Required Practical Activity 4 - Use qualitative reagents to test for a range of carbohydrates, lipids, and proteins

Question 1

What is the apparatus needed to use qualitative reagents to test for a range of carbohydrates, lipids, and proteins?

Answer 1

• Food: potato, carrot, crisps, biscuits, cheese
• Spotting tile
• Pipette
• 10cm3 measuring cylinder or plastic syringe
• Beaker
• Boiling tubes
• Heating equipment
• Test tubes
• Iodine solution
• Benedict’s reagent
• Ethanol

Question 2

What is the method used to test for starch?

Answer 2

1. Put a small piece of the food to test on a white tile.
2. Add two drops of iodine solution to the food.
3. If the iodine goes from orange-brown to blue-black, the food contains starch.

Question 3

What is the method used to test for glucose?

Answer 3

1. Mix a small sample of the food with 3 cm3 of Benedict’s solution in a boiling tube.
2. Heat the mixture in a hot water bath for 3 minutes.
3. If the solution goes from blue to brick red colour, the food contains sugar.

Question 4

What is the method used to test for protein?

Answer 4

1. Mix a small sample of the food with 3 cm³ of biuret solution.
2. Leave for 2 minutes.
3. If the mixture goes from blue to a pale purple colour, the food contains protein.

Question 5

What is the method used to test for lipids?

Answer 5

1. Mix a small sample of the food with 1 cm of ethanol in a dry test tube.
2. Pour the ethanol into a test tube full of cold water.
3. If the water goes from colourless to milky white, the food contains lipid.

Question 6

What is the colour change for positive starch test?

Answer 6

Orange/brown - blue/black

Question 7

What is the colour change for positive glucose test?

Answer 7

Blue to brick red

Question 8

What is the colour change for positive protein test?

Answer 8

Blue to lilac/purple

Question 9

What is the colour change for a positive lipid test?

Answer 9

Colourless - cloudy white precipitate