Benedict 's reagent - wikipedia Benedict 's reagent `` Benedict 's '' redirects here. For other uses, see Benedict ( disambiguation ). This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. Please help to improve this article by introducing more precise citations. ( May 2015 ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( May 2015 ) Benedict 's test Positive Benedict 's test Classification Colorimetric method Analytes Reducing sugars Benedict 's reagent ( often called Benedict 's qualitative solution or Benedict 's solution ) is a chemical reagent named after American chemist Stanley Rossiter Benedict. It is a complex mixture of sodium carbonate, sodium citrate and copper ( II ) sulfate pentahydrate. It is often used in place of Fehling 's solution to detect the presence of reducing sugars. The presence of other reducing substances also gives a positive reaction. Such tests that use this reagent are called the Benedict 's tests. A positive test with Benedict 's reagent is shown by a color change from clear blue to a brick - red precipitate. Generally, Benedict 's test detects the presence of aldehydes and alpha - hydroxy - ketones, also by hemiacetal, including those that occur in certain ketoses. Thus, although the ketose fructose is not strictly a reducing sugar, it is an alpha - hydroxy - ketone, and gives a positive test because it is converted to the aldoses glucose and mannose by the base in the reagent. The principle of Benedict 's test is that when reducing sugars are heated in the presence of an alkali they are converted to powerful reducing species known as enediols. Enediols reduce the cupric compounds ( Cu ) present in the Benedict 's reagent to cuprous compounds ( Cu ) which are precipitated as insoluble red copper ( I ) oxide ( Cu O ). The color of the obtained precipitate gives an idea about the quantity of sugar present in the solution, hence the test is semi-quantitative. A greenish precipitate indicates about 0.5 g % concentration ; yellow precipitate indicates 1 g % concentration ; orange indicates 1.5 g % and red indicates 2 g % or higher concentration. Contents 1 Benedict 's test 2 Benedict 's solution 3 Quantitative reagent 4 See also 5 References Benedict 's test To test for the presence of monosaccharides and reducing disaccharide sugars in food, the food sample is dissolved in water, and a small amount of Benedict 's reagent is added. During a water bath, which is usually 4 -- 10 minutes, the solution should progress in the colors of blue ( with no reducing sugar present ), orange, yellow, green, red, and then brick red precipitate or brown ( with high reducing sugar present ). A color change would signify the presence of a reducing sugar. The common disaccharides lactose and maltose are directly detected by Benedict 's reagent because each contains a glucose with a free reducing aldehyde moiety, after isomerization. Sucrose ( table sugar ) contains two sugars ( fructose and glucose ) joined by their glycosidic bond in such a way as to prevent the glucose isomerizing to aldehyde, or the fructose to alpha - hydroxy - ketone form. Sucrose is thus a non-reducing sugar which does not react with Benedict 's reagent. Sucrose indirectly produces a positive result with Benedict 's reagent if heated with dilute hydrochloric acid prior to the test, although after this treatment it is no longer sucrose. The acidic conditions and heat break the glycosidic bond in sucrose through hydrolysis. The products of sucrose decomposition are glucose and fructose, both of which can be detected by Benedict 's reagent, as described above. Starches do not react or react very poorly with Benedict 's reagent, due to the relatively small number of reducing sugar moieties, which occur only at the ends of carbohydrate chains. Inositol ( myoinositol ) is another carbohydrate which produces a negative test. Benedict 's reagent can be used to test for the presence of glucose in urine. Glucose in urine is called glucosuria and can be indicative of diabetes mellitus, but the test is not recommended or used for the diagnosis of diabetes mellitus. A false positive reaction can be due to the presence of other reducing substances in urine such as ascorbic acid ( during intake of vitamin supplements ), drugs ( levodopa, contrast used in radiological procedures ) and homogentisic acid ( alkaptonuria ). Benedict 's solution Benedict 's solution is a deep - blue solution used to test for the presence of the aldehyde functional group, - CHO. It is an aqueous alkaline mixture of CuSO and sodium citrate. Here sodium citrate is the complexing agent that keeps Cu in solution, which would otherwise precipitate as cupric carbonate. The substance to be tested is heated up to 95 ° C ( for example, in a water bath ) with Benedict 's solution ; formation of a brick - red precipitate indicates presence of the aldehyde group in relatively high concentrations. Since simple sugars ( e.g., glucose ) give a positive test, the solution is used to test for the presence of glucose in urine, a symptom of diabetes. One litre of Benedict 's solution contains 173 grammes sodium citrate, 100 grammes sodium carbonate, and 17.3 grammes cupric sulphate pentahydrate. It reacts chemically similarly to Fehling 's solution ; the cupric ion ( complexed with citrate ions ) is reduced to cuprous ion by the aldehyde group ( which is oxidised ), and precipitates as cuprous oxide, Cu O. Experiment Observation Inference Substance in water + 3ml Benedict 's solution, then boil for few minutes and allow to cool. Red, green, or yellow precipitate is obtained Reducing sugar e.g. Glucose is present Substance in water + 3ml Benedict 's solution, then boil for few minutes and allow to cool. Solution remains clear or is a little blue Reducing sugar is not present Quantitative reagent Benedict 's quantitative reagent contains potassium thiocyanate and is used to determine how much reducing sugar is present. This solution forms a copper thiocyanate precipitate which is white and can be used in a titration. The titration should be repeated with 1 % glucose solution instead of the sample for calibration. See also Other oxidizing reagents Dextrose equivalent Tollens ' reagent Fehling 's solution Other reducing reagents ( opposite ) Jones reductor Walden reductor References Jump up ^ Benedict, S.R. 7 ( 1 January 1909 ). `` A Reagent For the Detection of Reducing Sugars '' ( PDF ). J. Biol. Chem. 5 ( 6 ) : 485 -- 487. Jump up ^ Robert D. Simoni ; Robert L. Hill & Martha Vaughan ( 2002 ). `` Benedict 's Solution, a Reagent for Measuring Reducing Sugars : the Clinical Chemistry of Stanley R. Benedict ''. J. Biol. Chem. 277 ( 16 ) : 10 -- 11. doi : 10.1074 / jbc. M110516200. PMID 11773074. ^ Jump up to : Collins Edexcel International GCSEBiology, Student Book ( ISBN 978 - 0 - 00 - 745000 - 8 ) p. 42 - 43 Symptoms and signs relating to endocrine system, nutrition and development ( R62 -- R64, 783 ) Weight and appetite decrease : Anorexia Weight loss Cachexia Underweight increase : Polyphagia Polydipsia Orexigenia Weight gain Growth Delayed milestone Failure to thrive Short stature Idiopathic Thyroid disease General Goitre Graves ' disease Abadie 's sign of exophthalmic goiter Boston 's sign Dalrymple 's sign Stellwag 's sign lid lag Von Graefe 's sign Griffith 's sign Möbius sign Hypothyroidism Queen Anne 's sign Nutrition Rickets Harrison 's groove Benedict solution Metabolic disorders low calcium Chvostek sign Trosseau 's sign low glucose Whipple 's triad 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=Benedict%27s_reagent&oldid=823810397 '' Categories : Copper compounds Chemical tests Coordination compounds Oxidizing agents Analytical reagents Hidden categories : CS1 : Julian -- Gregorian uncertainty Articles lacking in - text citations from May 2015 All articles lacking in - text citations Articles needing additional references from May 2015 All articles needing additional references Articles with multiple maintenance issues Talk Contents About Wikipedia Deutsch Español فارسی Français 한국어 Bahasa Indonesia Italiano עברית Nederlands 日本 語 Polski Português Русский Svenska தமிழ் 中文 8 more Edit links This page was last edited on 3 February 2018, at 15 : 41. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: why do you test water with benedict's reagent
Answer: detects the presence of aldehydes and alpha-hydroxy-ketones, also by hemiacetal, including those that occur in certain ketoses