WAEC Chemistry 2023 Paper

Concept:Fractional distillation separates components of a solution by using their different boiling points.A low-boiling liquid is vaporised and collected, leaving the less volatile solute behind.Explanation:Iodine ($\mathrm{I_2}$) dissolves in tetrachloromethane ($\mathrm{CCl_4}$) to form a single liquid solution.Tetrachloromethane is a volatile, non-polar liquid with a boiling point of about $76.8^\circ\mathrm{C}$.On gentle heating, $\mathrm{CCl_4}$ vaporises first and can be condensed and collected separately.Iodine is not vaporised appreciably at this temperature, so it remains behind in the distillation flask as residue.This method works because there is a large difference between the boiling points of the components.Solvent extraction is not suitable because iodine is more soluble in $\mathrm{CCl_4}$ than in water, so no simple immiscible solvent will selectively remove it.Decantation and filtration are also unsuitable because iodine is dissolved in the solution, not present as an undissolved solid.Answer:C. Fractional distillation