Required Practical - Decay
Biology: AQA GCSE Higher, topic 7.2.15
Practical - Temperature & Milk Decay
Investigate the effect of temperature on the rate of decay of fresh milk by measuring pH change.
Outline
- The effect of temperature on the rate of decay can be observed using milk.
- As milk takes a long time to decay, lipase and sodium carbonate are added to speed up the decay.
- As milk decays, its pH reduces. This can be observed with an indicator called Cresol red.
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Method
- Use a water bath to heat all of the components to a given temperature.
- Mix the milk, sodium carbonate and Cresol red. The resulting solution should be purple.
- Add lipase to the solution and start timing.
- When the solution turns yellow, stop timing.
- Repeat using different temperatures.
Independent and dependent variable
- The independent variable is the temperature.
- The dependent variable is the time taken for the solution to turn yellow.
Test yourself on Required Practical - Decay
What is the independent variable in an experiment investigating the effect of temperature on the rate of decay of fresh milk by measuring pH change?
Which substances can be added to speed up the decay of milk?
What is the name of the indicator used to detect the changing pH of milk?
What piece of equipment is used to heat the milk mixture to a set temperature in this experiment?
Why does the solution change colour from purple to yellow during this experiment?