what is the acid dissociation constant of a weak acid if a concentration of 0.3 M gives a hydrogen ion concentration of 0.001M?

Question

how do i do this??? i know you use the ka thing.

Answer 1

You don't USE the Ka thing, you SOLVE for the ka thing. Basically you have
HA ==> H^+ + A^-
Ka = (H^+)(A^-)/(HA) = Ka.
You know (H^+) and (A^-). (HA) = 0.3-0.001. Substitute and solve for Ka.