The
acid dissociation constant or Ka is a value used to measure the strength of a
specific acid in solution. For a general dissociation of an acid solution,
HA = H+ + A-
we express Ka as follows:
Ka = [H+] [A-] / [HA]
Where the terms represents the concentrations of
the acid and the ions. Assuming that the weak acid in the problem is HA, we
first calculate for the concentration of H+ from the pH.
pH = - log [H+]
3.00 = - log [H+]
[H+] = 0.001 M
By the ICE table, we can calculate the
equilibrium concentrations,
HA
= H+
+ A-
I 0.100 0
0
C -x
+x
+x
--------------------------------------------------
E 0.1 - 0.001 0.001 0.001
Ka = (0.001) (0.001) / .099
Ka =
1.0101x10^-5
