Test of glucose
(i) When heated in a waterless test tube, it melts, turns brown and finally black, giving a characteristic smell of burnt sugar.
(ii) When warmed with a little conc. H2SO4, it leaves a charred residue of carbon.
(iii) When it is boiled with dilute NaOH solution, it first turns yellow and then brown.
(iv) Molisch's test : This is a general test for carbohydrates. Three or Two drops of alcoholic solvent of a-naphthol are included to 2mL of glucose solution. 1 mL of concentrated H2SO4 is added carefully along the sides of the test tube. The creation of a violet ring, at the junction of two liquids defines the presence of a carbohydrate.
(v) Silver mirror test : A mixture of glucose and ammonical silver nitrate is warmed in a test tube. Existence of silver mirror on the inner walls confirms glucose.
(vi) Fehling's solution test : A little glucose is warmed with Fehling's solution. A red color precipitate of cuprous oxide is created.
(vii) Osazone formation : Glucose on heating with excess of phenyl hydrazine in acetic acid gives a yellow crystalline substance, m.pt. 205oC.
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