To me, these questions sound a lot like homework
questions. So I've decided to point you in the
right direction rather than simply give the
answers to the questions directly. Hopefully,
this will clear up any confusion you have about
the questions. Good luck.
1.Does propylene glycol dissociate in
Well, I think you need to know something
specific about propylene glycol to answer this
question, which makes it hard for me to answer for
It is much easier to first think about salt,
that is NaCl. When you drop a chunk of sodium
chloride in water, it will dissociate into ions.
Why? Since the salt dissociates into ions
which are oppositely charged and, hence,
attractive, it might seem weird that dissociation
will occur. After all, aren't the ions going
to want to continue to stick together?
However, there is also entropy to consider.
In other words, there are many, many more
configurations available for the ions to be
dissociated in the water, and so some very large
fraction of the ions will prefer to be in the
water. In this case the entropy beats out the
attraction between ions.
Remember that almost all of chemistry can be
reduced to the competition between energy and
entropy. Chemists have invented numbers to
measure this competition for chemical reactions,
namely equilibrium constants.
Presumably, the same sort of reasoning can be
applied to propylene glycol. It's up to you to
figure out the answer to your specific question,
2. Will a 1.0 m copper(II) sulfate solution
have the same freezing-point depression as a 1.0 m
copper(II) chloride solution? Why?
As I understand this question, the idea is that
you have a solution of stuff which you freeze, and
you have discovered that the freezing point of the
solution is lower than that of water. To answer
this question, you really need to understand why
the freezing point of a solution will be lowered.
The first thing to think about is: does this
affect have anything to do with the interaction
energy between the molecules in solution? If
not, this effect must be entirely due to the
The only difference between your two solutions
is that sulfate has been replaced with chloride.
So, the question is, what effect does this have
on the interaction energy between the dissociated
particles in solution? What effect does this have
on the entropy?
From this, you should be able to work out the
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