Hi again Babcock_Hall,

OK, here's my stab at it:

1) First things first, converting Molar to moles for each compound involved.

1a) 0.1L*0.2mol/L => 0.02mol unknown compound

1b) 0.04L*0.2mol/L => 0.0008mol HCl

2) Find original mol of base::acid

pH=pKa+log(base/acid)

8.2=8.8+log(base/acid)

10^-0.6=base/acid

0.25=base/acid

Therefore, there are 0.004mol of the base and 0.016mol of the acid ORIGINALLY.

3) Find change in mol of base::acid

Change is from 1b) above, i.e. 0.0008 mol acid added, 0.0008 mol base subtracted. The final amounts of base and acid are 0.0032 mol and 0.0168 mol, respectively.

4) I just thought of this now... maybe you can confirm if I'm correct? I think I need to plug in the new base::acid amounts and the new pH, then calculate the new pKa...right? (maybe?)

6.2=pKa+log(0.0032/0.0168)

6.2=pKa+.72

5.5=pKa

If 4) above is correct, could you explain why? I just guessed. I don't understand the reasoning behind it, it just seemed to work with the numbers I had up until that point. Thanks!