Cleaning up an impure organic solid

1
Recrystallizations

• Cleaning up an impure organic solid

2
Selecting a suitable solvent

• A bit of the compound is placed into a number of
  different COLD solvents.

3
If the compound dissolves immediately, then

• it is TOO soluble in those solvents. Those are
  rejected.

4
The remaining samples are HEATED. If the
substance

• WILL NOT dissolve those solvents are NOT
  SUITABLE.
• Those solvents are rejected.

5
Those in which the substance DISSOLVES, are then
COOLED.

• Those in which the substance re-deposits
  (recrystallizes)
• ARE SUITABLE SOLVENTS.

6
Then, the choice can be made based on a number of
factors, such as ready availability,
reaonable cot,toxicity, flammability, etc.
7
The impure substance is heated in thechosen
solvent until dissolved.A bit of excess solvent
is desirable.
8
Hotplates are now available and may be a better
option than the burner especially if the solvent
is FLAMMABLE!
9
Any undissolved impurity is removed by gravity
filtration.
10
The clear filtrate is cooled in an
ice-waterslurry until crystallization is
complete.
11
The purified crystals are collected on Buchner
funnel with suction.Use the thick-wall vacuum
tubing NOT the thin-wall gas/water hoses.
12
Spread the damp product on a watch glass or clay
plate and place it safely in your lab drawer.
13
Nothing is turned in today.Next week (or
sometime during the week) when the product is
dried, determine its M.P., its mass, and the
percent recovered.
14
Record the data in your notebook FIRST!

• AFTER the data has been recorded, the product is
  correctly labeled and turned in with your
  Laboratory Report.

15

• If you are in my section, check the bulletin
  board to see if you have CLEAN-UP duties this
  week.