Quiz 7, question 7

[Zellmer, Robert]

I've received a number of e-mails about #7 on Quiz 7.  People are falling just
outside the margin of error.

I take try really hard to make sure the margin of error is big enough to account

for differences in how a problem is done.  I know for a fact from past experiences

students can get answers which are close by doing things incorrectly, especially
for these types of problems dealing with pH for buffers and titrations.

I've already had two students who were just outside the margin of error who
e-mailed me about it.  However, when I saw their work they both had made
a mistake.  The mistake was such that it didn't affect the pH by much but just
enough to be outside the margin of error.  A small mistake in the conc. of the
HA and A- may not cause large mistakes in pH because of the logarithmic
relationship of the ratio of [A-]/[HA].

Please check your work again, after the midterm.  Then if you still think there's
a problem you will need to e-mail your work.  I can't determine if there is a
mistake in the question or if maybe I needed to make the margin of error a little
bigger w/o seeing your work.  If you didn't save your work I won't be able to do
anything.

Dr. Zellmer
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