CHEM 235 - EXP. 3 - RECRYSTALLIZATION

A difference in solubility of the solids. A compound increases its solubility with increased temperature, therefore, by elevating the temperature and allowing it to cool, the compound can be recovered.

The impurities are in smaller concentrations than the desired compound (isolated from extraction) and will remain in solution under both hot and cold conditions.
If there are is large quantities of impurities, the main chief component reject them during recrystallization because they do not meet its geometry.

1) It must dissolve the compound only sparingly at room temperature or not at all. It must dissolve the compound readily at its boiling point.
2) It cannot react chemically with the compound to be purified.
3) It must have a bp lower than the melting point of the solid to be purified.
4) It should dissolve impurities well, or not at all.

Varies.
Method: add small amount continuously via the top of the condenser while the compound is being boiled until the compound just dissolves.

- Narrow neck allows for minimal evaporation.
- Contents can be swirled without spilling.
- Can be corked or stoppered so that vapor and liquid can equilibrate during crystallization.
- Ease of removal

During a recrystallization when one or both of the following are present:
a) There are insoluble impurities remaining in the solution.
b) There are coloured, soluble impurities which require use of Norit as well.

This is to prevent premature precipitation of the solid on the funnel or flask.

It is not soluble in any solvent and coloured substances adsorb onto the Norit. It can be filtered off, along with the impurities.

Addition of Celite (twice the amount of Norit) with the Norit. The Norit absorb onto the Celite surfaces thus not falling through the filter paper.