Question

Practice Questions: Carbon Compounds 1. You test a sample with Biuret reagent, and observe a blue color at the end of the test. Which of the following statements is the best conclusion for this test result? A. You conclude that the sample has no starch. B. You conclude that the sample has no protein. C. You conclude that the sample has no lipid. D. You conclude that the sample has no reducing sugars. E. The test for starch was positive, just like when water is tested. 2. To test for starch, you could use which of the following tests? A. Benedict's test B. Lugol's lodine test C. Biuret test D. E. Sudan IV test Paper spot test If you perform a Sudan IV test, and get a red layer on top of the sample, this indicates D. E. 3. A. B. C. The sample has protein The sample has starch The sample is water The sample has lipid None of the above is true of this test result. . If you test a water sample with Benedict's reagent, which of the following statements is true? A. B. C. the result should appear negative. the result should appear positive. the result cannot be anticipated - that's why we're testing the water. D. the result should have a reddish orange precipitate after boiling. none of the above is true of the expected test result with water. E.

Answer 1

1)B

Biuret test :

-Biuret Reagent is an aqueous solution of potassium sodium tartrate treated with cupric sulfate and sodium hydroxide.

- This test is used to detect the peptide bond.

- In the presence of peptide bond the copper (II) ione form violet pink colour coordination compound in am alkaline solutions.

- blue colour indicate absent of peptide bond i.e sample has no protein.

2) A

Benedict's test

- Benedict's reagent
It is a complex mixture of sodium carbonate, sodium citrate and copper(II) sulphate pentahydrate.

- A positive test with Benedict's reagent is shown by a color change from clear blue to a brick-red precipitate.

4) A

- Water plus Benedict's reagent is a negative control for the sugar test.

3) D

- It is used to detect the lipid in the given sample.

- Dark red Sudan IV is added to a solution along with ethanol to dissolve any possible lipids.

- If lipids are present the Sudan IV will stain them reddish-orange on the top of the layer and therefore two layer is formed.

- In negative result the orange colour is evenly distributed in column and has only one layer.