Decay Practical

Question 1

How the practical works

Answer 1

• When food decays microorganism release enzymes onto them
• You can observe the action of the enzyme lipase on a sample of milk made alkaline
• Its pH will become more acidic with the production of fatty acids

Question 2

IV

Answer 2

• Temperature
• Changed using a water bath

Question 3

DV

Answer 3

• Time taken for pH to change colour

Question 4

CV

Answer 4

• Volume/concentration of milk
• concentration of lipase

Question 5

Hazard

Answer 5

Chemicals (lipase, sodium carbonate indicator)

Question 6

Risk

Answer 6

• Chemicals are irritants
• May damage skin and eyes

Question 7

Safety

Answer 7

Wear eye protection

Question 8

Method

Answer 8

• Add lipase to a test tube and place in a water bath at 20C
• In another test tube add milk and 5 drops of Cresol Red solution and sodium carbonate
• Leave for 5 minutes to allow solutions to reach the same temperature
• Add the lipase to the milk and start the stopwatch immediately
• Stir the mixture continuously and stop when the solution changes to yellow. Record time
• Repeat using different temperature of water baths

Question 9

Why add Cresol Red Solution

Answer 9

indicator

Question 10

How could you make the expriment more accurate

Answer 10

You could use a pH probe which continuously measured the pH

Question 11

Results

Answer 11

• Decay relies on enzyme therefore there will be an optimum temperature
• The faster the colour change the quicker the pH decreased ( more fatty acids were produced)
• In high temperatures pH may not change as the enzyme has become denatured
• At low temperatures enzymes have less kinetic energy so work slower

Question 12

why add sodium carbonate to milk

Answer 12

to make alkaline