qualitative tests for carbohydrates
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Qualitative Tests for CarbohydratesTRANSCRIPT
B.S (Hons.) 3rd Semester Organic Chemistry Practicals
BS (Hons) 2nd Semester Organic Chemistry Practical Manual
ExperimentTitle:Qualitative tests for carbohydrates.
Carbohydrates are defined as the polyhydroxy aldehydes or polyhydroxy ketones or substances which form such compounds upon hydrolysis.
ExperimentsObservationsInferences
Organic compound + conc. H2SO4 + heatBlacking of colourCarbohydrate indicated
Molischs test: 2-3 mL of aqueous solution of organic compound + few drops of freshly prepared 10% -naphthol solution in alcohol (Molisch reagent) + conc. H2SO4 along the side of test tube (carefully).A violet ring at the junctionCarohydrate present
Anthrone Test: 1mL of aqueous solution of organic compound + 1mL of anthrone solution shake and warm.Green or bluish green colourationCarbohydrate present
Tests for Reducing Sugars (Such as glucose fructose, maltose, lactose etc.)
Fehlings test: 1mL of aqueous solution of organic compound + 1mL Fehlings solution + boilRed ppt.Reducing sugars (Carbohydrates) present
Benedicts test: 1mL of aqueous solution of organic compound + 1mL of Benedicts solution + boilRed ppt.Reducing sugars (Carbohydrates) present.
Tollens test: 1mL of aqueous solution of organic compound + 1mL of ammonical AgNO3 solution (Tollens reagent) + warm on water bath for 20-30 minutes.Silver mirror is produced.
Reducing sugars (Carbohydrates) present.
Organic compound + NaOH solution + heatMixture turns yellow then brown with the smell of burnt sugarReducing sugars (Carbohydrate) present
Special Tests
1 mL of aqueous solution of organic compound + dilute iodine solutionBlue colourationStarch present
1 mL of aqueous solution of organic compound + few drops of ammonium molybdate + warmBlue colourationFructose present
Cobalt nitrate solution + NaOH + organic compound Violet colourationSucrose present
1Dr. Muhammad Aslam
Assistant Professor-Chemistry
University of Education, Township Campus, Lahore.