EOC buffer questions 17.25 and 17.26

[Zellmer, Robert]

I've received questions about EOC exercises 17.25 and 17.26.  These are
companion problems.  They're about adding the salt of the conjugate base of
a weak acid to a solution of the weak acid to make a buffer system. This is the
same as a common-ion problem (since buffers are special CI problems)

They're not as complicated as you might think from reading the question so don't
make them more complicated than necessary.  Solve for the conc. of the conj. base
using the expression for Ka for the acid, the [acid] and the [H+] you get from the pH.

You can also use the HH eqn and first solve for the ratio of [base]/[acid].  Then
given a volume and conc of acid you can determine how much of it's conj base
has to be added to get the desired pH for the buffer.  You can also be given
the volume and conc of a base and asked to determine how much of the base's
conj. acid has to be added to get the desired pH for the buffer.

I mentioned these two questions in previous e-mail.

Dr. Zellmer
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