Fehling's solution


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Fehling's solution

(fā`lĭngz), deep-blue, alkaline solution used to test for the presence of aldehydesaldehyde
[alcohol + New Lat. dehydrogenatus=dehydrogenated], any of a class of organic compounds that contain the carbonyl group, , and in which the carbonyl group is bonded to at least one hydrogen; the general formula for an aldehyde is RCHO, where R is hydrogen
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 (e.g., formaldehyde, HCHO) or other compounds that contain the aldehyde functional group, -CHO. The substance to be tested is heated with Fehling's solution; formation of a brick-red precipitate indicates the presence of the aldehyde group. Simple sugars (e.g., glucose) give a positive test, so the solution has been used to test for the presence of glucose in urine, a symptom of diabetes; Benedict's solutionBenedict's solution,
deep-blue alkaline solution used to test for the presence of the aldehyde functional group, −CHO. The substance to be tested is heated with Benedict's solution; formation of a brick-red precipitate indicates presence of the aldehyde group.
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, which gives the same test, is now more widely used. Fehling's solution is prepared just before use by mixing equal volumes of two previously prepared solutions, one containing about 70 grams cupric sulfate pentahydrate per liter of solution and the other containing about 350 grams Rochelle salt (potassium sodium tartrate tetrahydrate) and 100 grams sodium hydroxide per liter of solution. The cupric ion (complexed with tartrate ion) is reduced to cuprous ion by the aldehyde (which is oxidized) and precipitates as cuprous oxide (Cu2O); for this reason, sugars that react with Fehling's solution are called reducing sugars.
References in periodicals archive ?
Subsequently some drops of the Fehling's solution A and B were supplemented.
The total carbohydrate content was determined by dinitrosalicylic (DNS) method (Browning, 1963) while qualitative test for carbohydrate was done with Fehling's solution (Furniss et al.
After hydrolysis, the presence of carbohydrates in the hydrolyzed samples was investigated by different biochemical tests including Molisch Test, Iodine Test, Benedict's Test, Tollen Test, Barfoed's Test, Fehling's solution Test, Osazone Test, Seliwanoff's Test and Bial's Test.
Each filtrate was heated with 5 ml of equal volume of Fehling's solution A and B in a test tube.