Aliphatic aldehydes and reducing sugars will form a yellow-to-red precipitate with Benedict's reagent, causing the blue solution to appear green-to-red.  This reaction can be used as a test for such aldehydes.


RCHO + 2Cu(citrate)22+ → RCOOH + Cu2O(s) + H2O

To Conduct Demonstration:  

  1. Measure 5mL 0.1% glucose solution into a 200mm test tube.
  2. Add 5mL Benedict's reagent to the tube.
  3. Place the test tube into a beaker of boiling water for 5 minutes.
  4. Measure 5mL Benedict's reagent and 5mL water into a second test tube and place in the boiling water (as a control).
  5. Place both test tubes in a lighted display rack for comparison.

 Safety and Disposal 

Wear gloves and avoid contact with skin by solutions.  Handle hot water bath with care.


D.J. Pasto and C.R. Johnson, Laboratory Text for Organic Chemistry, p 409,1979.


Margaret Asirvatham, Spring 1992