A mixture contains solid iodine (I2) and sodium chloride (NaCl). Which separation method is most appropriate to obtain pure iodine?
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Correct answer
B. Sublimation
Principle or equation
Sublimation is the direct transition from solid to gas. Iodine sublimes readily when heated, leaving non-volatile sodium chloride behind.
Why this answer is correct
Iodine has a high vapor pressure and sublimes at moderate heat, while NaCl does not sublime. Heating the mixture causes iodine to vaporize; the vapor can be condensed on a cold surface to recover solid iodine. Filtration would not separate a solid mixture, distillation is for liquids, and chromatography is for separating components based on differential adsorption, but sublimation is the most direct and efficient here.
Example
Ammonium chloride can be separated from sodium chloride by sublimation because NH4Cl sublimes on heating.
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