Qualitative analysis of carbohydrates: Glucose (Unknown Sample)
| S.NO. | EXPERIMENT | OBSERVATION | INFERENCE |
| 1 | Action of heat: Heat a small amount of substance in a dry test tube. | A black residue is formed | Presence of carbohydrates |
| 2 | Action of conc.H2SO4 Take a small amount of sample solution in a dry test tube and add 2ml of conc. H2SO4 | The solution becomes black in color | Presence of carbohydrates |
| 3 | Molisch’s test: To 2 ml of given sample solution and add 5 drops of Molisch’s reagent. Then slowly add 2ml of conc. H2SO4 along the sides of the test tube. | Violet ring is formed at the junction of two layers | Presence of carbohydrates |
| 4 | Benedict’s test: To 5ml of Benedict’s reagent, add 8drops of given sample. Boil over a flame for 2 minutes or place in a boiling water bath for three minutes and allow to cool. | An appearance of green, yellow, orange or brick red precipitate. | Presence of reducing sugar like glucose, fructose, lactose and maltose. |
| 5 | Fehling’s test: To the given sample solution, add fehling’s A & B solution. Boil for 15 minutes on the water bath. | Brick red colour precipitate is formed | Presence of reducing sugars |
| 6 | Tollen’s Mirror test: To 2ml of tollen’s reagent add 2ml of sugar solution, mix well and boil for 2 minutes | Silver mirror is formed | Presence of reducing sugars |
| 7 | Barfoed’s test: To 2ml of Barfoed’s reagent, add 1ml of sample solution and heat in boiling water bath for 2 minutes (or) boil directly for 30 seconds. Cool under running tap water. | Red precipitate is formed in 1 minute | Presence of monosaccharide |
| 8 | Seliwanoff’s test: To 2.5ml of seliwanoff’s reagent add 5 drops of sugar solution and heat the mixture to boil for 30 seconds and cool. | No cherry red colour is formed. | Presence of glucose |
| 9 | Foulger’s test: Take 3ml of foulger’s reagent add 5 drops of sugar solution boil and leave the test tube in the rack | Green colour is formed | Presence of glucose |
| 10 | Osazone test: Take 10ml of sample solution in a dry test tube. Add one spatula full of phenyl hydrazine and two spatulas full of sodium acetate and 1ml of glacial acetic acid. Mix well and filtered in a test tube. Filtrate is kept in boiling water bath for 30 minutes. And examine the shape of the crystal under the microscope. | Dark yellow broomstick or needle-like appearance | Presence of glucose and fructose. |
Result
The given unknown sample was found to be Glucose
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