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Terms in this set (73)

1) Solvent Selection

An ideal solvent is one the has a steep solubility vs temperature curve with respect to the solid. The solid must be soluble in the solvent when the temperature of the solution is high (boiling), but when the temperature is lowered (room temperature) the solid must be insoluble to the solvent.

2) Dissolution

The solid being crystalized is placed inside of a test tube. Then the chosen solvent is added to the test tube one drop at a time at high temperatures. Enough of the solvent will be added to dissolve the solid. The insoluble material will not be dissolved.

3) Decolorization

This step is needed when a colored impurity must be removed from the solution. A small amount of powered charcoal is added to the hot solution because the charcoal attracts to colored impurities so these impurities can be removed when the solution is filtered.

4) Gravity Filtration

Gravity filtration via filter paper is used to collect the unwanted solid impurities (these impurities did not dissolve in solution when the solvent was heated). This includes the charcoal that was added in the decolorization step. A piece of filter paper is fluted in one direction only. It is then placed into a stemless funnel (stemless so the solid does not crystallize in the stem during this filtration step). The filtrate is collected in a flask.

5) Crystallization

Because the cold solution cannot hold as much solvent as the hot solution, the excess solid will crystallize out of solution. Using an Erlenmeyer flask, there will be both solid and liquid present once the solution slowly cools down.


6) Filtration

The Erlenmeyer flask now contains the desired solid and solvent (with a very small amount of dissolved solid contained in the solvent). The slurry mixture is poured through a filter allowing the filter to catch the desired solid while the solvent passes through. The solid is then obtained and washed with a small amount of cold liquid over the solid.

7) Dry the Solid

The filtered and washed solid is placed in a safe place to dry. Any solvent that adheres to the desired solid will evaporate leaving the pure solid.