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Q.
Aldehydes and ketones can be distinguished by:
Delhi UMET/DPMTDelhi UMET/DPMT 2002
Solution:
The reagent used to distinguish aldehydes and ketones is one with which either aldehyde or ketone reacts.
[a] Lucas test: It is used to distinguish between $1^{\circ},2^{\circ}$ and $3^{\circ} $ alcohols.
The Lucas reagent is anhydrous $ZnCl_{2}$ and cone. $HCl$.
[b] Tollens reagent: It is ammoniacal silver nitrate solution. Aldehydes reduce it to silver mirror whereas ketones dont react with it.
So, Tollens reagent is used to distinguish between aldehydes and ketones.
[c] Molisch test: It is used to detect the presence of carbohydrate in solution. Formation of violet coloured ring at the junction of ale. a-naphthol solution and cone. $H_{2}SO_{4}$ shows the presence of carbohydrate in the food.