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Questions
Give simple chemical tests to distinguish between the following pair of compounds:
Benzaldehyde and Benzoic acid
Give simple chemical test to distinguish between Benzoic acid and Benzaldehyde.
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Solution 1
Through sodium bicarbonate:
Benzaldehyde does not react with sodium bicarbonate. However, benzoic acid will produce brisk effervescence in reaction with sodium bicarbonate, as shown in the given reaction:
\[\ce{C6H5COOH + NaHCO3 -> C6H5COO^-Na+ + CO2 ↑ + H2O}\]
\[\ce{C6H5CHO ->[NaHCO3 solution] No effervescene}\]
Through Tollen's reagent:
Benzaldehyde reacts with an ammonia solution of silver nitrate to form a silver mirror.
\[\ce{C6H5CHO + 2[Ag(NH3)2]+ + 3OH^- -> C6H5COO^- + 2Ag + 2H2O + 4NH3}\]
However, no such reaction is given by benzoic acid.
Solution 2
Benzoic acid reacts with ethanol in the presence of dilute sulphuric acid to form sweet-smelling ester Ethyl benzoate. This reaction is not given by benzaldehyde.
Notes
Students can refer to the provided solutions based on their preferred marks.
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