[cherrytomb]

I'm working on my 'recrystallization of an unknown compound' lab and the only thing I don't understand is the main thing. How does the solvent that only dissolves the compound at boiling point get rid of the impurities?
My solvent is water, so that's polar and my organic compound is 4-aminobenzoic acid which is non-polar. I know that's why it doesn't dissolve in water at room temp. But then it dissolves only when water is at its boiling point, which I don't understand, and also how does that remove impurities? Sorry, I've been looking on the net for this and wish someone could explain.

[nj_bartel]

Different compounds have different solubilities.  The trick is to find the solvent that dissolves your impurities, but not your selected product (or vice versa).

[cherrytomb]

I know, but how does the solvent actually remove the impurities? Like, is it because it's at its boiling point, so it's breaking apart and it's somehow forming bonds with the impurities? But then how is it doing that? I need a more specific answer..I really want to understand what is going on

[nj_bartel]

It's the same process by which sugar dissolves in water.

Imagine you have sodium chloride and lead oxide in a finely powdered mixture together.  You add the powder to water, the sodium chloride dissolves, but the lead oxide doesn't.  You can now filter off the lead oxide, leaving the sodium chloride in solution.

[cherrytomb]

Okay, so you want a solvent that doesn't dissolve it at room temp, because then you can't really perform the recrystallization. And then you want a solvent that does dissolve it at  boiling point so that it can dissolve the impurities and hold on to them. Then when it recrystallizes, you get pure compound, I guess. Okay, well, thank you for your help.