Aldehyde Functional Group Test || Identification of Aldehyde || Chemistry Practical || DrRajnishChem

Tests for Aldehydes: ************

2,4-Dinitrophenylhydrazine (2,4-DNP) Test:

Confirms presence of carbonyl groups in both aldehydes and ketones. On adding 2,4-DNP reagent, formation of a yellow/orange/red precipitate indicates a positive result.

Chemical reaction: R2C=O+2,4-DNP→Hydrazone derivative+H2O


Tollens’ Test (Silver Mirror Test)

Used to identify aldehyde groups specifically. Aldehydes reduce Tollens’ reagent to metallic silver, forming a shiny ‘silver mirror’ on the tube. Ketones do not react—no change observed.

Equation:
RCHO+2[Ag(NH3)2]OH→RCOONH4+2Ag↓+3NH3+H2O

Fehling’s Test:

Detects aliphatic aldehydes (not effective for aromatic aldehydes and ketones). Aldehyde reduces Fehling’s solution, producing a red-brown precipitate of copper(I) oxide (Cu2O). Ketones yield a negative result—no precipitate.


Schiff’s Test:

Aldehydes react with Schiff’s reagent to restore its pink/magenta color, confirming an aldehyde. Ketones do not change the reagent’s color.





Aldehyde Functional Group Test || Identification of Aldehyde || Chemistry Practical || DrRajnishChem