Benedict test procedure principle ( reducing sugar test)

Benedict’s test is a simple chemical that can be used to assess the presence of reducing sugars. Reducing sugars have free aldose or ketose groups, which are capable of donating electrons to other molecules by oxidizing them.

Reducing sugars are mostly monosaccharides (e.g. glucose, fructose, galactose) and some of them are disaccharides which are lactose and maltose.

The principle of Benedict’s test

Reducing sugar under alkaline conditions forms enediols. Benedict’s solution contains milder alkali Na2CO3. Enediols are powerful reducing agents.

They can reduce cupric ions (Cu +2) to cuprous ions (Cu+) which is the basis for Benedict’s reaction. The cuprous hydroxide during the process of heating is converted to red cuprous oxide.

Benedict test procedure

How to prepare Benedict’s reagent

1. Measure 17.3 grams of copper sulfate (CuSO4), 173 grams of sodium citrate (Na3C6H5O7), and 100 grams of anhydrous sodium carbonate (Na2CO3) (or 270 grams of sodium carbonate decahydrate (Na2CO3.10H2O).

2. Put all the measured chemicals in a volumetric flask of 1000 mL.
3. Pour distilled water up to 1000 mL marking.
4. Dissolve all the components properly by shaking gently.

Benedict test reagent components

• Benedict’s reagent
• Water bath
• Dry test tubes
• Positive control (5% glucose)
• Negative control (distilled water)
• Sample
• Pipettes

Benedict test Result with interpretation