1. Topic
Food tests
Level
GCSE (or any course for students aged 11-16)
Outcomes
Carry out a tests for sugar, protein and lipid using Benedict's solution, Biuret reagent and ethanol.
Create a results table for a qualitative investigation involving colour changes
Information for teachers
This activity should be done once students have a secure understanding of how to perform each food test listed above. The simple context of urine tests helps students to understand the rationale behind wanting to test for different food groups. Once students have been introduced to the challenge, ask them to create a results table. This will focus their plan of what to do during the experiment. Only when students have completed a suitable table can they carry out the experiment.
I have not specified here how to make up the different ‘urine samples’ but just use materials available in your school. Obviously, these are pretend solutions containing a mixture of water, yellow dye and the necessary food – glucose, protein or lipid. Make sure the solutions give an obvious positive result. For information on the reagents see CLEAPSS. Please make sure you have conducted your own risk assessment before carrying out this experiment.
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2. A B C Introducing the problem you will investigate
You have been given three beakers of ‘urine’ from three different patients to test. One patient is diabetic, one patient has high blood pressure and one patient has lipiduria. Use the key information below, together with your knowledge of food tests, to find out which sample belonged to which patient. Start by drawing a results table. A B C
Key information:
High blood pressure can cause protein from the blood to be forced through filters in the kidney causing protein to be present in the urine.
Sugar (glucose) normally is not found in urine. But when blood sugar levels rise well above normal the kidneys may release some of the excess sugar from the blood into the urine
Lipiduria is the presence of lipids in the urine. It is a symptom of kidney damage.

3. Colour with Benedict's solution Colour with Biuret reagent
Results table
Urine sample
Colour with Benedict's solution
Colour with Biuret reagent
Cloudy layer produced with ethanol?
Possible Disease (diabetes, high blood pressure, lipiduria) A B C
Questions to complete
Complete your results table during the experiment
Use your results to identify which sample (A-C) belonged to which patient: diabetic, patient with high blood pressure, patient with lipiduria. Complete the table.
The urine from each patient was tested with iodine. The results from each test were negative i.e. the iodine solution remained brown. What conclusion can you make?
Thinking further about food tests
John says that burgers are fat. Why is this statement not fully correct.
Humans eat food containing starch. So why is starch not found in human blood.
Benedict's solution contains copper (II) ions which are soluble. What happens to these copper ions when they react with glucose?