a water bath
What are buffer solution used for
The buffer solution is used to control the pH of a solution
Problems with the experiment
What are the solutions
Samples are only being taken every thirty seconds. This means the time recorded for the reaction to complete is approximate.
Solution: This could be addressed by taking samples every ten seconds.
Problem: The time when the iodine does not go blue-black is not always obvious
This is because the colour change tends to be gradual. Some wells might have a small amount of blue-black mixed with orange, so it can be difficult to see when the reaction has finished.
Solution: Ask several people to look at the spotting tile and decide when the reaction has completed.
How to calculate the rate of reaction after an experiment
Rate = 1000/time
How to calculate the rate of reaction if an experiment has measured how much something has changed over time
E.g.
The enzyme catalase catalyses the breakdown of hydrogen peroxide into water and oxygen. During an investigation into the activity of catalyse, 24cm^3 of oxygen was released in 50 Seconds (s). Calculate the rate of the reaction. Write you answer in cm^3s^-1 (cm^3/s)
rate of reation = the amount it has changed / time taken
e.g.
amount of product formed = change = 24cm^3
rate of reaction = change / time
= 24cm^3 / 50s = 0.48cm^3s^-1 (o.48cm^3/s)
