The fat in milk is broken down by the enzyme lipase.
A group of students investigate the effect of temperature on this breakdown of fat.
In their investigation they use an indicator called phenolphthalein.
Phenolphthalein is pink in alkali conditions but colourless in pH values below 8.
Step 1 | One student puts 5 drops of phenolphthalein and 5 ml of full fat milk into a test tube. |
Step 2 | She adds 1 ml of lipase and stirs the mixture. |
Step 3 | She measures the time for the pink indicator colour to disappear. |
The other students repeat these three steps but at different temperatures.
Table 16.1 shows the results of the group.
Temperature (°C) |
Time for pink colour to disappear (s) |
20 | 480 |
40 | 240 |
60 | 270 |
80 | 960 |
Table 16.1
The pH falls as the fat in milk breaks down.
Explain why.
Plot a graph of the results from Table 16.1 and draw a line of best fit.
Explain why the results at 20 °C and 40 °C are different.
Explain why the results at 40 °C and 80 °C are different.
The teacher says that she cannot say for certain that it is 40°C.
[1]
The students rounded each time they measured to the nearest 10 seconds.
They rounded the times because they found it difficult to judge exactly when the pink colour had disappeared.
Describe and explain two ways the method could be improved to give a more accurate measurement.
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