Question

The brick red precipitate formed in Fehling's and Benedict's test is due to the

• A. Reduction of Cu²⁺ ions to Cu⁺ ions
• B. Formation of Cu(I)oxide
• C. Presence of sulphur ions in the reagents
• D. Presence of non-reducing sugars

Answer 1

The correct option is B

Formation of Cu(I)oxide

Fehling's and Benedict's solution contains cupric ions or Cu2+ ions. The Cu2+ ions are reduced to Cu+ ions by addition of electrons in the presence of reducing sugars such as glucose and maltose. The Cu+ ions in the reagent then forms Cu2O or Cu(I)oxide, which is brick red in colour. Thus Fehling's and Benedict's reagents can be used for determining the presence of reducing sugars in a sample.