[bio] food tests

Question 1

biuret’s test test for what?

Answer 1

test for the presence of proteins

Question 2

iodine test test for what?

Answer 2

test for the presence of starch

Question 3

benedict’s test test for what?

Answer 3

test for presence of reducing sugar

Question 4

ethanol emulsion test test for what?

Answer 4

test for the presence of fats

Question 5

steps for iodine test

Answer 5

1. place food substance on white tile (solid foods need to chop up to smaller pieces)
2. add 2-3 drops of dilute iodine solution for substance to be tested
3. observe colour changes

Question 6

possible results for iodine test

Answer 6

blue-black colouration is observed - starch is present
solution remained brown - starch is absent

Question 7

steps for benedict’s test

Answer 7

1. add 2cm3 of benedict’s solution into 2cm3 of food solution
2. shake the mixture
3. place test tube in boiling water bath for a maximum of 5 minutes
4. observe precipitate formation and colour changes

Question 8

possible results for benedict’s test

Answer 8

solution remained blue - reducing sugar is absent
green precipitate is formed - little concentration of reducing sugar is present
yellow precipitate is formed - little concentration of reducing sugar is present
orange precipitate is formed - moderate concentration of reducing sugar is present
brick red precipitate is formed - huge concentration of reducing sugar is present

Question 9

steps for ethanol emulsion test

Answer 9

1. for solid food mixture, chop solid food into small pieces then put in a dry test tube
2. add 2cm3 of ethanol into 2cm3 of food solution
3. shake the mixture thoroughly
4. decant the ethanol mixture into another test tube containing 2cm3 of water

Question 10

possible results for ethanol emulsion test

Answer 10

a white emulsion was formed - fats is present
solution remained colourless - fats is absent

Question 11

steps for biuret’s test

Answer 11

1. add 1cm3 of sodium hydroxide into 2cm3 of food solution
2. shake thoroughly
3. add 1% copper (ii) sulfate solution drop by drop, shaking after each drop and observe for colour change

Question 12

possible results for biuret’s test

Answer 12

violet colouration is observed - protein is present
solution remained blue - protein is absent

Question 13

how to draw the table for observations

Answer 13

sample food test observations conclusions