Hey i was jsut wondernig - I was doing a recrystallization experiment and noticed that there was crystals forming int he filtrate during the vacuum filtration, i was wondering are these crystals more pure, or less or equal to my inital crystals. the organix solvents have low boiling points. does that help
I see this happen a lot too. I think it's mainly because the solution is still supersaturated with solute that has not had time to completely crystallize before filtering. Imperfections on the surface of the glass, such as scratches, provide "nucleation points" for crystals to begin forming. Scratching the sides of the container with a glass stirring rod does this also. Probably the filter paper or sintered glass frit does the same thing as the solution passes through it. And if it is a vacuum filtration and the solvent is volatile, the filtrate will become concentrated and cold in the filtering flask, which helps further crystallization also. This portion may be more pure if it crystallizes slowly as nice crystals with well-formed faces, but otherwise its purity is probably about the same as the rest of the batch.
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