2. Organisation (required practical 4 - food tests)

Question 1

What is required practical 4?

Answer 1

Food tests

Question 2

Why must safety goggles be worn during the practical?

Answer 2

All of the chemicals in the test are potentially hazardous

Question 3

What are the steps for the practical for starch? (6)

Answer 3

1. Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste
2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water
3. Filter the solution to remove suspended food particles
4. Place 2cm3 of our food solution into a test tube
5. Then add a few drops of iodine solution, which is an orange colour
6. If starch is present, than the iodine solution will turn blue-black. If no starch is present, then the iodine solution will stay orange

Question 4

What are the steps for the practical for sugar, such as glucose? (8)

Answer 4

1. Take the food sample and grind it with distilled water using a mortar and pestle, until it makes a paste
2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water
3. Filter the solution to remove suspended food particles
4. Place 2cm3 of our food solution into a test tube
5. Add 10 drops of Benedict’s solution, which is a blue colour
6. Place the test tube containing our solution into a beaker, and half-fill the beaker with hot water from a kettle
7. Leave this for 5 minutes. If sugars are present, then the Benedict’s solution will change colour
8. The colour of the Benedict’s solution gives an approximate idea of the amount of sugar present

Question 5

What can the benedict’s solution not do?

Answer 5

tell us the exact amount of sugar present

Question 6

What does a green colour change of a Benedict’s solution tell us?

Answer 6

That there is a small amount of sugar

Question 7

What does a yellow colour change of a Benedict’s solution tell us?

Answer 7

that there is more sugar present

Question 8

What does a brick-red colour change of a Benedict’s solution tell us?

Answer 8

that there is a lot of sugar present

Question 9

What are reducing sugars?

Answer 9

Sugars, like glucose, that work for the Benedict’s test

Question 10

What are the steps for the practical for proteins? (6)

Answer 10

1. Take the food sample and grind this with distilled water using a mortar and pestle, until you make a paste
2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water
3. Filter the solution to remove suspended food particles
4. Place 2cm3 of our food solution into a test tube
5. Add 2cm3 of Biuret solution, which is a blue colour
6. If protein is present then the Biuret solution will change from blue to a purple or lilac colour

Question 11

What are the steps for the practical for lipids? (5)

Answer 11

1. Take the food sample and grind this with distilled water using a mortar and pestle, until you make a paste
2. Transfer 2cm3 of our food solution into a test tube
3. Add a few drops of distilled water and ethanol
4. Gently shake the solution
5. If lipids are present, then a white cloudy emulsion forms

Question 12

Why do we not filter the solution when testing for lipids?

Answer 12

Because lipid molecules can stick to filter paper

Question 13

Why is it very important that no naked flames are present during the lipids food test experiment?

Answer 13

Because ethanol is highly flammable