Benedict's reagent

Benedict's reagent (often called Benedict's qualitative solution or Benedict's solution) is a chemical reagent and complex mixture of sodium carbonate, sodium citrate, and copper(II) sulfate pentahydrate. It is often used in place of Fehling's solution to detect the presence of reducing sugars. The presence of other reducing substances also gives a positive result. Such tests that use this reagent are called the Benedict's tests. A positive test with Benedict's reagent is shown by a color change from clear blue to brick-red with a precipitate.

Generally, Benedict's test detects the presence of aldehyde groups, alpha-hydroxy-ketones, and hemiacetals, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha-hydroxy-ketone which results to a positive test because the base component of Benedict's reagent converts it into aldoses glucose and mannose. Oxidizing the reducing sugar by the cupric (Cu²⁺) complex of the reagent produces a cuprous (Cu⁺), which precipitates as insoluble red copper(I) oxide (Cu₂O).

The test is named after American chemist Stanley Rossiter Benedict.