Carbohydrates

Carbohydrate – disaccharides and polysacchairdes:
Monosaccharides join together in pairs to for disaccharides. They join by a molecule of water being removed from between them, which is called a condensation reaction, and leaves the two monosaccharides joined by oxygen, which is a glycocydic bond.
The test for non-reducing sugars is to do the Benedict’s reagent test (put 2cm3 in test tube, add equal volumes of Benedict’s, and then boil for five minutes.) If this remains blue, however, then, add another 2cm3 of the sample to 2cm3 of dilute hydrochloric acid and boil for five minutes, to hydrolyse the disaccharide into monosaccharides, and then add sodium hydrogen carbonate, to neutralise the HCl, as the Benedict’s won’t work in acidic conditions. You then re-test the solution with Benedict’s (add equal volumes, boil for five minutes), and if the precipitate goes brown, a non reducing sugar was present, due to the reducing sugars made in hydrolysis.
1) Lactose is made up of Glucose and Galactose
Sucrose is made up of Glucose and Fructose
Starch is made from Alpha glucose and Alpha Glucose.
2) Formula of sucrose = C12H22O5

The test for starch is using Potassium Iodide solution from a change in colour from yellow to blue-black when 2 drops of potassium iodide is added to 2cm3 of a sample.