3: Testing for carbohydrates

Question 1

What type of sugars are monosaccharides and disaccharides?

Answer 1

Reducing sugars

Question 2

What is the chemical test for a reducing sugar?

Answer 2

Benedict’s test

Question 3

How do you carry out a Benedict’s test?

Answer 3

1. Place the sample in a boiling tube. If it is not in liquid form, grind it up or blend it in water.
2. Add an equal volume of Benedict’s reagent.
3. Heat the mixture gently in a boiling water bath for five minutes.

Question 4

What is the colour change for a positive Benedict’s test for reducing sugars?

Answer 4

Blue to brick red

Question 5

What type of sugar is sucrose?

Answer 5

Non-reducing sugar

Question 6

How do you carry out a Benedict’s test for non-reducing sugars?

Answer 6

Boil the non-reducing sugar (eg sucrose) with dilute hydrochloric acid. It will then give a positive result when warmed with Benedict’s solution

Question 7

What test is used for the presence of starch?

Answer 7

Iodine test

Question 8

How do you carry out an iodine test?

Answer 8

Add a few drops of iodine dissolved in potassium iodide solution to the sample

Question 9

What is the colour change for a positive iodine test for starch?

Answer 9

Yellow to black

Question 10

What can reagent strips test for?

Answer 10

Presence of reducing sugars (most commonly glucose)

Question 11

What is an advantage of using reagent strips?

Answer 11

With the use of a colour-coded chart, the concentration of the sugar can be determined