Experiment 38

Objective

To identify the presence of carbohydrates in a sample using the Molisch test.

Introduction

The Molisch test is a qualitative test for carbohydrates. When a carbohydrate solution is mixed with phenol (Molisch reagent) and concentrated sulfuric acid, a red or violet-colored ring form at the interface between the acid and the carbohydrate solution, indicating the presence of carbohydrates.

Materials

Chemicals

·       Carbohydrate solution

·       Concentrated sulfuric acid (H₂SO₄)

·       Phenol (Molisch reagent)

Apparatus

·       Two test tubes

·       Two test tube holders

·       Dropper

·       Bunsen burner (optional for other heating needs)

Reagents

·       Prepare a carbohydrate solution by dissolving 3.659 g of carbohydrate in 250 ml of distilled water.

Procedure

1.    Place the carbohydrate solution in a test tube and secure it in a test tube holder.

2.    Add a few drops of Molisch reagent (phenol) to the test tube.

3.    Carefully add concentrated sulfuric acid along the side of the test tube to create a separate layer below the carbohydrate solution.

4.    Observe the formation of a colored ring at the interface of the two layers.

Observation

A red or violet-colored ring form at the interface, indicating the presence of carbohydrates.

Questions

1.    What is a carbohydrate?

2.    How are carbohydrates identified in this test?

3.    What is Molisch reagent?

4.    What is the Molisch test?