PAG 9: Qualitative testing

Question 1

State the method and result for the biuret test for proteins (2)

Answer 1

1. Add sodium hydroxide solution, then copper (II) sulphate solution.
2. Positive result: colour changes from blue to purple.

Question 2

State the method and result for the iodine test for starch (2)

Answer 2

1. Add iodine in potassium iodide solution.
2. Positive result: colour changes from brown-orange to blue-black.

Question 3

State the method and result for the emulsion test for lipids (2)

Answer 3

1. Add ethanol, then pour into water.
2. Positive result: solution becomes milky in appearance.

Question 4

State the method and result for Benedict’s test for non-reducing sugars (2)

Answer 4

1. Add dilute HCl and heat in boiling water, neutralise with sodium hydrogen carbonate, then perform Benedict’s test for reducing sugars.
2. Positive result: blue changes to green, yellow, orange, or brick-red precipitate depending on concentration.

Question 4

State the method and result for Benedict’s test for reducing sugars (2)

Answer 4

1. Add Benedict’s reagent and heat in boiling water.
2. Positive result: blue changes to green, yellow, orange, or brick-red precipitate depending on concentration

Question 5

State the method and result for glucose test strips (2)

Answer 5

1. Dip test strip into the solution.
2. Positive result: colour change compared to a reference chart to determine glucose concentration