PAG 09 - Qualitative Testing

Question 1

What is Biuret’s test for?

Answer 1

Protein.

Question 2

Outline the procedure to a Biuret test.

Answer 2

1. Add sodium hydroxide solution.
2. Add copper (II) sulphate solution. 3. If the colour changes from blue to
   purple, protein is present.

Question 3

What does iodine test for?

Answer 3

Starch

Question 4

What is the colour change for a positive iodine test?

Answer 4

Brown to blue-black.

Question 5

Outline the procedure to the emulsion test.

Answer 5

1. Add ethanol.

2. Pour solution into water. 3. A white emulsion forms.

Question 6

What does Benedict’s reagent test for?

Answer 6

Reducing sugars.

Question 7

Outline the test for reducing sugars.

Answer 7

1. Add equal volume or excess Benedict’s reagent to a sample and boil.
2. If positive, colour changes from blue to red, with a brick-red precipitate.

Question 8

Outline the test procedure for non-reducing sugars.

Answer 8

1. Add dilute HCl and boil.
2. Neutralise with sodium hydrogen
   carbonate.
3. Add Benedict’s reagent and boil.
4. If positive, colour changes from blue to
   red, with brick-red precipitate.

Question 9

What is a method to test for glucose specifically?

Answer 9

Dip the pad of a glucose test strip into the sample. Colour change will occur if glucose is present.
Concentration can be found by comparing colour to a colour standard chart.