Recrystallization as a method of purification relies on the solubility of the solid and the impurities, melting point difference of the solid and the impurities, difference in the boiling point of the impurities and the solvent, or all of the above?

Here are the solutions to the questions:

1. Recrystallization as a method of purification relies on the _____
A. solubility of the solid and the impurities
Recrystallization works by exploiting the difference in solubility between the desired compound and its impurities in a specific solvent at varying temperatures. The desired compound is typically much more soluble at high temperatures and less soluble at low temperatures, allowing it to crystallize out while impurities remain dissolved or crystallize differently.

2. Five grams of an organic solid is dissolved in 100 ml of H₂O (solvent 1). Which of the following extraction methods will remove the largest amount of the organic solid from the aqueous solution?
C. Three 50 ml portion extractions with ether (solvent 2).
In liquid-liquid extraction, it is more efficient to perform multiple extractions with smaller volumes of solvent than a single extraction with a larger total volume. All options use a total of 150 ml of ether, but option C uses three separate 50 ml extractions, which will extract the most organic solid.

3. A substance that decomposes below its boiling point can best be purified by _____
D. distillation under reduced pressure
Distillation under reduced pressure (vacuum distillation) lowers the external pressure, which in turn lowers the boiling point of the substance. This allows compounds that would decompose at their normal boiling point to be distilled at a lower, safer temperature, preventing degradation.