2.6 Required practical: food tests
6 exam questions worth 12 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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Which reagent is used to test for protein?
Choose one answer.
Correct Not quite: the answer is Biuret reagent
Mark scheme
C: biuret reagent
Model answer
C: biuret reagent. It turns from blue to purple if protein is present.
Describe how to use Benedict's solution to test a food for reducing sugars. Give the positive result.
Mark scheme
- add Benedict's solution to the food sample (1)
- heat in a water bath / at about 75 °C (for about 5 minutes) (1)
- (blue) turns brick-red / orange / green / yellow if sugar is present (1)
Model answer
Add Benedict's solution to the food solution and heat it in a water bath at about 75 °C for 5 minutes. If a reducing sugar is present the colour changes from blue to green, yellow or brick-red.
A student tested a food. The results were:
- iodine: stayed orange-brown
- biuret: turned purple
- Sudan III: red layer on top
Which food molecules does the food contain?
Mark scheme
- protein (1)
- lipid / fat (1)
- do not accept starch
Model answer
The food contains protein and lipid, but no starch.
Before testing, the food is ground with distilled water and filtered.
Give one reason for each step.
Mark scheme
- grinding: to break up the food / so the molecules dissolve / mix with water (1)
- filtering: to remove solid pieces / so the colour can be seen clearly (1)
Model answer
Grinding breaks the food up so the food molecules dissolve in the water. Filtering removes solid pieces, so the colour change is easy to see.
Four drinks were tested with Benedict's solution. The colours were: A green, B blue, C brick-red, D yellow.
List the drinks in order from the most to the least reducing sugar.
Mark scheme
- C, D, A, B (2)
- allow 1 mark for one pair in the wrong order
Model answer
C, D, A, B. Brick-red shows the most sugar and blue shows none.
Give a safety precaution for the ethanol emulsion test and explain why it is needed.
Mark scheme
- keep away from flames / no Bunsen burners nearby (1)
- because ethanol is flammable (1)
Model answer
Keep the ethanol away from any flames, because ethanol is flammable.
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