[ixi]

i have to find the buffer capacity. the pH region is 4-6. the pka is 4.7. the initial pH is 3

3=-log[H+]
[H+]=[A-]=0.001

using this equation

Ka = [H+][A-] / [HA]-[H+]
i found HA to be 0.052

this is where i get lost
i want to find the [A-] at pH 6
using equation-->
ph=pka + log base/acid

wouldn it be-
6=4.7+ log [A-]/[0.052]  ?

help please i have a test tomorrow!!!

[AWK]

Borek has a good site on this subject:
http://www.chembuddy.com/?left=pH-calculation&right=pH-buffer-capacity