Many students confuse the Benedict's Test for Non-Reducing Sugars with the Benedict's Test for Reducing Sugars, perhaps because some of the steps in the procedure are similar. A liquid food sample does not need prior preparation except dilution if viscous or concentrated.For a solid sample prepare a test solution by crushing the food and adding a moderate amount of distilled water.
The test for non-reducing sugars is often conducted on a food sample which tested negative for reducing sugar.If reducing sugars have been shown to be present, a heavier precipitate is often observed when the test for non-reducing sugar is conducted. This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.
When the concentration of reducing sugar is low, the color of the Benedict's test may be light green or pale orange.
As non-reducing sugars do not have the aldehyde group, they cannot reduce copper (I) (blue) to the copper(II) (red).Sucrose is the most common disaccharide non-reducing sugar.


Sodium hydrogen carbonate is necessary for neutrallization as the reduction of the copper(II) ions will not take place in acidic conditions - of excess acid is present.
The blue copper(II) ions from copper(II) sulphate are reduced to red copper(I) ions by the aldehyde groups in the reducing sugars.
Sodium carbonate provides the alkaline conditions which are required for the redox reaction above. Sodium citrate complexes with the copper (II) ions so that they do not deteriorate to copper(I) ions during storage. However it is less popular as it less sensitive and requires that the reagents - Fehling's solutions A and B - be kept separate until the experiment is carried out. This accounts for the colour changes observed.The red copper(I) oxide formed is insoluble in water and is precipitated out of solution.


We can use this reaction to find out if a food or other substance contains a reducing sugar. This accounts for the precipitate formed.As the concentration of reducing sugar increases, the nearer the final colour is to brick-red and the greater the precipitate formed.



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