crystallization processes question

[nickelbackfan]

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So I'm trying to grasp the concept/ reasons for the steps of crystallization.

So you want to isolate a solid from impurities (are these impurities also solid?)

From what I understand, you place the solid in a solvent at room temperature. Ideally the solid isn't soluble at this temp (but some will dissolve anyway). Thus, one raises the room temperature to increase solubility.

Now I'm a little lost at this point. So does more solvent get added at high temps to saturate the solution so that the solid doesnt get dissolved? I know that by lowering the temperature, the solubility of the solid into the solvent decreases and thus crystals are formed.

Another question I have is that by increasing the temp and adding more solvent cause more impurities to be dissolved?

I am just trying to understand the general concept.

Thanks

 

[brothersport]

You have a solid with solid impurities. You want to remove these impurities.

You add solvent at room temperature.

Heat everything up so that you have a saturated solution (both the solid and impurities dissolve).

Allow to cool down. The sample will precipitate. If the solubility product of the impurity is exceeded, some of the impurity will also precipitate (although the amount will be less than originally started with.)

Repeated recrystallization will result in a purer compound because impurities lower the melting point.

 

[nickelbackfan]

thanks!