Question

Write Tollen's reagent test for acetaldehyde.

Hint:

Only aldehydes (aliphatic and aromatic) and alpha-hydroxy ketones give a positive Tollen's test. Simple ketones do not.

Answer 1

Step 1: Understanding the Concept:
Tollen's reagent (ammoniacal silver nitrate) is a mild oxidizing agent that oxidizes aldehydes but not ketones.
Step 3: Detailed Explanation:
When acetaldehyde (\(CH_3CHO\)) is heated with Tollen's reagent \([Ag(NH_3)_2]^+\), the aldehyde is oxidized to an acetate ion.
Simultaneously, the silver ions (\(Ag^+\)) are reduced to metallic silver (\(Ag\)).
This silver deposits on the inner wall of the test tube, forming a shiny "silver mirror".
Reaction:
\[ CH_3CHO + 2[Ag(NH_3)_2]^+ + 3OH^- \rightarrow CH_3COO^- + 2Ag \downarrow + 4NH_3 + 2H_2O \]
Step 4: Final Answer:
Acetaldehyde reduces Tollen's reagent to produce a silver mirror.