posted by Jaron .
A 9.00 M solution of a weak acid, HA, has a pH of 1.30
1.) calculate [A-] at equilibrium
2.) calculate [HA] at equilibrium
Use pH to get (H^+).
Ka = (H^+)(A^-)/(HA)
(A^-) = (H^+).
(HA) = 9
Plug and chug.
Post your work if you get stuck.