Required Practical 10 - Decay

What is lipase?

An enzyme that catalyses the breakdown of lipids into fatty acids and glycerol.

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

Lipase catalyses the breakdown of lipids in milk, providing an alternative reaction route with a lower activation energy.

What happens to the pH of the solution during the decay of milk?

The pH decreases as lipase breaks down fats into fatty acids, making the solution more acidic.
What colour is cresol red in alkaline and acidic solutions?

How would you investigate the effect of temperature on the rate of decay of milk?

• 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 milk solution and start the stopwatch.

• Stir until the solution turns yellow and record the time taken.

• Repeat at different temperatures and plot a graph of temperature (x) against time taken (y).

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

Higher temperatures increase the kinetic energy of enzymes and reacting particles, leading to more frequent collisions and a faster rate of reaction.

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

Enzymes can become denatured at high temperatures, causing the active site to change shape and preventing the enzyme from catalysing the reaction.