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<big><font size="2"><big>Students often ask many questions about
common-ion problems,<br>
mainly how we can do them by treating them as if we add the
substances<br>
simultaneously to the beaker (when in reality that's not what
we are<br>
doing). I've attached an explanation as to why we can do
these problems<br>
as I did in class. I did the problem first as it would be
done following what<br>
is actually physically occurring (adding the common ion to an
existing<br>
equilibrium causing it to shift back to the left). I quickly
showed this page<br>
and actually told everyone to not try to write down what was
on that page.<br>
Next I did it assuming we add everything simultaneously to the
beaker.<br>
You will see we get the same results but the 2nd way is a
whole lot easier.<br>
<br>
Dr. Zellmer</big></font></big>
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