Food tests

Question 1

Preparation of food sample

Question 2

1

Answer 2

grind the piece of food using a pestle and mortar

Question 3

2

Answer 3

transfer the ground up food to a beaker and add some distilled water

Question 4

3

Answer 4

give the mixture a good stir with a glass rod to dissolve some of the food

Question 5

4

Answer 5

Filter the solution using a funnel lined with filter paper to get rid of the solid bits of food

Question 6

Test for sugars

Question 7

Equipment

Answer 7

. food sample
. a test tube
. Benedict solution
. pipette
. hot water bath
.thermometer

Question 8

Step 1

Answer 8

Prepare the food sample and transfer 5cm^3 to a test tube, and prepare a water bath set to 75 degrees Celsius

Question 9

Step 2

Answer 9

Add benedict solution in equal or excess to a test tube

Question 10

Step 3

Answer 10

Place the test tube in the water bath and leave it for 5 mins. use test tube holders

Question 11

Step 4

Answer 11

If the food sample contains a sugar it will change from light-blue green, yellow, orange or brick red depending on the concentration

Question 12

Possible errors

Answer 12

colour change may be subtle and difficult to judge if the concentration of the tested molecule is low

Question 13

What kind of sugars will react with Benedict solution?

Answer 13

Reducing sugars e.g. glucose

Question 14

What are the hazard?

Answer 14

. benedicts solution is an irritant
.bunsen burner or water bath can be used

Question 15

Safety measures

Answer 15

.wear safety goggles and gloves
.tie hair back
. avoid contact with skin and eyes
. using a test tube holder to make sure test tube is pointing away from you when in water bath.

Question 16

Test for starch

Answer 16

equipment:
.food sample
.test tube
.iodine solution (0.01 mol/dm^3)
.pipettes

Question 17

A

Answer 17

Make a food sample and transfer 5cm^3 into a test tube

Question 18

B

Answer 18

Using a test tube add a few drops of iodine solution and gently shake the tube to mix the contents

Question 19

C

Answer 19

If starch is present the colour of the solution will change from black to BLUE-BLACK

Question 20

Extra info

Answer 20

the starch test can also be used with a microscope to stain starch grains in plant cells.

Question 21

Hazards

Answer 21

. iodine solution is an irritant

Question 22

Precautions

Answer 22

.wear goggles and gloves
.avoid contact with skin and eyes

Question 23

Test for proteins

Answer 23

Equipment:
. test tube
.biuret solution
.10cm^3 measuring cylinder

Question 24

Step A

Answer 24

Prepare a food sample and transfer 2cm^3 to a test tube

Question 25

Step B

Answer 25

Add 2cm^3 of biuret solution (could be 2 biuret solutions) to the sample and mix by shaking it gently

Question 26

Step C

Answer 26

If the food contains protein the solution will change from blue to purple or have a purple ring if there is no protein then it will stay blue

Question 27

Possible errors

Answer 27

colour change may be subtle and difficult to judge if the concentration of the tested molecule is low

Question 28

What is biuret solution made of?

Answer 28

Sodium Hydroxide and copper (II) sulphate

Question 29

Hazards

Answer 29

Biuret solution is corrosive copper sulphate is poisonous and sodium hydroxide is corrosive

Question 30

Precautions

Answer 30

.wear safety goggles and gloves . avoid contact with skin and eyes .handle with care .wash immediately if it comes into contact with skin .wipe away any spills to surfaces

Question 31

Sudan III

Answer 31

Equipment: .pipette .food sample .test tube .water .Sudan III

Question 32

I (alif)

Answer 32

Prepare a food sample without filtration and transfer about 5cm^3 into a test tube

Question 33

ب

Answer 33

Use a pipette to add 3 drops of Sudan III stain solution to the test tube and gently shake it

Question 34

ت

Answer 34

Sudan III stains lipids . If lipids are present then the mixture will separate out into 2 layers - top will be bright red. If lipids aren't present no separate red layer will form at the top of the liquid.

Question 35

Hazard

Answer 35

.Sudan III solution is flammable cos it's dissolved in alchohol

Question 36

Precautions

Answer 36

. wear safety goggles and gloves .keep away from open flames

Question 37

Emulsion test

Answer 37

Equipment: .food sample .test tube .distilled water .ethanol

Question 38

I

Answer 38

Add 3cm^3 of ethanol and 1cm^3 of a food sample to a test tube with 3cm^3 of distilled water

Question 39

ㅍ

Answer 39

If lipids are present, a white emulsion if formed on the surface of the mixture but if there are no lipids then it will remain colourless

Question 40

Hazards

Answer 40

Ethanol is flammable

Question 41

Precautions

Answer 41

.tie hair back .wear goggles and gloves .keep away from open flames