Qualitative Testing: Development of Practical Skills in Biology: Biology OCR A Level

What is Biuret's test for?

Protein.

Outline the procedure to a Biuret test.

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

What does iodine test for?

Starch.

What is the colour change for a positive iodine test?

Brown to blue-black.

Outline the procedure to the emulsion test.

1. Add ethanol.
2. Pour solution into water.
3. A white emulsion forms.

What does Benedict’s reagent test for?

Reducing sugars.

Outline the test for reducing sugars.

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.

Outline the test procedure for non-reducing sugars.

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.

What is a method to test for glucose specifically?

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.