Chemistry Aldehydes & Ketones MDCAT 2019
PMDC Verified Question 60 of 94
Identification test for functional groups of organic compounds are associated with specific observations. Tollen's reagent is ammonical silver nitrate solution, which is used for the identification of a functional group X with an observation O. Identify X and O.
A
X = Aldehyde ; O = red precipitate
B
X = Ketone ; O = Silver mirror
C
X = Aldehyde ; O = Silver mirror
D
X = Ketone ; O = grey precipitate
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: X = Aldehyde ; O = Silver mirror
Concept:

Tollens' reagent is a specific chemical test used to differentiate easily oxidizable functional groups from more stable ones.

Solution:

  • Tollens' reagent reacts positively only with Aldehydes (Functional group X).


  • During the reaction, the aldehyde reduces the Silver(I) ions in the reagent to metallic silver.


  • This elemental silver coats the inside of the reaction vessel, providing the visual observation (O) known as a Silver mirror.


Why other options are incorrect:

Option A pairs aldehydes with a red precipitate, which is characteristic of Fehling's or Benedict's tests, not Tollens'. Options B and D suggest ketones react, but ketones do not undergo mild oxidation with Tollens' reagent.

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