Final answer:
Dissolving an impure compound in hot solvent is done to exploit the increased solubility at higher temperatures, allowing both impurities and the pure compound to dissolve better, with the pure compound precipitating upon cooling for easier separation.
Step-by-step explanation:
When you dissolve an impure compound in a hot solvent, the goal is to take advantage of the increased solubility of the compound at higher temperatures. This means that as the temperature of the solvent increases, the amount of the solute that can be dissolved in the solvent also increases. Hot solvents have more kinetic energy, which leads to more frequent and forceful collisions between solvent molecules and the solute, helping to break down the lattice of the crystalline solid and allowing it to dissolve into the solution. Both the pure compound and the impurities will dissolve better in the hot solvent; however, upon cooling, the pure compound is less soluble and thus will precipitate out of solution, whereas the impurities remain dissolved, which can then be separated out through filtration or other means.
Therefore, the correct answer to why you dissolve the impure compound in hot solvent is d) both the impurities and the pure compound will dissolve better in hot solvent.