Required Practical: Decay Flashcards

All 5 cards in this deck

What are the steps of the required practical on the effect of temperature on the rate of decay of milk?

e.g. testing 5 °C, 15 °C and 25 °C

1. Put the same volume of the same fresh milk into each container, e.g. $25\ \text{cm}^3$.
2. Keep each at a different constant temperature in a water bath, e.g. 5 °C, 15 °C, 25 °C.
3. Measure and record the pH at regular intervals (e.g. each day) until it reaches a set pH.

Give two control variables for the investigation into the effect of temperature on the decay of milk.

Volume of milk and type/freshness of the milk (also exposure to air and the time of day the pH is measured).

Give one way the pH of decaying milk can be measured.

Universal indicator paper or solution, or a pH meter (pH probe).

How can milk be kept at a constant temperature during the decay practical?

Place the container in a water bath (or an incubator) set to that temperature.

What are the steps to calculate the rate of pH change of decaying milk?

e.g. pH falls from 6.6 to 5.6 in 2 days

1. Find the change in pH: $6.6 - 5.6 = 1.0$.
2. Divide by the time taken: $1.0 \div 2$.
3. Rate $= 0.5$ pH units per day.