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Choosing the right purification method depends on physical properties: Crystallization: Solid with different solubility in hot vs cold solvent. Dissolve hot, filter, cool slowly. For benzoic acid (from water), naphthalene (from alcohol), sugar. Simple Distillation: Two miscible liquids with bp difference > 25 degrees C, no azeotrope. Ether (35 C) from toluene (110 C). Fractional Distillation: Miscible liquids with bp difference < 25 degrees C. Fractionating column provides multiple theoretical plates. Acetone (56 C) from methanol (65 C). Steam Distillation: High-bp liquid that is IMMISCIBLE with water AND steam-volatile. Compound co-distills below its normal bp. Aniline (bp 184 C distills at 98 C), essential oils, nitrobenzene. Vacuum Distillation: Liquid that decomposes at its normal bp. Reduced pressure lowers bp. Glycerol (bp 290 C → 180 C under vacuum). Sublimation: Solid with high vapor pressure (solid → vapor → solid directly). Camphor, naphthalene, iodine, benzoic acid, anthracene. Differential Extraction: Compound in aqueous solution, extractable into organic solvent. Multiple small extractions better than one large (Nernst distribution law). Chromatography: Complex mixtures requiring high-resolution separation. Column/TLC (adsorption), Paper (partition). Decision tree: Is it a solid or liquid? Does it sublime? Is it miscible with water? What's the bp difference? Does it decompose? Answer these to choose.