RP10 - 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 cresol 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 stopwatch. Stir until solution turns yellow and record the time taken.
● Repeat at different temperatures 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 enzyme which catalyses the breakdown of lipid to fatty acids and glycerol. It provides an alternative reaction route with a lower activation energy

Question 3

Why does the 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 colour is cresol red in alkaline and acidic solutions?

Answer 4

Alkaline: purple

Acidic: yellow

Question 5

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

Answer 5

Enzyme 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 is very high?

Answer 6

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