CHEMICAL TEST & IMPORTANCE OF CARBOHYDRATES 1.How can you identify carbohydrate from an unknown source? ANSWER: The following test are done for identify carbohydrate from an unknown source: 1.Molisch Test: specific for carbohydrates. This test is specific for all carbohydrates Monosaccharide gives a rapid positive test, Disaccharides and polysaccharides react slower. Method : 1-Two ml of a sample solution is placed in a test tube. 2-Two drops of the Molisch reagent (which α-napthol in 95% ethanol) is added. 3-The solution is then poured slowly into a tube containing two ml of concentrated sulfuric acid so that two layers form, producing violet ring appear as liaison between the surface separations. FIGURE: MOLISCH TEST 2.Benedict's Test: presence of reducing sugars. • All monosaccharides are reducing sugars; they all have a free reactive carbonyl group. • Some disaccharides have exposed carbonyl groups and are also reducing sugars. Other disaccharides such as sucrose are non-reducing sugars and will not react with Benedict's solution -Large polymers of glucose, such as starch, are not reducing sugars, since the concentration of hemiacetal groups is very low Method : • One ml of a sample solution is placed in a test tube. • Two ml of Benedict’s reagent(complex mixture of sodium carbonate, sodium citrate and copper(II) sulfate pentahydrate) is added. • The solution is then heated in a boiling water bath for five minutes. • A positive test is indicated by: The formation of a reddish precipitate. FIGURE: Benedict’s test 3.Barfoed's Test: test used for detecting the presence of monosaccharides. Method: • Place one ml of a sample solution in a test tube. • Add 3 ml of Barfoed's reagent (a solution of cupric acetate and acetic acid). • Heat the solution in a boiling water bath for 6 minutes(after the 3 min check the tubes) •Reducing monosaccharides are oxidized by the copper ion in solution to form a carboxylic acid and a reddish precipitate of copper (I) oxide within three minute 4. Seliwanoff's Test: distinguish between aldoses and ketoses. Used to distinguish between aldoses (like glucose) and ketoses (like fructose). Method: • One half ml of a sample solution is placed in a test tube. • Two ml of Seliwanoff's reagent (a solution of resorcinol and HCl) is added. • The solution is then heated in a boiling water bath for two minutes. • A positive test is indicated by produce a cherry red product for ketohexos & yellow to faint pink for aldohexos. FIGURE: Seliwanoff's test 2.How will you distinguish between glucose & fructose by a chemical test? Write down their pharmaceutical uses? ANSWER: Bromine water oxidizes glucose to gluconic acid when treated with it. Fructose does not react with bromine water . Bromine water is a mild (very) oxidising agent. It's not strong enough to oxidise the ketone group Fructose has. This is why they don't react. Pharmaceutical importance of glucose: a.In industry, glucose is used as a precursor to make vitamin C. b.Glucose in a fluid form is a benefit in the food industry because it is easy to mix into formulations on a big scale. c.In jams and jellies, liquid glucose can supply the osmotic pressure necessary to prevent bacterial growth and spoilage d.In the medicine-making process, liquid glucose is useful as a sweetener for syrups and tonics. e.It is also used to coat tablets and as a granulating agent. f.Liquid glucose can also be used as a medication for diabetic patients. g. Ingested orally or through injection, liquid glucose can raise blood sugar immediately. Pharmaceutical importance of fructose: a.High fructose corn syrup is used to sweeten foods and beverages b.It is used as a food for diabetic people. c.Infant feeding formula often contain fructose. d.It is an ingredient of fructose +NaCl injection.