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I had a fairly simple question regarding supersaturation and crystallization. When a supersaturated solution is crystallized, is all of the solute crystallized or just the excess solute (such that the solution remains saturated)? After crystallization, would you expect to find some quantity of the solute still dissolved?

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    $\begingroup$ Yes, only the excess solute crystallises - the solution is still saturated (but not supersaturated) afterwards. $\endgroup$ – Gerhard May 24 '15 at 9:21
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Think of it this way: A saturated solution is the equilibrium. Say you had a supersaturated solution, formed a crystal out of it and somehow managed to get your solution below saturation.

But once that happened, your solution is no longer saturated and there is undissolved material on the ground (your crystal). So, always striving towards equilibrium, some of your crystal would get redissolved to re-reach the saturation.

In fact, crystallisation and equilibrium are not static but rather dynamic processes. So even if there is a crystal sitting at the bottom and it looks like nothing is happening, there is a constant flux of compounds redissolving from the crystal surface or recrystallising onto the surface out of the solution. Which is also why everything seems to strive towards the equilibrium: It is the state, where the speed of one direction matches that of the other direction.

So short answer: The solution above a crystal will be saturated, but no longer supersaturated.

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