Biology Required Practical: Decay of Milk

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Investigating the effect of temperature on the rate of decay of fresh milk by measuring pH change.

Set up a water bath by half filling one of the 250 cm³ beakers with hot water from the kettle.
Label two test tubes: one ‘lipase’ and the other ‘milk’.
In the first test tube put 5 cm³ of lipase solution.
In the other test tube put five drops of phenolphthalein solution.
Use a calibrated dropping pipette to add 5 cm³ of milk to the tube containing the phenolphthalein.
Use another pipette to add 7 cm³ of sodium carbonate solution to this test tube. The solution should be pink.
Put a thermometer into this test tube.
Put both test tubes into the water bath and wait until the contents reach the same temperature as the water bath.
Use another dropping pipette to transfer 1 cm3 of lipase into the tube containing the milk and phenolphthalein. Immediately start timing.
Stir the contents of the test tube until the solution loses its pink colour.
Record the time taken for the pink colour to disappear.
Repeat the above steps for different temperatures of water bath. You can obtain temperatures below room temperature by using ice in the beaker instead of hot water.
Record your results in a table and plot a graph of your results

Decay - GCSE Biology Required Practical
How to model decay using milk, lipase and phenolphthalein and observe how temperature affects its rate?

Required Practical: Decay
Describe how to investigate the effect of temperature on the rate of decay of fresh milk by measuring the pH change.

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