Question

When 2 to 3 drops of Benedict’s reagent are added to a urine sample and heated gently, it turns yellow. This colour change indicates that
A. Urine contains 2% glucose
B. Urine contains 0.5% glucose
C. Urine contains 1.5% glucose
D. Urine contains 1% glucose

Answer 1

Benedict’s reagent is a chemical reagent which is a composition of a complex mixture of sodium citrate, sodium carbonate and copper(II) sulphate pentahydrate. It is often used to detect the presence of reducing sugar as a substitute for Fehling's solution.

Complete Answer:
- Simple carbohydrates tests can be done with the help of Benedict’s reagent. Reducing sugars like monosaccharides and few disaccharides having free aldehyde or ketone functional groups are identified by Benedict's test.
- Benedict's solution can be used to test for the presence of glucose in urine and is a test to check the presence of a reducing sugar in urine. This is done by heating Benedict's solution with a solution to be tested which yields a yellow, red, or orange precipitate upon warming with a reducing sugar such as glucose or maltose. This reaction is caused by the reducing property of simple carbohydrates.
- After conducting the Benedict test, the colour of the solution indicates the amount of glucose contained in the solution. This shows the presence of 0.1 to 0.5% glucose if the solution turns green in colour. The presence of 0.5 to 1% glucose is indicated when the solution turns.
- The presence of 1 to 1.5% glucose is indicated when the solution turns brown in colour. It shows the presence of 1.5 to 2% glucose if the solution turns red in colour. If there is more than 2% glucose content in the solution, brick red precipitate is seen in the solution. The yellow colour indicates a maximum of 1% glucose content in the solution.

Therefore the correct answer is (D) Urine contains 1% glucose.

Note: Benedict's test only gives the information about the presence or absence of sugar molecules, but it does not give any information about the sugar molecule like whether the molecule is glucose or fructose etc. This test is not suitable to all sugars. Benedict's reagent does not react with non-reducing sugars such as sucrose.