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Questions and Answers
What is the primary function of the Molisch test?
What is the primary function of the Molisch test?
- To analyze the structure of polysaccharides
- To detect the presence of sugar alcohols
- To indicate the presence of sugars (correct)
- To identify the type of sugar present
What happens when aldohexose and ketose sugars are heated with strong, concentrated mineral acids?
What happens when aldohexose and ketose sugars are heated with strong, concentrated mineral acids?
- They are converted into sugar alcohols
- They are converted into polysaccharides
- They are dehydrated to form furfural or its derivatives (correct)
- They are broken down into disaccharides
What is the first step in the Molisch test when testing disaccharides and polysaccharides?
What is the first step in the Molisch test when testing disaccharides and polysaccharides?
- Dehydration of the sugars
- Hydrolysis of the glycosidic bonds (correct)
- Formation of furfural derivatives
- Condensation with α-Naphtol
What is the role of α-Naphtol in the Molisch test?
What is the role of α-Naphtol in the Molisch test?
Why does the Molisch test take longer with polysaccharides?
Why does the Molisch test take longer with polysaccharides?
What is not detected by the Molisch test?
What is not detected by the Molisch test?
Flashcards
Molisch Test
Molisch Test
A chemical test used to detect the presence of carbohydrates (sugars).
Sugars + Strong Acids
Sugars + Strong Acids
Simple sugars like glucose and fructose are dehydrated to form furfural or its derivatives.
Polysaccharide Hydrolysis
Polysaccharide Hydrolysis
Long chains of sugars (like starch or cellulose) need to be broken down into smaller units before forming furfural.
Alpha-Naphthol
Alpha-Naphthol
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Molisch Test and Polysaccharides
Molisch Test and Polysaccharides
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What the Molisch Test Doesn't Detect
What the Molisch Test Doesn't Detect
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Study Notes
Molisch Test
- A general non-selective test used to indicate the presence of sugars, including monosaccharides, disaccharides, and polysaccharides.
- The test is negative for sugar alcohols, such as sorbitol, mannitol, and 2-deoxy-2-amino acid.
Properties of Sugars
- Monosaccharides are stable in dilute mineral acids, even when heated.
- When heated with strong, concentrated mineral acids (e.g., H2SO4), aldohexose, aldopentose, and ketose sugars undergo dehydration, forming furfural or furfural derivatives.
Detection Mechanism
- Furfural and its derivatives readily condense with α-Naphtol and certain other phenolic compounds to form highly colored products.
- In disaccharides (e.g., sucrose) and polysaccharides (e.g., starch, cellulose), concentrated acid first hydrolyzes the glycosidic bonds between the monomer sugars.
- This releases the "building block subunits" as monosaccharide sugars, which are then dehydrated by the acid to form furfural or its derivatives.
Limitations
- The test is generally slower with polysaccharides.
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