Questions about Ch 13 EOC exercises

[Zellmer, Robert]

I always receive a few questions about the same end-of-chapter exercises.
Here's partial answers to those questions to get you started on them if
you haven't tried them or are still having problems with them. This
seemed to be most peoples' problems with them, not knowing how
to start them.

Remember, the solutions manual with the answers and explanations
to every single EOC exercise is on Carmen.  You'll find the link at the
"Textbook End-of-Chapter Exercises and Solutions Manuals" module.

13.57:
This is about an alloy of 80% Cu and 20% Zn.  The primary question
was how to start this.  I would say to do this how I suggested.  You
have a solid solution.  You're given % composition.  Assume 100 g
of soln (metal).  That means you have 80 g Cu and 20 g Zn.  This
is what you would have done in 1210 to determine an empirical formula.
Then use the density of the soln (metal) to convert 100 g son to volume
of soln.  By the way, 1 m3 = 103 L (similar to 1 cm3 = 1 mL).


13.101
This question is a conc. conversion question.  You're given a 1.80 M LiBr soln
in the solvent acetonitrile (CH3CN) and the density of the soln. You're then
asked to convert this to molality, mole fraction of LiBr and mass % (of CH3CN).

I approached this type of problem in class by listing what the given conc means
first and then assuming what's in the denominator,

                             1.80 mol LiBr
    1.80 M LiBr =   -------------------
                                  1 L soln

Assume you have a beaker with 1 L soln (what's in the denominator). That then
also gives you what's in the numerator, 1.80 mol LiBr.

Then for each conc. you're trying to get write down it's definition and then
determine how to get to that conc. unit based on what you have.

Don't forget, from molarity to any of the others (and vice versa) you will need
density of the soln to convert from L soln to mass of soln (or vice versa).

Hopefully, this helps with any lingering questions.

Dr. Zellmer
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