Give chemical tests to distinguish between the following pairs of compounds :
(i) Phenol and Benzoic acid
(ii) Propanal and Propanone
Ans.
To distinguish between the given pairs of compounds, we can employ various chemical tests that take advantage of the unique properties of each compound. Here are some tests for each pair:
(i) Phenol and Benzoic acid:
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Neutralization with NaHCO3: Benzoic acid, being acidic, will react with sodium bicarbonate (NaHCO3) to produce effervescence due to the liberation of carbon dioxide gas. Phenol, being a non-acidic compound, will not show this reaction.
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Formation of Esters: Benzoic acid can be converted to benzyl benzoate by reacting with ethanol in the presence of concentrated sulfuric acid as a catalyst. Phenol will not undergo this reaction.
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Bromine Water Test: Phenol, being an aromatic compound, will decolorize bromine water due to the electrophilic aromatic substitution reaction. Benzoic acid will not show this reaction.
(ii) Propanal and Propanone:
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Tollens’ Test: Propanal can be distinguished from propanone by performing the Tollens’ test. Propanal, being an aldehyde, will give a positive Tollens’ test, forming a silver mirror due to the reduction of silver ions to silver metal. Propanone will not give a positive Tollens’ test.
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2,4-Dinitrophenylhydrazine (2,4-DNP) Test: Propanal and propanone both can react with 2,4-dinitrophenylhydrazine (2,4-DNP) to form yellow or orange precipitates known as 2,4-dinitrophenylhydrazones. However, the rate of reaction may differ between the two compounds.
These tests provide effective ways to differentiate between the given pairs of compounds based on their chemical properties and reactivities.
