Question

What is the most widely used general test for identifying carbohydrates?

• A. Biuret Test
• B. Benedict’s Test
• C. Molisch Test
• D. Iodine Test

Hint:

Molisch Test = General test for all carbohydrates → Violet ring confirms presence.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks for a "general test" for carbohydrates, meaning a test that gives a positive result for nearly all types of carbohydrates (monosaccharides, disaccharides, and polysaccharides).
Step 2: Key Concepts in Qualitative Analysis of Biomolecules:
Different chemical tests are used to detect specific types of biomolecules or functional groups:
- Molisch Test: This is a highly sensitive chemical test for the presence of carbohydrates. Concentrated sulfuric acid dehydrates the carbohydrate to produce an aldehyde (furfural or a derivative). This aldehyde then condenses with two molecules of a phenol (α-naphthol, the Molisch reagent) to form a reddish-purple colored ring. It gives a positive result for almost all carbohydrates.
- Biuret Test: This test is used to detect the presence of peptide bonds, which means it is a general test for proteins, not carbohydrates.
- Benedict’s Test: This test is specific for reducing sugars (sugars with a free aldehyde or ketone group), such as glucose and fructose. It does not detect non-reducing sugars like sucrose or polysaccharides like starch.
- Iodine Test: This test is highly specific for starch. It does not give a positive result for simple sugars or other polysaccharides like cellulose.
Step 3: Detailed Explanation:
- Since the question asks for a general test for all carbohydrates, the Molisch Test is the most appropriate answer.
- The other tests are specific to certain subgroups (Benedict's for reducing sugars, Iodine for starch) or a different class of biomolecules entirely (Biuret for proteins).
Step 4: Final Answer:
The Molisch Test is the most widely used general test for identifying the presence of carbohydrates.