Molisch’s Test is one of the simplest and most common tests used in laboratories to check if a substance contains carbohydrates. It’s a general test for all types of carbohydrates, whether simple sugars or complex ones. Even though the test is quick and easy to perform, it gives clear results and helps in identifying the presence of carbohydrates in a sample. In this article, you’ll learn about the principle behind the test, the chemicals used, the steps to follow and how to understand the results. This test is often asked in board exams and practicals, so having a clear understanding can really help you prepare better.

What is Molisch Test?

Molisch Test is a confirmatory qualitative test for carbohydrates. α-naphthol in ethanol is called molisch's reagent, which is added to a carbohydrate-contained sample in a test tube. After that, a few drops of sulphuric acid are added to it. Ultimately, a purple ring is generated in the middle of the test tube. Almost all carbohydrates (except tetroses & trioses) give positive Molisch Test. Furthermore, some glycoproteins and nucleic acids come in contact with strong mineral acids from monosaccharides, giving a positive Molisch Test.

Few examples of Molisch Test Reaction:

• Molisch Test for Starch
• Molisch Test for Glucose

During the reaction, applying sulphuric acid can remove the water molecules from the given carbohydrate; hence aldehyde is generated. The α-naphthol in molisch's reagent undergoes condensation with the aldehyde, forming a reddish-purple-coloured complex. A detailed feature of the Molisch Test on D-glucose is provided below to understand the reaction's mechanism better.

Reagent’s Required for Molisch Test 

Molisch Test Reagent and apparatus are:

• Dry Test Tubes
• Solutions: Glucose 5%, Sucrose 5%, Starch 5%
• H2SO4
• Pipettes
• 5% α naphthol in ethanol ( Molisch reagent)

Procedure Of Molisch Test 

• 2 ml of the sample is poured into a dry test tube
• 2ml of distilled water is added in another test tube to be considered as a control
• 2-3 drops of Molisch's reagent are added to each test tube
• 1 ml concentrated 
• H2SO4 is pipetted out and added along the tube's wall to produce two different levels.
• The colour arises and shifts at the junction of two layers.
• The formation of a purple ring at the junction indicates the presence of carbohydrates.

Result of Molisch Test Experiment

If carbohydrate is present in the given sample, then after conducting the Molisch test Experiment, a purple-coloured ring appears at the junction of the two layers in a test tube.

Applications of Molish’s Test

• Used to detect carbohydrates in food, plant extracts, and other biological samples.
• Helps in lab experiments to confirm the presence of sugars before doing more specific tests.
• Commonly used in schools and college practicals to teach basic carbohydrate testing.
• Supports biochemical research by identifying sugar-coating compounds in unknown substances.

Limitations of Molish’s Test

• It only tells you if carbohydrates are present, but not which type.
• Other substances may sometimes give a false positive result, making it less specific.
• Strong acid used in the test can be dangerous if not handled carefully
• Not useful for very small amounts of carbohydrates, as the result may not be clearly visible.

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