Question

A 0.15M solution of weak triprotic acid is adjusted (base added) so that the pH is 9.27(you can assume minimal volume change). The triprotic acid(H3A) has the following acid ionization constants: Kal=1.0*e-3, ka2=1*e-8,ka3=1*e-12. which species given below is present in the highest concentration in this pH 9.27 solution?

Answer 1

A pH of 9.27 is between the 1st and 2nd equivalence points; therefore, the solution is a mixture of H2A^- and HA^2-.
I would use the Henderson-Hasselbalch equation and solve for the Base/Acid ratio. That should tell you which species predominates.

Answer 2

1)H3O+
2)H2A-
3)HA-2
4)A-3
THAT'S the answer choices I think is HA-2, IT IS RIGHT

Answer 3

I agree.