Food tests - practical

Question 1

what is used to test for starch in food

Answer 1

iodine

Question 2

equipment for starch test

Answer 2

food sample
test tube
iodine solution (0.01 mol/dm3)
pipettes

Question 3

method for starch test

Answer 3

1. put some of the food sample into a test tube
2. add a few drops of iodine solution to the food sample using a pipette
3. if starch is present, solution turns from brown to blue-black. note any colour change in a table of results

Question 4

used to test for reducing sugars in food

Answer 4

Benedict’s solution

Question 5

equipment for reducing sugars

Answer 5

food sample
test tube
benedict's solution
hot water bath
thermometer
pipettes

Question 6

method for reducing sugars

Answer 6

1. add equal volume or excess of benedict’s solution to the food sample in a test tube
2. place in a hot water bath for a few minutes
3. if reducing sugar is present, a brick red precipitate is formed. if absent, solution remains blue
   note any colour change in a table of results

Question 7

what is used to test for protein in food

Answer 7

biuret solution

Question 8

equipment for protein test

Answer 8

test tube
10cm3 measuring cylinder
biuret solution

Question 9

method to test for protein

Answer 9

1. add a few drops of biuret’s reagent (sodium hydroxide and copper (II) sulphate) to the food sample in a test tube
2. shake the solution to mix and wait for a a few minutes
3. if protein is present, the solution turns from blue to purple

Question 10

what is used to test for lipids in food

Answer 10

ethanol

Question 11

equipment for lipid testing

Answer 11

food sample
test tube
ethanol
distilled water

Question 12

method for lipid testing

Answer 12

1. add a few cm3 of ethanol to the food sample
2. pour this mixture into a test tube of equal volumes of distilled water
3. if lipids are present, a white emulsion is formed on the surface of the mixture
4. this is called the emulsion test

Question 13

sources of error in these tests

Answer 13

colour change of benedict’s test and biuret test may be subtle and difficult to judge if the concentration of the tested molecule is low

Question 14

safety precaution for benedict’s test

Answer 14

tie hair back and wear safety goggles when using a bunsen burner and hot water bath

Question 15

safety precaution for biuret test

Answer 15

contains copper sulphate which is poisonous and sodium hydroxide is corrosive

wash immediately if it comes into contact with skin and wipe any spills to surfaces

Question 16

safety precaution for enthanol

Answer 16

keep ethanol solution away from flames as ethanol is highly flammable