Recrystallization is the most common method for purifying an organic solid. This technique relies on the fact that the solubility of an organic compound often increases greatly as the solvent is heated to boiling point. When an impure solid is heated in the appropriate solvent to dissolve it, then cooled down to decrease its solubility, it will usually crystallize in a more pure form. Ideal solvent is the one that your solid is insoluble at room temperature, but soluble in hot solvent ( at boiling point).
Soluble impurities that remain dissolved in the cold solution from which the compound has crystallized ( called mother liquor)are removed by filtration. Sometimes, decolorization is necessary. Always cool the solution slowly, or else rapid recrystallization can trap impurities.
You can test and see if your sample is pure by doing a TLC or melting point, but how do you purify it. This is one way that you can do it. We are going to purify vanillin. This technique is based off of solubility. We take the actual compound that we want to purify. A lot of time it is something from the reaction that went on. You have your sample and you want to make sure that you only have that sample. The compound is different solubility from the solvent used. You want to have different solubility so that you can separate organic impurity. So you have to have something that greater than weight amount of different solubility. Something that maybe insoluble at room temperature but soluble at the boiling point is really what we are looking for. When you make it into appropriate solvent, eventually you are going to remove any impure particles, you are going to dissolve your organic compound in that solvent. So you are going to heat it up to boiling point and then cool it down. So the process of crystallization itself is to heat it with appropriate solvent, filter it, and cool it. Normally, we would get a pure form of the crystal. This is crystallization...
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