Systematic approach for identifying organic functional groups:

Step 1 — Physical examination: Note color, smell, state. Phenols have characteristic medicinal smell. Amines have fishy smell. Esters have fruity smell.

Step 2 — Solubility tests: Soluble in water → low molecular weight, polar groups (alcohols, acids, amines < C5). Soluble in NaOH → acidic compound (carboxylic acid, phenol). Soluble in NaHCO3 → strong acid (carboxylic acid ONLY — phenols are too weakly acidic). Soluble in HCl → basic compound (amine).

Step 3 — Elemental analysis (Lassaigne's test for N, S, halogens).

Step 4 — Specific functional group tests:

• Unsaturation: Br2/CCl4 decolorization or Baeyer's test (KMnO4 decolorization)
• Aldehyde: Tollens' → silver mirror; Fehling's → red precipitate; Schiff's → pink
• Ketone: 2,4-DNP positive but Tollens'/Fehling's negative
• Carboxylic acid: NaHCO3 → effervescence (CO2); litmus → red
• Phenol: FeCl3 → violet/blue/green color; does NOT react with NaHCO3
• Alcohol: Na metal → H2 gas; Lucas test $\frac{ZnCl2}{HCl}$ for 1 degree/2 degree/3 degree classification
• Primary amine: Hinsberg test soluble product; carbylamine test (CHCl3/KOH → foul-smelling isocyanide)