Q.(i) Write Tollen's reagent test for acetaldehyde.

Acetaldehyde reduces Tollen's reagent to metallic silver (mirror test); sulfanilic acid is a zwitterion; diazo coupling of the diazonium salt with phenol gives an azo dye.

1. Tollen's reagent test for acetaldehyde: On warming acetaldehyde with Tollen's reagent (ammoniacal silver nitrate, $[Ag(NH_3)_2]^+$), the aldehyde is oxidised to acetate ion while $Ag^+$ is reduced to metallic silver, which deposits as a bright silver mirror on the inner wall of the test tube. $CH_3CHO + 2[Ag(NH_3)_2]^+ + 3OH^- \rightarrow CH_3COO^- + 2Ag\downarrow + 4NH_3 + 2H_2O$
2. Zwitterion of sulfanilic acid: Sulfanilic acid (4-aminobenzenesulfonic acid) exists as an internal salt (zwitterion), with the strongly acidic $-SO_3H$ group protonating the basic $-NH_2$ group: $^{+}H_3N-C_6H_4-SO_3^-$ (para-substituted) …