Question:medium
The functional group that can be identified through Tollens' reagent test is:
The functional group that can be identified through Tollens' reagent test is:
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Tollens' reagent gives silver mirror test with aldehydes.
Updated On: May 28, 2026
- Aldehyde
- Alcoholic
- Phenolic
- Carboxylic acid
Show Solution
The Correct Option is A
Solution and Explanation
Step 1: Understanding the Topic:
This question concerns "Qualitative Analysis" in organic chemistry. Functional groups are detected in the laboratory through specific "named" color tests. The Phthalein dye test is a sensitive method used to distinguish phenols from other oxygen-containing organic compounds like aliphatic alcohols or aldehydes. It results in the synthesis of a pH-sensitive dye that changes color in alkaline solutions.
Step 2: Key Formulas and Approach:
The approach involves understanding the condensation reaction between phenols and phthalic anhydride:
$2 \text{ Phenol} + \text{Phthalic Anhydride} \xrightarrow{H_2SO_4, \Delta} \text{Phthalein Dye} + H_2O$.
Step 3: Detailed Explanation:
Reaction Mechanism: When a compound containing a phenolic hydroxyl group ($-OH$ attached to an aromatic ring) is heated with phthalic anhydride and concentrated sulfuric acid, a condensation reaction occurs.
Dye Formation: This reaction produces a phthalein derivative. For instance, ordinary phenol produces phenolphthalein.
Identification: The reaction mixture is then treated with a dilute alkali like $NaOH$. If a phenol was present, the solution will develop a characteristic color (pink/red for phenol, green fluorescence for resorcinol).
Selectivity: Alcohols and aldehydes do not possess the correctly activated aromatic ring to undergo this specific condensation to form colored phthalein dyes. Thus, it is a specific test for the phenolic group.
Step 4: Final Answer:
The phthalein dye test is used to identify the phenolic functional group, matching option (B).
This question concerns "Qualitative Analysis" in organic chemistry. Functional groups are detected in the laboratory through specific "named" color tests. The Phthalein dye test is a sensitive method used to distinguish phenols from other oxygen-containing organic compounds like aliphatic alcohols or aldehydes. It results in the synthesis of a pH-sensitive dye that changes color in alkaline solutions.
Step 2: Key Formulas and Approach:
The approach involves understanding the condensation reaction between phenols and phthalic anhydride:
$2 \text{ Phenol} + \text{Phthalic Anhydride} \xrightarrow{H_2SO_4, \Delta} \text{Phthalein Dye} + H_2O$.
Step 3: Detailed Explanation:
Reaction Mechanism: When a compound containing a phenolic hydroxyl group ($-OH$ attached to an aromatic ring) is heated with phthalic anhydride and concentrated sulfuric acid, a condensation reaction occurs.
Dye Formation: This reaction produces a phthalein derivative. For instance, ordinary phenol produces phenolphthalein.
Identification: The reaction mixture is then treated with a dilute alkali like $NaOH$. If a phenol was present, the solution will develop a characteristic color (pink/red for phenol, green fluorescence for resorcinol).
Selectivity: Alcohols and aldehydes do not possess the correctly activated aromatic ring to undergo this specific condensation to form colored phthalein dyes. Thus, it is a specific test for the phenolic group.
Step 4: Final Answer:
The phthalein dye test is used to identify the phenolic functional group, matching option (B).
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