Qualitative Tests for Carbohydrates

Questions and Answers

What is the general test for carbohydrates?

Benedict's test

Iodine test

Barfoed's test

Molisch test (correct)

What indicates a positive result in the Glucose Molisch test?

Violet ring

What color change indicates a positive result in the Iodine test?

Purple/black

What indicates a negative result in the Iodine test for Glucose, Water, and Maltose?

Blue Signup and view all the answers

What color is observed in the Iodine test for Starch?

Blue-black Signup and view all the answers

What is tested using Benedict's test?

Reducing sugars Signup and view all the answers

What color indicates a positive result for glucose in the Benedict's test?

Brick red Signup and view all the answers

What result is observed for Sucrose in the Benedict's test?

Negative, blue Signup and view all the answers

Which test identifies monosaccharides?

Barfoed's test Signup and view all the answers

What does a positive Barfoed's test for glucose indicate?

Brick-red Signup and view all the answers

Which sugar is a ketohexose?

Fructose Signup and view all the answers

Match the following tests with their results for Sucrose:

Molisch = Purple ring Iodine = Clear yellow solution Benedict's = Clear blue solution Barfoed's = Clear blue solution for 5 and 10 minutes Seliwanoff's = Cherry-red for 5 and 10 minutes Signup and view all the answers

Match the following tests with results for Water:

Molisch = Clear colorless solution Iodine = Clear yellow solution Benedict's = Clear blue solution Barfoed's = Clear blue solution for 5 and 10 minutes Seliwanoff's = Light yellow solution for 5 and 10 minutes Signup and view all the answers

Match the following tests with results for Starch:

Molisch = Clear colorless solution Iodine = Blue-black solution Benedict's = Clear blue solution Barfoed's = Clear blue solution for 5 and 10 minutes Seliwanoff's = Light yellow solution for 5 and 10 minutes Signup and view all the answers

Study Notes

Carbohydrate Testing Methods

Molisch Test: A general test for the presence of carbohydrates, indicating a positive result with a violet ring.
Glucose & Sucrose Molisch Test: Both yield a positive result with a violet ring.

Starch Testing

Iodine Test: Used to detect starch by adding potassium iodide solution; a positive result shows a color change to purple/black.
Glucose, Water, Maltose Iodine Test: These do not yield a positive result, indicated by a negative (yellow) outcome since they are not polysaccharides.
Starch Iodine Test: A positive response is indicated by a blue-black color.

Reducing Sugar Tests

Benedict's Test: A biochemical reaction to identify reducing sugars; a positive result appears brick red.
Positive Reducing Sugars: Glucose, maltose, and fructose all produce a brick red result with Benedict's.
Negative Reducing Sugars: Sucrose and starch remain blue, indicating they are not reducing sugars.

Monosaccharide Identification

Barfoed's Test: Specifically tests for monosaccharides; a positive result for glucose and fructose is brick-red.
Maltose Barfoed's Test: Yields a positive result after 10 minutes, indicating it is a disaccharide.
Negative Monosaccharides: Sucrose and starch both return a blue result, indicating they are not monosaccharides.

Aldohexose vs Ketohexose

Seliwanoff's Test: Distinguishes between aldohexoses and ketohexoses, particularly effective for fructose.
Fructose & Sucrose Seliwanoff's Test: A positive reaction shows deep red, demonstrating fructose presence.

Summary of Test Results

Molisch Test: Violet ring for carbohydrates, clear colorless for water, blue-black for starch, indicates presence of glucose and sucrose.
Iodine Test: Clear yellow with non-polysaccharides, blue-black for starch.
Benedict's Test: Clear blue solution for non-reducing sugars (sucrose, starch).
Barfoed's Test: Clear blue for polysaccharides, brick red for monosaccharides (glucose, fructose).
Seliwanoff's Test: Cherry-red when fructose is present, light yellow suggests water or negative results for non-sugars.

Description

This quiz covers important qualitative tests for carbohydrates, including the Molisch test and the Iodine test for starch. It aims to enhance your understanding of the chemical characteristics of common carbohydrates through key definitions and results. Test your knowledge and prepare effectively for your lab sessions!