1.

Give simple chemical test to distinguish between the following pairs of compounds : (i) Benzaldehyde and benzoic acid(ii) Propanal and propanone.

Answer»

Solution :(i) Distinguish between benzaldehyde and BENZOIC ACID `:`
1. Action of sodium hydrogencarbonate solution
`underset("Benzoic acid")(C_(6) H_(5) COOH ) + NaHCO_(3) rarr C_(6)H_(5) COONa + CO_(2)uarr + H_(2) O`
`underset("Benzaldehyde")(C_(6)H_(5) CHO) + NaHCO_(3) rarr `No reaction
brisk reaction takes place with benzoic acid but not with benzaldehyde.
2. Tollen.s test
Benzaldehyde forms a bright silver mirror with Tollen.s reagent . Benzoic acid does not give this test.
`C_(6) H_(5) CHO + 2[ Ag ( NH_(3))_(2) ]^(+)+ 3OH^(-) rarrC_(6) H_(5) COO^(-) + 2Ag + 2H_(2) O + 4NH_(3)`


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