How would you distinguish experimentally between an alcohol and a carboxylic acid?
Carboxylic acids and alcohols can be distinguished experimentally by their reaction with carbonates and hydrogencarbonates.
When a carboxylic acid (like ethanoic acid) is treated with sodium carbonate or sodium hydrogencarbonate, it reacts to produce a salt, carbon dioxide gas, and water. The carbon dioxide gas is released as brisk effervescence (bubbles).
On the other hand, alcohols do not react with carbonates or hydrogencarbonates. No effervescence or gas is produced when alcohol is treated with these compounds.
Therefore, the appearance of effervescence on adding sodium carbonate or sodium hydrogencarbonate indicates the presence of a carboxylic acid, while the absence of such reaction indicates an alcohol.
Explanation
The textbook context explicitly mentions the reaction of ethanoic acid (a carboxylic acid) with carbonates and hydrogencarbonates to produce carbon dioxide gas, water, and a salt (sodium acetate). This reaction is unique to carboxylic acids and does not occur with alcohols. The chemical equations provided (2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2 and CH3COOH + NaHCO3 → CH3COONa + H2O + CO2) demonstrate this distinguishing reaction. This is a standard 2-mark answer format that directly addresses the experimental distinction.
Solution Steps
Step 1: Take the given compound in a test tube.
Step 2: Add sodium carbonate (Na2CO3) or sodium hydrogencarbonate (NaHCO3) to it.
Step 3: Observe for effervescence (bubbles of carbon dioxide gas).
Step 4: If brisk effervescence occurs, the compound is a carboxylic acid. If no reaction occurs, it is an alcohol.