Here is a list of top eight experiments on reducing actions of glucose and fructose: 1. Reduction of methylene blue 2. Reduction of alkaline ferrcyanide 3. Tommer’s test 4. Fehlings test 5. Benedicts test 6. Picric acid test 7. Nylander’s test 8. Rapid furfural test.

Contents:

  1. Experiment on the Reduction of methylene blue
  2. Experiment on the Reduction of alkaline ferrcyanide
  3. Experiment on Tommer’s test
  4. Experiment on Fehlings test
  5. Experiment on Benedicts test
  6. Experiment on Picric acid test
  7. Experiment on Nylander’s test
  8. Experiment on Rapid furfural test

Experiment # 1. Reduction of methylene blue:

Procedure:

ADVERTISEMENTS:

In a test tube take 3 cc of distilled water, then add a drop of methylene blue (1%) and then add 0.5 cc of 40 per cent NaOH. Boil the solution. Colour is not discharged, blue colour remains. Add 1 cc of 0.2 per cent glucose or fructose solution and boil.

Result:

The solution is decolorized due to the formation of leuco-methylene blue, the reduction product of methylene blue.

Experiment # 2. Reduction of alkaline ferrcyanide:

Procedure:

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In a test tube take 3 cc of 1 per cent potassium ferricyanide solution and add 1 cc of 40 per cent NaOH solution. Boil the solution. Add 0.2 per cent glucose solution to the hot solution drop-by-drop and keep on boiling.

Result:

The yellow colour of ferricyanide begins to fade and finally decolorizes.

Experiment # 3. Tommer’s test:

Procedure:

ADVERTISEMENTS:

In a test tube take 2 cc of 0.5 per cent copper sulphate solution, then add 2 cc of 0.2 per cent glucose solution and mix. Add 2 cc of 40 per cent NaOH solution. A clear blue solution is obtained. Glucose acts as a solvent for cupric hydroxide Cu(OH)2 and prevents its precipitation. Boil.

Result:

Yellow or red precipitate of Cu2O is formed due to the reduction of CuSO4.

2Cu(OH)2 –O → CU2O + 2H2O

Experiment # 4. Fehlings test:

Procedure:

Take 5 cc of Fehling’s solution and boil. There is no change of colour on the formation of precipitate. (In case of colour change and precipitate formation reject the solution). Add 1 cc of glucose solution and boil again.

Result:

Colour changes with the formation of yellow or brick-red precipitate of Cu2O.

Experiment # 5. Benedicts test:

Procedure:

ADVERTISEMENTS:

In a test tube take 5 cc of Benedict’s reagent, then add 0.5 cc of glucose solution and heat to boiling. Boil for 2 minutes. Cool the solution under tap water.

Result:

Green yellow or red precipitate of Cu2O is formed.

Experiment # 6. Picric acid test:

Procedure:

In a test tube take 3 cc of 2 per rent glucose solution, then add 1 cc of picric acid saturated solution and then add 1 cc of 40 per cent NaOH.

Result:

Picric acid is reduced to picramic acid with the formation of red colour.

C6H2OH(NO2)3 +3H2 → C6H2OH → NH2(NO2)2 + 2H2O

Experiment # 7. Nylander’s test:

Procedure:

In a test tube take 5 cc of 2 per cent glucose solution, add 0.5 cc of Nylander’s reagent and heat to boiling and keep on boiling for 1 minute.

Result:

The solution becomes dark black, as bismuth sub-nitrate is reduced to bismuth.

Bi(OH)2NO3 + KOH → Bi(OH)3 + KNO3

2Bi(OH)3 + 3O → 2Bi + 3H2O

Experiment # 8. Rapid furfural test:

Procedure:

Take 1 cc of 2 per cent fructose solution, add 6 drops of α-naphthol, then add 5 cc of conc. HCl in a test tube and boil.

Result:

As the mixture begins to boil, deep purple colour appears.

(3) Disaccharides:

Direccharides include lactose, maltose and sucrose.

(1) Lactose:

Found in milk and also in the urine of women during pregnancy and lactation.

(2) Maltose:

It is final product of starch hydrolysis.

(3) Sucrose:

Abundant in plants as a reserve food material. Lactose and maltose are reducing sugars and give positive Tommer’s Fehling’s, Benedict’s and Barfoed’s tests. Sucrose gives positive Rapid Furfural and Seliwanoffs tests. Lactose and maltose form osazones with characteristic crystalline forms and they can be classified by microscopic examinations.

Lactosazone forms mushroom-shaped crystals, glucosazone forms needle-shaped crystals, while maltosazone forms flower-shaped crystals. Sucrose does not form osazone. For the osazone formation prepare 0.5 per cent glucose and fructose solutions, 2 per cent lactose, 2 per cent maltose and 2 per cent sucrose.

In a test tube take 5 cc of sugar solution and add 10 drops of glacial acetic acid, then add a knife point of phenyl hydrazine hydrochloride, then add double the amount of sodium acetate crystals. Give a little heat to the solution to dissolve the solids. Filter the solution and keep the filtrate in boiling water bath for 20 minutes, then remove and examine.

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