Fehling 's solution - wikipedia Fehling 's solution Fehling 's test Fehling 's test, Left side negative, right side positive Classification Colorimetric method Analytes Monosaccharides Fehling 's solution is a chemical reagent used to differentiate between water - soluble carbohydrate and ketone functional groups, and as a test for reducing sugars and non-reducing sugars, supplementary to the Tollens ' reagent test. The test was developed by German chemist Hermann von Fehling in 1849. Contents 1 Laboratory preparation 2 Use of the reagent 3 Safety 4 See also 5 References 6 External links Laboratory preparation Fehling 's solution is prepared by combining two separate solutions, known as Fehling 's A and Fehling 's B. Fehling 's A is aqueous solution of copper ( II ) sulfate, which is deep blue. Fehling 's B is a colorless solution of aqueous potassium sodium tartarate ( also known as Rochelle salt ) made in a strong alkali, commonly with sodium hydroxide. Typically, the L - tartrate salt is used. The copper ( II ) complex in Fehling 's solution is an oxidizing agent and the active reagent in the test. The deep blue active ingredient in Fehling 's solution is the bis ( tartrate ) complex of Cu. The tartrate tetraanions serve as bidentate alkoxide ligands. Structure of the main complex in Fehling 's solution. Use of the reagent Fehling 's can be used to distinguish aldehyde vs ketone functional groups. The compound to be tested is added to the Fehling 's solution and the mixture is heated. Aldehydes are oxidized, giving a positive result, but ketones do not react, unless they are alpha - hydroxy - ketones. The bistartratocuprate ( II ) complex oxidizes the aldehyde to a carboxylate anion, and in the process the copper ( II ) ions of the complex are reduced to copper ( I ) ions. Red copper ( I ) oxide then precipitates out of the reaction mixture, which indicates a positive result i.e. that redox has taken place ( this is the same positive result as with Benedict 's solution ). A negative result is the absence of the red precipitate ; it is important to note that Fehling 's will not work with aromatic aldehydes ; in this case Tollens ' reagent should be used. Fehling 's test can be used as a generic test for monosaccharides and other reducing sugars ( e.g., maltose ). It will give a positive result for aldose monosaccharides ( due to the oxidisable aldehyde group ) but also for ketose monosaccharides, as they are converted to aldoses by the base in the reagent, and then give a positive result. Fehling 's can be used to screen for glucose in urine, thus detecting diabetes. Another use is in the breakdown of starch to convert it to glucose syrup and maltodextrins in order to measure the amount of reducing sugar, thus revealing the dextrose equivalent ( DE ) of the starch sugar. Formic acid ( HCO H ) also gives a positive Fehling 's test result, as it does with Tollens ' test and Benedict 's test also. The positive tests are consistent with it being readily oxidizable to carbon dioxide. Safety Sodium hydroxide is corrosive. See also Tollens ' reagent Benedict 's reagent Barfoed 's test References Jump up ^ H. Fehling ( 1849 ). `` Die quantitative Bestimmung von Zucker und Stärkmehl mittelst Kupfervitriol ''. Annalen der Chemie und Pharmacie. 72 ( 1 ) : 106 -- 113. doi : 10.1002 / jlac. 18490720112. Jump up ^ Hörner, T.G. ; Klüfers, P., `` The Species of Fehling 's Solution '', European Journal of Inorganic Chemistry 2016, 2016, 1798 - 1807. doi : 10.1002 / ejic. 201600168 ^ Jump up to : Fehling 's Test for Reducing Sugars External links `` Fehling 's Solution ''. Collier 's New Encyclopedia. 1921. Analytical reagents and tests Metals Aluminon Xylenol orange Sugars, fats, and proteins Sugars & Starches Benedict 's reagent ( reducing sugars etc ) Aniline acetate test ( pentoses ) Starch indicator Molisch 's test ( carbs ) Proteins & amino acids Biuret test ( proteins ) Bicinchoninic acid assay ( concentration ) Bradford protein assay ( concentration ) Lowry protein assay ( total protein ) Pierce Protein Assay ( total protein ) Tollens ' reagent ( aldehyde & ketones ) Fehling 's solution ( aldehyde & ketones ) Van Slyke determination ( amino acids ) Sakaguchi test ( arginine ) Fats Sudan stain ( lipids ) Alcohols Benedict 's reagent ( aldehyde & ketones etc ) Denigés ' reagent Lucas ' reagent ( types of alcohols ) Drugs Dille -- Koppanyi reagent ( barbiturates etc ) Ehrlich 's reagent ( indoles, etc ) Froehde reagent ( opioids ) Gallic acid reagent ( drug precursor ) Liebermann reagent ( street drugs ) Mandelin reagent ( ketamine ) Marquis reagent ( MDMA, opiates, etc ) Mecke reagent Pill testing ( general ) Simon 's reagent Zimmermann reagent ( Benzodiazepines ) Zwikker reagent ( barbiturates ) Salicylate testing other Dragendorff 's reagent ( alkaloids ) Fenton 's reagent ( creates free radicals ) Folin -- Ciocalteu reagent ( antioxidants ) Murexide test ( caffeine etc ) Melzer 's reagent ( fungi ) Marquis reagent ( various ) Nitrate test Nitrite test Luminol ( blood ) Pesticide detection kit Fecal coliform detection Prion detection kit Food portal Drink portal Category Commons Retrieved from `` https://en.wikipedia.org/w/index.php?title=Fehling%27s_solution&oldid=814559942 '' Categories : Chemical tests Coordination compounds Copper compounds Oxidizing agents Analytical reagents Hidden categories : All articles with unsourced statements Articles with unsourced statements from December 2016 Wikipedia articles incorporating a citation from Collier 's Encyclopedia Talk Contents About Wikipedia Català Čeština Dansk Deutsch Ελληνικά Español Français Galego 한국어 Bahasa Indonesia Italiano Latviešu Magyar Bahasa Melayu Nederlands 日本 語 Norsk Norsk nynorsk Polski Português Русский Slovenščina Српски / srpski Suomi Svenska Türkçe Українська 中文 Edit links This page was last edited on 9 December 2017, at 15 : 15. 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Question: how to test for a monosaccharide in an unknown liquid
Answer: Fehling's test