3.20 Food Tests (Practical)

Question 1

How do you prepare a food sample?

Answer 1

• Break it up with a mortar and pestle
• Put the crushed food in a beaker of distilled water
• Stir it with a glass rod until some of it dissolves
• Filter out the solution with a funnel that’s been lined with filter paper

Question 2

How do you carry out the Benedict’s test? (3)

Answer 2

• Prepare the food sample and transfer 5cm cubed of it into a test tube. You also need to prepare a water bath and set it to 75 degrees celsius
• Once your water bath is ready, you can add about 10 drops of benedict solution to the test tube and place it in the water bath for 5 minutes.
• For safety reasons, use a test tube holder when you do this and point the tube away from you and anybody else

Question 3

What colour will the solution go if reducing sugars are present?

Answer 3

Blue, yellow or brick red depending on the concentration

Question 4

How do you carry out the iodine test? (3)

Answer 4

• Take 5cm cubed of your food sample and add a few drops of iodine solution
• This will turn your solution into a brown colour
• Shake the test tube gently

Question 5

What colour does the food sample in the iodine test turn if starch is present?

Answer 5

Blue-black

Question 6

How do you carry out the Biuret test? (2)

Answer 6

• You put 2cm cubed of the food sample into the test tube
• Add a few drops of sodium hydroxide solution to make the solution alkaline
• Then, add some copper (II) sulfate solution (which is bright blue)

Question 7

What colour does the food sample turn in the Biuret test if it does contain proteins?

Answer 7

Pink/purple

Question 8

How do you carry out the emulsion test? (2)

Answer 8

• Put your food sample in the test tube and add 2cm cubed of ethanol into it
• Shake vigorously then add 2cm cubed of distilled water

Question 9

How will the food sample look in the emulsion test if lipids are present?

Answer 9

It will go a cloudy white colour

Question 10

Which test is used to detect the presence of reducing sugars? (i.e. small sugars like glucose)

Answer 10

Benedict’s test

Question 11

What does iodine test for?

Answer 11

Starch

Question 12

Which test is used to detect the presence of proteins?

Answer 12

Biuret test

Question 13

What colour will the food sample be in the Biuret test if there are no proteins present?

Answer 13

Blue

Question 14

Which test is used to test for the presence of lipids?

Answer 14

Emulsion test