Tests for carbohydrates practical

Authors Avatar

Results

Non – Quantitative Test for reducing sugars (1, 2, and 3)

Test for Non-reducing sugars (4, 5, and 6)

Test for Starch

Iodine colour = Red/Brown

Iodine added to solution = Blue/Black

The when boiling goes = Colourless

Then when cooled = Blue/Black

Questions

1) Explain fully of all the tests?

  1. Non – Quantitative Test for reducing sugars 

All three test tubes initial colour is blue. This blue comes from the Benedict’s solution as it is made up of Copper Sulphate (which gives it the blue colour) and Sodium Hydroxide (used to make the solution alkali) which is colourless. When the Benedict’s reagent is added to test tube 1 (glucose) and heated it produces a copper oxide precipitate, this is because glucose is a reducing sugar due to it being able to change Cu 2+ to Cu+ forming the copper oxide precipitate. The colour of copper oxide is a rusty brown/red colour (final colour).

Join now!

In test tube 2 when Benedict’s reagent is added the colour is blue also. It does not reduce the copper sulphate as the bonds between the fructose and glucose have not been broken and therefore sucrose remains to be sucrose and therefore not a reducing sugar.

Test tube 3 (Starch) is also initially blue. It does not change colour in neither tests, this proves that starch is neither a reducing or non-reducing sugar, as it cannot reduce copper sulphate to copper oxide.

Test tube 4 (Glucose) starts with blue and finishes with brown. This happens because ...

This is a preview of the whole essay