costruct the ICE table
no need to cinsider H2O concentration since it is very large
          Â
HA +Â Â Â Â Â Â Â Â
H2OÂ Â Â Â Â Â
<----->Â Â Â Â Â H3O+ + A-
IÂ Â Â Â Â Â Â Â Â Â Â
0.11Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â
0Â Â Â Â Â Â Â Â Â Â Â Â Â
0
CÂ Â Â Â Â Â Â Â Â Â
-x                                            Â
+x          Â
+x
EÂ Â Â Â Â Â Â Â Â Â Â
0.11-x                                    Â
+x            Â
+x
write the disociation expression
Ka = [H3O+][A-] / [HA]
3.8 × 10-6 = [x] [x] / [0.11-x]
3.8 × 10-6 = x2 / [0.11-x]
x2 + 3.8 × 10-6x - 0.418 * 10-6
= 0
solve the quadratic equation
x = 0.000644 = [H3O+]
pH = -log[H3O+]
= -log [0.000644]
= 3.19
