1. Briefly explain why you should not heat organic solvents over a Bunsen burner flame.
2. Indicate a procedure to solve the following recrystallization problems.
(a) oiling out
(b) lack of crystal formation
(c) presence of colored impurities
3. Compound A, a white crystalline solid with a melting point of 75°C, has the solubility profile shown
in the following table. Which of the solvents listed would be a good recrystallizing solvent for
Compound A? Briefly explain.
Compound A — solubility profile
solvent solvent boiling pt. solubility at 25°C solubility at boiling point
water 100. c insol. sol.
methanol 65°C insol. sol.
acetone 56°C sol. sol.
diethyl ether 35°C sol. sol.
4. A student purified a 500. mg sample of phthalic acid by recrystallization from water. The published
solubility of phthalic acid in 100. mL of water is 0.54 g at 14°C and 18 g at 100.°C. You must show your
calculations for the questions below.
(a) What is the smallest volume of boiling water the student could use to dissolve 500. mg of phthalic
acid?
(b) Dissolution of phthalic acid in boiling water produced a clear solution. The student allowed the
solution to cool, then put the solution in an ice bath. Crystals formed, and the student isolated 380 mg of
phthalic acid. Calculate the percent recovery of phthalic acid in this experiment.
