teaching demo 3

Activity 6AQualitative test for

Carbohydrates

ObjectivesTo determine the common carbohydrates. To identify the significant difference in the chemical properties of carbohydrates.Discuss the principle of each test.

Types of Carbohydrates Monosaccharide is a simple sugar consist only of one unit. They serve as building blocks for more complex carbohydrate forms.

Glucose, Fructose, Galactose

Disaccharides are a group of sugars composed of two monosaccharide groups linked together through the loss of sugar.

Maltose, Sucrose, Lactose

Polysaccharides are complex carbohydrates composed of numerous monosaccharides combined through the loss of water molecules.

Starch, Glycogen

Molisch Test ( Procedure )Place 1ml of distilled H2O (control)

1 ml of 5% (glucose, galactose, maltose, fructose, sucrose, lactose, glycogen & starch sol’n in each test tube

Add5 drops of Molisch Reagent

Mix content by gently shaking each tube

Incline tube while adding 1ml. conc. Sulfuric acid

Note the color of the ring formed at the junction of 2 liquids.

In the same manner add sulfuric aci to the control tube.

Record results.

Anthrone Test ( Procedure )Mix 1ml. of glucose sol’n & iml. Anthrone reagent

Stand (sometime) &note color after 30 mins, dilute with glacial acetic acid or 50% H2SO4

Do the same with 5% (galactose, maltose, fructose, sucrose, lactose, glycogen & starch)

Phenylhydrazine Test (Osazone Formation) Procedure

In each of 8 test tube place 1ml. of 5% sol’n of (#1-glucose, #2- maltose, #3-fructose, #4-galactose, #5-lactose, #6-sucrose, #7- glycogen, #8-starch)

Add a pinch of phenylhydrazine /test tube. Mix &stopper the test tubes (using cotton) Place them in boiling H2O for 30 min. Cool slowly @ room temperatue Examine crystals formed under a microscope.

Result and Observation

Documentation

 Molisch’s Test A sensitive test for all carbohydrates and some compunds containing carboydrates. Based on the dehydration of the carbohydrate by sulfuric acid to produce an aldehyde either (furfural or a derivative) which then condenses with the phenolic structure resulting in a purple-colored compound.

Anthrone Test Carbohydrates are dehydrated by using conc. H2SO4 to form furfural, which in turn condenses with anthrone to form a bluish-green complex. Sugars react with the anthrone reagent under acidic conditions to yield a blue-green color. Concentrated H2SO4 is a powerful dehydrating agent involved in dehydrating sugars leading to formation of the furfural, which condenses the anthrone to give a colored a product.

Phenylhydrazine Test (Osazone Formation) Osazones are formed when the sugars react with a compound known as phenylhydrazine at boiling point.

The reaction is stepwise; first, phenyl hydrazine reacts with carbonyl group of the sugar to form phenyl hydrazone, which then reacts with two further molecules of phenyl hydrazine to form the osazone.

Phenylhydrazine Test (Osazone Formation)

AnalysisIn Molisch Test, from the experiment all sugar tested solutions yield positive result since they are all carbohydrates. While the control tube which contains water give a negative result which is a clear solution. Since it’s not a carbohydrate.

In the Anthrone Test, only glycogen & starch give positive results but, supposedly all sugar solutions must give positive results in the Anthrone Test since they are all carbohydrates but due to some factors in the process of testing them that’s why some didn’t gave positive results.

In the Osazone Test, all tested sugar solutions gave a yellow-pale orange coloration. But some sugar solutions, when they are viewed under the microscope they didn’t give expected results (crystals formation). This is maybe because other sugar tested solutions takes longer than the time given time to form their crystals that’s why some didn’t yield a positive crystals formation (glucose & sucrose), while other yield positive results (galactose, fructose, lactose, maltose, glycogen & starch).

Conclusion

Using Molisch, Anthrone & Osazone qualitative test we became familiar with common principles of carbohydrates in different qualitative tests. We learned also their significant similarities & differences in their reactions in different qualitative tests. We knew also that external factors in theprocess of testing them would affect their reactions & results.