JAMB - Chemistry (2005 - No. 28)

Sugar can be separated from its impurities in a solution primarily through crystallization, a process that allows for the separation of pure solute (sugar) from the solvent (water). Separation by evaporation method can lead to sugar charring. 

Charring of sugar is a chemical change which occurs when sugar is heated, causing it to evaporate, become foggy due to water vapor, and ultimately produce a black, powdery substance called charcoal. This process involves the breakdown of sugar molecules into carbon, water, and other volatile compounds.