Food Tests

Question 1

What do you use to see if there’s starch?
What’s the method?
What’s the results?

Answer 1

Iodine test
Add several drops of iodine solution to solid food or liquid
It turns yellow/brown to blue/black

Question 2

What do you use to see if there’s sugar?
What’s the method?
What’s the results?

Answer 2

1. Benedict’s test
2. Dissolve food in 1cm3 of water using a pestle and mortar
   Add to a boiling tube
   Add 2cm3 of Benedicts solution
   Place in a boiling water bath for 2 to 3 minutes.
3. Turns from blue to green to brick red

Question 3

What do you use to see if there’s protein?
What’s the method?
What’s the results?

Answer 3

Biuret test

Dissolve food in 1cm3 of water using a pestle and mortar
Add to a boiling tube
Add 1cm3 of dilute sodium hydroxide and copper sulphate
Shake gently

Starts a pale blue and turns to lilac/purple/violet

Question 4

What do you use to see if there’s fat?
What’s the method?
What’s the results?

Answer 4

Emulsion test (ethanol)

Cut food into very small pieces
Place in a boiling tube
Add 3cm3 ethanol
Shake and leave to settle
Half fill a 2nd test tube with water
Carefully add drops of the solution from the 1st test tube to the water.

Water will have a white emulsion ring at the top of the test tube.
Turns from colourless to cloudy/milky

Question 5

How many kilojoules does 1 gram of protein give you

Answer 5

17 kilojoules

Question 6

How many kilojoules does 1 gram of fat give you

Answer 6

38 kilojoules

Question 7

How many kilojoules does 1 gram of carbohydrates give you

Answer 7

17 kilojoules

Question 8

What is the equation for energy in food

Answer 8

Energy in 1 gram of food= rise in temperature X volume of water X 4.2

Question 9

What type of foods would have more energy in them

Answer 9

Foods that are high in fat

Question 10

What are the steps in the experiment to find out how much energy is in food?

Answer 10

1. Measure 20 ml of water into a boiling tube
2. Clamp the boiling tube to a stand and stir the water with the thermometer and take it’s temperature
3. Weigh 1gram of the food
4. Place the food into a wire basket held underneath the boiling tube
5. Roast the food in a Bunsen flame until it starts to burn
6. Turn off the Bunsen
7. As the food burns the water will heat up
8. Once the food has stopped burning , stir the water and record the temperature

Question 11

How many kilojoules of energy does an average man need each day?

Answer 11

10,470 kJ per day

Question 12

How many kilojoules does an average woman need each day?

Answer 12

8370 kJ per day