Question

A saturated solution of copper (II) sulfate was prepared by adding an excess of
small crystals to a flask of water. The flask which contained the saturated
solution and many small crystals of CuSO4 was sealed and placed in a cupboard
for several months. When it was removed, most of the small crystals were gone
and several large crystals had appeared. However, the concentration of CuSO4
in the solution was unchanged. Explain, describing the events that occur at the
molecular level, how it is possible for the crystals to change without a change in
the concentration of the solution.

Answer 1

This is explained by equilibrium.
The fact that there were many small crystals at the bottom of the solution is a sign of super saturation.
CuSO4 (S) --> CuSO4 (Aq)
The equilibrium shifted to the left, forming more solids, since there was a lot of dissolved copper.
Think of it this way:
There wasn't alot of space in the water for the copper to float around in the liquid world, but there was space to be a solid. So that's what it did; became solid.

Answer 2

There wasn't enough water ions to saturate all of the copper sulfate ions, so some didn't get saturated (ie the solid at the bottom)

Answer 3

the solution isn't super saturated, just saturated. A supersaturated solution contains _more_ solute than it should at a given temp. A disturbance to the system causes crystals to crash out of the solution, but a flask with solute sitting at the botton is at its saturation point. See the link for the question asked and answered 3 times already today.

http://openstudy.com/study#/updates/4fa12effe4b029e9dc3205f1