Milk Decay GCSE Biology Practical
Investigate the effect of temperature on the rate of decay of milk by measuring pH change.
In this required practical, students are to investigate the effect of temperature on the rate of decay of milk. The experiment uses a colour changing indicator to identify the end point of the reaction. Temperature is varied using a water bath so the students handling of laboratory equipment is also put to the test
Equipment (per pair of participants)
• Safety glasses
• Bunsen burner
• 250ml beaker
• 100ml beakers
• 7 x boiling tubes
• Boiling tube rack
• Chinagraph pencil or permanent pen
• 10ml syringes
• Thermometer
• Stopwatch
• Cresol Red indicator in dropping
bottles
• Kettle
• Lipase solution (5%)
• Anhydrous Sodium Carbonate solution
(0.05M)
• CLEAPSS Hazcards: 32, 33, 95A
Investigating the Effect of Temperature on Lipase Activity
Method
Preparation
- Safety First
- Put on safety glasses to ensure proper eye protection throughout the experiment.
- Label and Prepare Tubes
- Label two boiling tubes: ‘Lipase’ and ‘Milk’.
- Add the following to each tube:
- ‘Lipase’ tube: 5ml of Lipase solution.
- ‘Milk’ tube: 5ml of milk, 5 drops of Cresol Red indicator, and 7ml of sodium carbonate solution (resulting in a purple/pink colour).
- Insert Thermometer
- Place a thermometer into the ‘Milk’ tube to monitor the temperature during the experiment.
Water Bath Setup
- Prepare the Water Bath
- Set up a 250ml beaker as a water bath and use a Bunsen burner to heat the water until it reaches your desired temperature.
- Monitor the water bath temperature carefully and adjust the flame to maintain consistency.
- Temperature Equilibration
- Place both the ‘Lipase’ and ‘Milk’ tubes into the water bath.
- Wait until the thermometer in the ‘Milk’ tube reads the desired temperature.
Experimental Procedure
- Start the Reaction
- Using a fresh dropping pipette, add 1ml of Lipase from the ‘Lipase’ tube into the ‘Milk’ tube.
- Start the stopwatch immediately.
- Monitor the Reaction
- Stir the contents of the ‘Milk’ tube using the thermometer while observing the colour change.
- Stop the stopwatch as soon as the solution turns yellow.
- Record Results
- Note the time taken (in seconds) for the solution to turn yellow in a suitable results table.
Repeat for Different Temperatures
- Adjust the water bath temperature for the next trial, ensuring the temperature differs by at least 5°C for each new experiment.
- Repeat the procedure for a minimum of five different temperatures, following the same steps for each trial.
Video produced by @revisechemistrywithmrb practical GCSE Chemistry tutorials by a specialist Chemistry teacher with over 25 years experience teaching Chemistry and Biology.
Technician tips
The milk used must be fresh, full fat/whole milk (source locally).
- The Sodium Carbonate used to make the solution must be made from the Anhydrous salt. 5.2g/L of the salt gives a 0.05mol solution.
- All reagents, including the milk, should be at room temperature at the start of the experiment.
- The practical uses 5% Lipase Solution. One 25g pot of Lipase is used to make 500mls of 5% solution. Lipase is quite dicult to dissolve. We would recommend giving plenty of time for the Lipase to dissolve as much as possible before the lesson using an electronic magnetic stirrer.
To do this practical, you will need
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Investigate the effect of temperature on decay of milk for the GCSE Biology required practical. The experiment involves students using a colour changing indicator to identify the end point of the reaction. Shop our full range of biology equipment for this practical including safety glasses, bunsen burners, beakers and more. Discover more science equipment at Philip Harris developed by our science experts for schools and FE.
