<P> Benedict's reagent (often called Benedict's qualitative solution or Benedict's solution) is a chemical reagent named after American chemist Stanley Rossiter Benedict . </P> <P> It is a 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 reaction . 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 a brick - red precipitate . </P> <P> Generally, Benedict's test detects the presence of aldehydes and alpha - hydroxy - ketones, also by hemiacetal, 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 . </P> <P> The principle of Benedict's test is that when reducing sugars are heated in the presence of an alkali they are converted to powerful reducing species known as enediols . Enediols reduce the cupric compounds (Cu) present in the Benedict's reagent to cuprous compounds (Cu) which are precipitated as insoluble red copper (I) oxide (Cu O). </P>

Why do you test water with benedict's reagent