Question

A compound has a solubility in ethanol of 4.24 g/100 mL at 78°C and of 0.86 g/100 mL at 0°C

a.What volume of hot ethanol will be necessary to dissolve 50 mg of the compound? (Assume no impurities).

b.How much of the compound will remain dissolved in the solvent after recrystallization is complete? (Assume no loss of crystals).

c.What is the maximum percent recovery that could be attained?

Answer 1

a)

Since the "compound has a solubility in ethanol of 4.24 g/100 mL at 78°C",

Then

50 mg * (100 mL / 4.24 g) * (1 g / 1000 mg)

= 1.2 mL EtOH at tempreture 78°C
b)

Presuming we use the 1.2 mL EtOH and none of it boils off, then...

1.2 mL * (0.86 g / 100 mL) * (1000 mg / 1 g)

= 10.32 mg compound

This is because that is the solubility at 0°C. That's how much of the compound will remain after the solution has completely cooled off.
c)

Mass recovery

= 50.0 mg - 10.32 mg

= 39.7 mg

Percent recovery

= amt recovered / initial amt

= 39.68 mg / 50 mg * 100%

= 79.4%