Tests for the presence of substances

Question 1

What is the method for testing for a non-reducing sugar?

Answer 1

• Add HCl, boil and cool the solution
• Add sodium hydrogencarbonate
• Add Benedict’s reagent

Question 2

What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is not present?

Answer 2

Solution remains blue

Question 3

What is observed in the Benedict’s test for a reducing sugar if a reducing sugar is present?

Answer 3

A red precipitate is formed

Question 4

Why is acid used in the Benedict’s test for a non-reducing sugar?

Answer 4

It hydrolyses the glycosidic bond

Question 5

Why is sodium hydrogencarbonate used in Benedict’s test for a non-reducing sugar?

Answer 5

Neutralises the solution as Benedict’s reagent doesn’t work in acidic conditions

Question 6

What is the test used for a reducing sugar?

Answer 6

Add an equal amount of benedict’s solution

Place in a water bath for 3 minutes

Question 7

What is observed in the Benedict’s test for a non-reducing sugar if a non-reducing sugar is present?

Answer 7

Brick red precipitate formed

Question 8

How can starch be tested for?

Answer 8

Adding potassium iodide solution

Question 9

What is observed in a positive starch test?

Answer 9

Black/dark purple solution is formed

Question 10

Describe the method for testing for the presence of proteins

Answer 10

Add Biuret’s reagent down the side of the test tube

Shake

Question 11

What is observed in a positive test for proteins?

Answer 11

Purple solution is formed

Question 12

Describe the method for testing for lipids

Answer 12

• Add ethanol and shake

- Add this solution to water and shake

Question 13

What is observed in a positive test for lipids?

Answer 13

A white emulsion is formed