Benedict's test is used to determine if a reducing sugar is present in a sample using a reagent called the Benedict's reagent. The reagent is an alkaline solution, containing a copper citrate complex with Cu2+ ions. When the reagent reacts with the aldehyde group of a reducing sugar, the Cu2+ ions are reduced to Cu+ ions, forming a red precipitate of cuprous oxide. In lower amounts, this precipitate appears as orange or green. The chemical reaction of the key functional groups can be viewed in Figure 1.
Figure 1 - Simplified reaction of a reducing sugar with Benedict’s reagent.