Benedicts's Test for Reducing Sugars

Alkaline solutions of copper are reduced by sugars having a free aldehyde or ketone group, with the formation of colored cuprous oxide. Benedict's solution is composed of copper sulfate, sodium carbonate, and sodium citrate (pH 10.5). The citrate will form soluble complex ions with Cu++, preventing the precipitation of CuCO3 in alkaline solutions.


Method

Add 1 ml of the solution to be tested to 5 ml of Benedict's solution, and shake each tube. Place the tube in a boiling water bath and heat for 3 minutes. Remove the tubes from the heat and allow them to cool. Formation of a green, red, or yellow precipitate is a positive test for reducing sugars.