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SupersaturationSupersaturated solutions are,to me, absolutely fascinating. They are fascinating because they exceed the solubility limit. In a sense they violate the definition of a saturated solution. When people talk about saturated solutions, there is always a temptation to say - "there is an absolute limit as to how much solute will go into the solution and you can't put any more than that in" - but you can, if you do it right. When you have a solution at its limit of solublity and you add more solute, it doesn't dissolve. That is true. But you can make it dissolve by changing the conditions. Quite often, if you heat up the solution, the solubility of the solute will increase. By heating up the solution more solute can dissolve. Once you get the "extra" solute into solution then you can cool the solution back down and sometimes keep that extra amount of solute in solution. When that does happen, you have a very unstable situation. The extra solute, the solute that "should not" have dissolved, can crystallize out of solution quite easily. If you add just a little bit of crystal, then the excess solute will crystallize out of the solution. Sometimes, all you have to do is scratch the inside of the test tube or the container that the solution is in, and it will crystalize on the scratch. I'd like to have you become familiar with this unusual kind of solution by doing the experiment with a supersaturated solution that is described in exercise 10 in your workbook when you come to the lab.
E-mail instructor: Eden Francis Clackamas Community College |
