CHE 104 Lecture Notes - Lecture 17: Supersaturation, Seed Crystal, Miscibility

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8 Feb 2017
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February 8th, 2017
Dr. Townsend
Lecture #17
How do we prepare a supersaturated solution?
Many materials are more soluble at higher temperatures
So, first prepare a solution at a higher temperature so more of the solute
will dissolve
Cool it down carefully
What should happen?
Should form a precipitate and have extra solute
What actually happens
If it is carefully cooled down properly, you won’t have any
crystalize
So therefore it will have more solute than it should (that’s
why they call it supersaturated)
Sometimes it can cool down without the solute crystallizing. When it does,
it then contains more solute than it would at the lower temperature.
They are not very stable, so it doesn’t take much to upset this and ruin the
outcome
By adding a seed crystal is will take away the excess solute and the
excess solute will come out of the solution
Also provides nucleation sites
Solution that still remains after this process is saturated
Figure 13.11
Just excess solute comes out not ALL of the solute
Liquids dissolving in liquids
Miscible: term used to describe two liquids that are SOLUBLE in each
other to an appreciable extent
Immiscible: term used to describe two liquids that are NOT soluble in each
other to an appreciable extent.
Liquids that are immiscible form in layers
Figure 13.4
You can see a clear difference where the layers are in the
tube, there is a blue liquid layer lying on top of the clear
liquid
Like Dissolves Like
AKA similiar dissolves similar
General rules/guidelines (there are exceptions)
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