B2: Quiz 6 – Answers
- Get a sample of the food and break it up using a pestle and mortar.
- Put the ground up food in a beaker and add some distilled water (pure water).
- Mix the distilled water and ground up food to create a solution.
- Filter the solution to get rid of any solid bits of food
2) We add a few drops of iodine to our test tube containing our food sample. Iodine is brown/ orange. When starch is present, the iodine will react with the starch resulting in the solution becoming blue/ black. If no starch is present, the solution will remain brown/ orange
3)
a) We transfer about 5 cm3 of our food sample into a test tube. We then add a few drops of Sudan III into the test tube and gentle shake. If lipids are present, a red layer will form on the top of the sample. If no lipids are present, no red layer will form on the top of the sample.
b) No – we do not filter our sample
4) We test for proteins by using the biuret test. We transfer a small sample of the food (around 2 cm3) to a test tube. We then add 2 cm3 of Biuret solution and shake the test tube. Biuret solution is a blue solution. If proteins are present in our sample, the solution will change from blue to pink or purple. If no proteins are present in the sample, the solution will remain blue.
5)
a) The steps are:
> Add 5 cm3 of our food sample to a test tube.
> Use a water bath to heat the test tube up to 75°C.
> Add about 10 drops of Benedict’s solution so that the solution becomes blue.
> Leave the test tube in the water bath for around 5 minutes. Make sure that the test tube is facing away from you when it is left in the water bath (for safety reasons).
> Observe the colour change
b) Blue
c) C, D, A, B
1) The process for preparing our food samples is pretty much the same for all of the different food tests that you need to know for this GCSE. Outline this general process.
For the following questions, you do not have to discuss how to prepare the sample of food that we are testing.
2) Describe the test for starch.
3)
a) Describe the test for lipids.
b) When we are preparing our food sample for the testing of lipids, do we filter it to get rid of any solid bits?
4) Describe the test for proteins.
5) We can test for the presence of reducing sugars by using Benedict’s test.
a) Outline the steps that we undertake for Benedict’s test.
b) What colour will the test tube with our food sample and Benedict’s solution be if the food sample does not contain any reducing sugars?
A teacher gives a student 4 different solutions that contain different concentrations of reducing sugars. The student undertakes Benedict’s test on the four different solutions and the colours of the tests tubes after she does Benedict’s test are shown in the table below.