Name: Debi M.
Date: 2001 - 2002
How and why does the least nonpolar substance dissolve
first in a nonpolar solution?
There is an old chemical mantra: "Likes dissolves Likes" but that does not
tell you much about why. The answer is complex because the solution process
is a complex process, but here is a simplified view:
For a solid to dissolve in a solvent, the atoms/molecules must be separated
from the solid. This process requires an input of energy of some sort. An
analogy is the boiling of a liquid, where there must be sufficient thermal
energy (high enough temperature) so that some of the molecules have enough
energy to escape the liquid.
In the case of solution of a solid by a solvent, the solvation of the
atoms/molecules by the solvent must be sufficiently strong to overcome the
forces holding the solid together and also to keep the atoms/molecules in
Nonpolar solvents, where only van der Waals force operate (approximately),
these forces are not strong enough to overcome the polar and/or ionic forces
that hold those types of solid solutes together. Non-polar solid solutes,
e.g. paraffin, are held together by van der Waals forces (approximately), so
the solvent has a competitive chance to dissolve such solutes.
This is very simplified, because there is no detailed theory that can
predict solubility reliably. As I said above, the process of the dissolution
of solids is a complex business.
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Update: June 2012