Question

PJ’s unknown solid 1) dissolves in hot ethanol, 2) is essentially insoluble in hexane, and 3) is insoluble in cold water, but sparingly soluble in warm water. Outline the recrystallization procedure you would suggest she use here.

Answer 1

1) dissolves in hot ethanol,

2) is essentially insoluble in hexane,

3) is insoluble in cold water, but sparingly soluble in warm water.

Recrystallization:

First,

use water, since it is "sparingly soluble"

Then, add plenty of hot water; then some will dissolve

Decrease tempearutre until T = "cold" that is, insoluble in water

then, filter material

Try again; increase T, so some material gets in solution at hot temperature

then, cool once again, get filtered crystals away

Notes:

The ethanol data:

not useful, since it is soluble in "hot" solution, but no "cold" solution data on solubility

hexane data:

Won't help, since it will never be soluble in it.