Lecture notes
Carbohydrates
Covers everything in 3.1.2 in the AQA Spec. Includes the tests for non-reducing & reducing sugars and starch, monosaccharides, disaccharides and polysaccharides.
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CarbohydratesFamily of Carbohydrates
Monosaccharides - simple sugars with 1
ring or chain; 3, 5 or 6 carbons atoms. For
example: ribose, glucose. fructose.
Disaccharides - sugars with 2 rings of 6
carbon atoms joined by a glycosidic bond
(specific covalent bond). For example:
sucrose, lactose, maltose.
Polysaccharides - macromolecules with
many rings of 6 carbon atoms by glycosidic
bonds. For example: starch, glycogen,
Specification overview of this unit cellulose.
Test for Non-Reducing Sugar:
1) Sample must be in a liquid form. Add 2cm3 of HCl to 2cm3 of the sample and place in a
water bath for 5 minutes. The HCl hydrolysis any disaccharides into monosaccharides.
2) Slowly add Sodium Hydrogencarbonate to neutralise the HCl and test the pH with pH
paper to make sure the solution is alkaline. Benedict’s Reagent doesn’t work in acidic
condition
3) Add the Benedict’s Reagent and place in water bath for 5 minutes. The solution should turn
orange-brown now as reducing sugars have been produced from the hydrolsis of the non-
reducing sugars
Test for Starch:
Add two drops of iodine solution to a sample and if starch is present then it will turn BLUE-
BLACK. Not purple or anything else.
Monosaccharides:
Carbohydrates 1
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