Unit 2 - Testing For Carbohydrates

Question 1

What is Benedict’s test for

Answer 1

Reducing sugars, which are all monosaccharides and some disaccharides like maltose and lactose
This means that can reduce another molecule (donate electrons)

Question 2

How to do a Benedict’s test (alkaline solution of copper 11 sulfate)

Answer 2

1) place sample in a boiling tube. If not liquid, grind it up or blend in with water.
2) add an equal volume of Benedict’s reagent
3) heat in water bath for 5 minutes

The reducing sugars will react with the copper ions. This results in the copper 2+ gaining electrons, reducing them into brick red ions. Brick red precipitate forms if positive result

Question 3

Most common non reducing sugar

Answer 3

Sucrose

Question 4

Sucrose will give a positive non reducing sugar test when

Answer 4

Boiled with dilute hcl, as the acid will hydrolyse (hydrolysis) into glucose and fructose, which are monosaccharides so reducing sugars.

Question 5

Test for starch

Answer 5

Iodine

Question 6

Iodine test for starch procedure

Answer 6

1) add few drops of iodine dissolves in potassium iodide solution are mixed with sample
2) if colour change is from yellow-brown to blue-black, starch is present

Question 7

What do reagent strips allow?

Answer 7

Test presence of reducing sugar, eg glucose
Advantage is that using a colour coding chart, can decifer the concentration of the sugar also