Question

Acetanilide has a solubility of 1.00 g/185 ml in 25 oc water and 1.00 g/20 ml in 100 oc water. what is the minimum volume of water needed to recrystallize 500 mg of acetanilide? how much acetanilide will remain dissolved after crystallization at 25 oc?

Answer 1

In the crystallization process the solid compound is dissolved in the solvent at elevated temperature and the crystallize product obtained by slow cooling of the  solution. Here the solubility of acetanilide at 100°C is 1g per 20mL of water. Thus to dissolve 500mg of acetanilide at high temperature that is 100°C we need 10mL of water.

Now at 25°C after the re-crystallization there will be some amount of dissolve acetanilide. Which can be calculated as- 185mL of water is needed to dissolve 1g or 1000mg of acetanilide at 25°C. Thus in 10mL of water there will be $\frac{10X1000}{185}=54.05$gmg of acetanilide.