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.