Sunday, October 11, 2009

Benedict's test for the presence of a reducing sugar

Benedict's test for the presence of a reducing sugar

Benedict's reagent and Fehling's solution are used to test for the presence of a reducing sugar. The reducing sugar reduces copper(II) ions in these test solutions to copper(I), which then forms a brick red copper(I) oxide precipitate. 3,5-Dinitrosalicylic acid is another test reagent that allows quantitative spectrophotometric measurement of the amount of reducing sugar present.

Sugars having acetal or ketal linkages are not reducing sugars, as they do not form free aldehyde chains. They therefore do not react with any of the reducing-sugar test solutions. However, a non-reducing sugar can be hydrolysed using dilute hydrochloric acid to convert the acetal or ketal into a hemiacetal or hemiketal. After hydrolysis and neutralization of the acid, the product may be a reducing sugar that gives normal reactions with the test solutions.

All carbohydrates respond positively to Molisch's reagent.
Benedict's test for reducing sugars
Benedicts test for reducing sugars-how-is-brick-red-coloration-formed


  1. But how do you perform the test for Reducing Sugar? But otherwise very well written and includes some fascinating details.

  2. Hi I was just wondering if the benedicts test can detect really small amounts of sugar, say a lemon and lime drink dilute 1 in 1000