Required practical 10 - Decay

Question 1

Describe how you would investigate the effect of temperature on the rate of decay of milk

Answer 1

• Place full-fat milk and create red indicator in a test tube, and lipase solution in another. Place both test tubes in a water bath and allow the temperature to equilibrate.
• Transfer drops of lipase into the other test tube and start stop watch. Stir until solution turns yellow and record the time taken.
• Repeat at different temperature and plot graph of temperature (x) against time taken (y).

Question 2

Why does the addition of lipase accelerate the decay of milk?

Answer 2

Lipase is an enzymes which catalyses the breakdown of lipid to fatty acids and glycerol. It provides an alternative reaction route with lower activation energy.

Question 3

Why does pH of the solution change during this reaction?

Answer 3

Fat in milk is broken down into fatty acids by the enzyme lipase, lowering the pH.

Question 4

What color is cresol red in alkaline and acidic solutions?

Answer 4

Alkaline: purple.
Acid: yellow.

Question 5

Why does an increase in temperature increase the rate of this reaction?

Answer 5

Enzymes and reacting particles have a higher kinetic energy and collide more frequently, leading to a faster rate of reaction.

Question 6

Why might the rate of reaction decrease if the temperature if very high?

Answer 6

Enzymes become denatured as active site changes shape - cannot catalyse reaction.