General Scheme for Identification of Unknown Carbohydrate Physical

General Scheme for Identification of Unknown Carbohydrate

Physical properties: a- Condition: b- Color: c- Odor: d- Taste: e- Effect on litmus paper: N. B. : shake the polysaccharides well before transferring to test tube.

Chemical tests: Unknown carbohydrate Fehling’s test No reddish brown ppt. (non-reducing carbohydrate) Reddish brown ppt. of Cu 2 O (Reducing carbohydrate) N/50 I 2 soln. No change in I 2 color (Gum acacia or sucrose) Benzidine test Blue color (Gum acacia) Olive green color with suspended blue particles (Gum tragacanth) Blue color (Starch) Brick red particles (Agar-agar) No blue color (Not gum acacia) Resorcin test Red color (Sucrose)

Confirmatory test for all the previous unknowns is: Hydrolysis then Fehling’s test Reddish brown ppt. of Cu 2 O For Agar-agar: (test for sulfate ions) Hydrolysis then Ba. Cl 2 test White ppt. of Ba. SO 4

Fehling’s test Reddish brown ppt. of Cu 2 O (Reducing carbohydrate) Barfoed’s test Reddish brown ppt. of Cu 2 O within 5 min. (Monosaccharide) No reddish brown ppt. of Cu 2 O within 5 min. (Disaccharide) Ozazone test Yellow ppt. after 15 min. on hot, shows raphides under microscope (Glucose or Fructose) Resorcin test Red color (Fructose) No red color (Glucose) Ozazone test Yellow ppt. after 45 min. after cooling, shows tufts of needles under microscope (Lactose) Yellow ppt. after 45 min. after cooling, shows radiating plates or broad needles under microscope (Maltose)

Fehling’s test: 1 ml sugar soln. 1 ml Fehling’s A 1 ml Fehling’s B heat on water bath Reddish brown ppt. of Cu 2 O

Barfoed’s test: 1 ml sugar soln. 1 ml Barfoed’s reagent Heat on boiling W. B. for 5 min. Reddish brown ppt. of Cu 2 O at the bottom of the test tube

Ozazone test: 5 ml sugar soln. 0. 5 g Phenylhydrazine HCl 1 g Sodium acetate Heat on W. B. for 15 -45 min. Yellow ppt. on hot, when examined under microscope shows ………………

Resorcin (Selwianoff’s) test: 2 ml sugar soln. 2 ml 12%HCl or conc. HCl Few crystals of resorcin Heat on W. B Deep red colour

Test with N/50 I 2 soln. : 2 ml of the carbohydrate soln. (shake) N/50 I 2 soln. (amount? ) Starch Gum tragacanth Agar-agar Blue colour Olive green colour Brick red particles

Benzidine test (oxidase test) : 2 ml of gum acacia soln. (shake) Few drops 10% H 2 O 2 soln. 1 -2 drops of benzidine Blue colour

Ba. Cl 2 Test (test for sulfate ions) (Agar-Agar): 3 ml of the Agar-agar soln. (shake) 3 ml of dil. HCl Put in W. B. for 30 min. Neutralize, Few drops of Ba. Cl 2 soln. White turbidity or ppt. of Ba. SO 4

Hydrolysis then Fehling’s (confirmatory test): 3 ml of the carbohydrate soln. (shake) 3 ml of dil. HCl Put in W. B. for 30 min. Neutralize with sodium bicarbonate Carry out Fehling’s test Reddish brown ppt. of Cu 2 O

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