L4(not required practical) Test for reducing and non-reducing sugars

1. What is a qualitative test?

2. What is a quantitative test?

3. What is a semi-quantitative test?

4. what are reducing sugars?

1. A test which indicates whether a substance is present or not.

2.A test that allows the concentration of a substance that is present to be determined .

3. The degree of colour change can give an indication of the concentration of the reducing sugar present.

4. All monosaccharides and some disaccharides (maltose and lactose)

Benedict’s reagent is a blue solution (used to test for sugars) that contains __1? (II) sulfate ions (CuSO4); in the presence of a reducing sugar copper (I) __2? forms.

Copper (I) oxide is not __3? so it forms a __4?

1.copper. 2.oxide. 3.soluble. 4.precipitate

How do you test for reducing sugars?

1.Add Benedict’s reagent to a sample solution in a test tube

2.Heat the test tube in a water bath that has been brought to a boil for a few minutes

3.Make sure there is an excess of Benedict’s solution in the test tube.

5.Negative test- solution remains blue Positive test- green,yellow orange (low-medium reducing sugar conc). Brown/Brick red (high reducing sugar conc)

6.This test is semi-quantitative since the degree if colour change gives us an idea of the concentration of reducing sugar present.

How to test for non-reducing sugars?

1. (Following up a negative Benedict’s test) Add dilute hydrochloric acid to the sample and heat in a water bath that has been brought to the boil.

2. Cool the solution and neutralise the solution with sodium hydrogencarbonate.

3. Use a suitable indicator i.e red litmus paper to identify when the solution has been neutralised and then add a little more sodium hydrogen carbonate as the conditions need to be slightly alkaline for the Benedict’s test to work.

4.Then add Benedict’s reagent test and heat

5. Positive result: green,yellow,orange,brick-red