2.1.2: Benedict’s Test

Question 1

What is Benedict’s reagent used for?

Answer 1

To test for the presence of reducing sugars

Benedict’s reagent changes color from blue to green/yellow/orange/red in the presence of reducing sugars.

Question 2

What color change indicates the presence of reducing sugars when using Benedict’s reagent?

Answer 2

Blue to green/yellow/orange/red

The more red the precipitate, the more sugar that is present.

Question 3

What is the first step in the Benedict’s test for sugars?

Answer 3

Add Benedict’s reagent to the sample

This initiates the testing process for reducing sugars.

Question 4

What type of sugar is sucrose classified as?

Answer 4

A non-reducing sugar

Sucrose cannot reduce Cu2+ due to its glycosidic bonds.

Question 5

Why can’t sucrose reduce Cu2+?

Answer 5

The chemical group needed for reduction is involved in glycosidic bonds

This prevents sucrose from participating in the reduction reaction.

Question 6

What must be done to test for non-reducing sugars?

Answer 6

Break the glycosidic bond of sucrose

This is done by acid hydrolysis, mixing with HCl and boiling.

Question 7

What is the procedure to confirm if a sugar is non-reducing?

Answer 7

1. Mix sucrose with HCl and boil. 2. Cool and add sodium hydroxide. 3. Add Benedict’s reagent and heat.

Boiling is essential to break the glycosidic bond.

Question 8

What is the role of sodium hydroxide in the non-reducing sugar test?

Answer 8

To make the solution alkaline

Benedict’s reagent only works in alkaline conditions.

Question 9

What color change indicates the presence of a non-reducing sugar after the test?

Answer 9

Blue to red

This indicates that the glycosidic bond has been broken and reducing sugars are present.

Question 10

Fill in the blank: The glycosidic bond must be broken to expose the _______.

Answer 10

reducing group

This is necessary for sucrose to be tested as a reducing sugar.