Barfoed's Test

Barfoed's Test

           Barfoed's Test is used to detect the presence of monosaccharides in an unknown sample solution.


Principle:

In this reaction copper (ll) acetate reduces to copper(I) oxide (brick red ppt.).


Only reducing  sugar responses in this test, not by the non -reducing sugar.



Experiment 

Observation 

Inference 

To about 1 ml of sample solution, 2 ml Barfoed's reagent was added and the mixture was boiled in a water bath  for 1- 2 minutes.

Brick red ppt or crimson red ppt appeared within 2 minutes of boiling.

Reducing sugar present in the sample.Since brick red ppt of copper(ll) oxide appeared within 2  minutes of heating the sample contains glucose/ fructose/galactose

( monosaccharides).

If there is no response within 3 minutes of boiling , then it the boiling continued upto 10 minutes.

Brick red ppt of copper (ll) oxide settled at the bottom of the test tube very slowly.

The sample contains reducing sugar and it is disaccharide (lactose, maltose ,etc).

Boiling continued for more than 10 minutes.

No change.

There is no reducing sugar  present in the sample solution.

The sample may contain non reducing sucrose.



Barfoed's reagent is a week acidic solution. It is prepared by dissolving 13.3 gm copper (ll) acetate in 200 ml of 1% acetic acid solution.

 

Reactions:-

  1. Cu(CH3COO) +2 H2O → 2 CH3COOH +Cu(OH)2

  2. Cu(OH)2→ CuO +H2O

  3. D-glucose+ 2 CuO → D-gluconic acid +Cu2O (brick red ppt.)




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