Rate of crystal formation and concentration

partyatmygaff

There's something that's been bugging me for a while about an assignment I have to write up. Say I have a supersaturated solution of an organic compound that happens to be contaminated with minute amounts of various different impurities.

Is the reason for the growing crystal lattice favouring similar molecules down to the fact that they fit better in the lattice or is it down to the huge difference in concentration between the compound and its contaminants?

krd

partyatmygaff wrote: »

Is the reason for the growing crystal lattice favouring similar molecules down to the fact that they fit better in the lattice or is it down to the huge difference in concentration between the compound and its contaminants?

It would be both.

But it gets a little more complicated. Impurities can help crystals seed.

If you take a plastic bottle of pure water - distilled, with all impurities removed - then heat it to remove any oxygen. Then seal the bottle, and put it in a deep freeze. The water will remain liquid well below it's freezing point. When you take it out and open it, the water on exposure to air will rapidly freeze.

Water crystals need an initial seed to get going. I think it could be become similar molecules, when they're free, repel each other. I think once the crystal gets going, it has an affinity for other crystals of the same molecule.

I'm not sure - a supersaturate mix, could do two things. If there are impurities in the solution (something tells me they have to be right for seeding) the excess in the solution will precipitate into crystals. If, there isn't impurities in the solution, that allow for crystal seeding, the solution may instead become more viscous.

Crystals are crazy things. Just think about snowflakes.



Insane