Question

Slow cooling of the saturated solution promotes formation of pure crystals because the molecules of the impurities

A) Have higher solubility
B) Have lower solubility
C) Undergo chemical reactions
D) Increase in size during cooling

Answer 1

Slow cooling allows for the formation of pure crystals as impurities remain dissolved due to their higher solubility in the cooling saturated solution, separating them from the crystallizing substance through the process of recrystallization.

The correct answer is A.

Step-by-step explanation:

Slow cooling of the saturated solution promotes formation of pure crystals because the molecules of the impurities have higher solubility.

The process described is known as recrystallization. During recrystallization, a dissolved substance is crystallized (precipitated) out of the solution by cooling it down. When a saturated solution is heated, the solubility of the substance increases, allowing it to dissolve more than at lower temperatures. Upon slow cooling, the process of forming a crystalline structure begins. Pure compounds tend to crystallize out of the solution first, as they are less soluble at lower temperatures compared to the impurities. This leaves impurities in the dissolved state within the remaining solution, thus separating them from the crystallizing substance.