Posted by Amanda on .
I don't get this at all.
A beaker with 105mL of an acetic acid buffer with a pH of 5.00 is sitting on a bench top. The total molarity of acid and conjugate base in this buffer is 0.100 M. A student adds 8.40 mL of a 0.470 M HCl solution to the beaker. How much will the pH change? The pKa of acetic acid is 4.760.

Chemistry 
DrBob222,
pH = pKa + log(b/a)
5.00 = 4.74 + log b/a
solve for b/a which has two unknowns. The second equation you need is
b + a = 0.1M
Solve the two equations simultaneously for CH3COOH and CH3COO^ and that's the first part of the problem. Post back with this work if you need help finishing with the second part. 
Chemistry 
bob,
need more help

Chemistry 
bob,
need more help