Section 17.7 - redux

[Robert Zellmer]

I sent out an e-mail about this previously but a couple of people
have asked me about it concerning the upcoming midterm.

Section 17.7 and question pertaining to the flow chart and
qualitative analysis was only very briefly covered in class and
won't be directly covered on the exam. However, you should
read this section and there were a couple of questions included
in homework. There's a sample integrative exercise at the end
of this section you should be able to do it w/o reading the material
in this section.

I told people to look at Section 17.7 because it gives you
some idea and a physical application of the precipitation (Ksp)
stuff you were learning in sections 17.4-17.6.

For instance, Figure 17.23 (flow chart) you can see
Ag+, Pb^2+, and Hg2^2+ precipitate easily with the addition of
HCl (they form the associated chlorides).  This makes sense
since we saw the corresponding chlorides have small Ksp values,
meaning they aren't very soluble.  By the way, you learned this in
1210 when you went over the solubility rules.

If you look all the way at the bottom of the flowchart you will see
group 2A cations.  They don't form insoluble compounds with
chloride so they don't react.  However, they do form phosphates
which are insoluble (actually most phosphates are insoluble except
those of group 1A cations and NH4+).

The flowchart is effectively using selective precipitation to separate
the cations so it might help for you to read through it even though there
won't be specific questions over the qualitative analysis or flowchart.

You may also find it useful to review section 4.2, particularly the info
on pages 120-121 (12th ed.)   This is the general solubility guidelines
you learned before you knew about Ksp.


Dr. Zellmer
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