Question

Phthalic acid has a solubility of approximately 18g per 100 ml of water at 100°c and 0.62g per 100 ml of water at 25°c. what is the minimum volume of water needed to recrystallize 50 mg of phthalic acid? how much phthalic acid will remain in solution after recrystallization?

Answer 1

The minimum volume of water needed is 0.28 mL. The solution will have

1.7 mg of phthalic acid remaining in solution.

At 100 °C

Volume of water required = 50 mg HPh × (100 mL water/18 000 mg HPh)

= 0.28 mL water

At 25 °C

Mass of HPh in solution = 0.28 mL water × (620 mg HPh/100 mg water)

= 1.7 mg HPh