Fehling's solution

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Fehling's solution
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Fehling's solution is the name given to a chemical reagent, primarily used to differentiate between water-soluble carbohydrate and ketone functional groups. It can also be used as a test for reducing sugars and non reducing sugars. This reagent is prepared from two solutions, a basic solution of potassium sodium tartrate and a solution of copper(II) sulfate.





Reagent "A" and Reagent "B" are available from Sigma Aldrich.


  • Fehling's "A" uses 7 g CuSO4·5H2O dissolved in distilled water containing 2 drops of dilute sulfuric acid.
  • Fehling's "B" uses 35g of potassium tartrate and 12g of NaOH in 100 ml of distilled water.

These two solutions should be stoppered and stored until needed.

For the test: Mix 15 ml of solution-"A" with 15 ml of solution-"B" Add 2 ml of this mixture to an empty test tube. Add 3 drops of the compound to be tested to the tube. Place the tube in a water-bath at 60° C.

A positive test is indicated by a green suspension and a red precipitate





Solution A and B should be stored separately in tightly stoppered bottles. They are stable under normal temperatures and pressures.



Preparation from UWI at Mona, Jamaica: [[1]]

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