• Obviously the liquid ‘A’ is the aldehyde among the two because it gives a positive silver mirror test also reacts with sodium hydrogen sulphite to give a white crystalline solid (the bisulphite addition compound of the corresponding aldehyde A)
‘A’ Silver mirror
• Ketones also respond to this reaction with sodium hydrogen sulphite and form the same type crystalline addition product.
• But when it comes to tollen’s reagents ketone do not give this test because ketones do not get oxidised by mild oxidising agents for the absence of an α-H atom.
• Hence tollen’s reagent test is the clear distinction between aldehydes and ketones. Therefore in the given problem liquid, ‘A’ must be an aldehyde because it gives a positive tollen’s test and the other liquid ‘B’ must be a ketone as though it does not give tollen’s test but it reacts with NaHSO3 and forms the addition crystalline product.
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