Benedict's Test: Theory

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.