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