Tests for biological molecules

Question 1

How do you test for reducing sugars and what is the positive result?

Answer 1

Add Benedict’s

Blue -> Brick red

Question 2

How do you test for non-reducing sugars and what is the positive result?

Answer 2

(Negative Benedict’s must be first seen)
Hydrolyse by heating with hydrochloric acid, then neutralise with sodium hydrogen carbonate
Then perform another Benedict’s
Blue -> Brick red

Question 3

How do you test for starch and what is the positive result?

Answer 3

Add iodine solution

Colour change to blue-black

Question 4

How do you test for lipids and what is the positive result?

Answer 4

Add ethanol to the sample, shake, then pour the mixture into water
White emulsion appears

Question 5

How do you test for proteins and what is the positive result?

Answer 5

Add biuret reagent

Violet colour appears

Question 6

What is the intensity of colour proportional to in biuret test?

Answer 6

The higher the number of peptide bonds, the more intense the colour