Benedict's Reagent

Benedict's reagent (also called Benedict's solution or Benedict's test) is a chemical reagent named after an American chemist, Stanley Rossiter Benedict

Benedict's reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and many disaccharides, including lactose and maltose. Even more generally, Benedict's test will detect the presence of aldehydes, and alpha-hydroxy-ketones, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent.

The copper sulphate in Benedict's solution reacts with reducing sugars. Benedict's solution can be used to tell if there is a sugar in a substance such as glucose in starch. One litre of Benedict's reagent can be prepared from 100 g of anhydrous sodium carbonate, 173 g of sodium citrate and 17.3 g of copper(II) sulfate pentahydrate. It is often used in place of Fehling's solution.

Benedict's reagent contains blue copper(II) ions (Cu2+) which are reduced to copper(I) ions (Cu+). These are precipitated as red copper(I) oxide which is insoluble in water.