Testing For Biological Molecules

Question 1

Reducing sugar

Answer 1

1) add equal measures of Benedict’s solution
2) place in water bath at 95°C for 5 mins
3) if present, red/brown precipitate. If not, blue

Question 2

Non reducing sugar

Answer 2

1) add dilute acid (HCl)
2) water bath, 95°C, 5 mins
3) neutralise with alkali (sodium hydrogencarbonate)
4) add Benedict’s solution
5) bath 95°C for 5 mins
6) if present, red/brown precipitate. If not, pale blue

Question 3

Protein

Answer 3

Biuret Test

1) add sodium hydroxide
2) add copper sulphate
3) if present, lilac. If not, pale blue

Question 4

Lipid

Answer 4

Emulsion Test

1) mix with ethanol
2) add water
3) if present, milky/cloudy colour. If not, clear

Question 5

Starch

Answer 5

1) add iodine solution drop by drop

2) if present, dark blue. If not, pale yellow