10. Calculate the pH of a 1.5 x 10-7 M solution of Sr(OH)2, a strong base.

Ionization equilibrium: H2O (l) H+ (aq) + OH- (aq)

I.C.E. table:

H2O (l) H+ (aq) OH- (aq)
INITIAL
-
0M
3.0x10-7M
CHANGE
-
+xM
+xM
EQUILIBRIUM
-
xM
(3.0x10-7+x)M

Now substitute the equilibrium concentrations into the Kw expression! Which of the following represents the correct substitution?

a) Kw = 1.0 x 10-14 = {x2}
b) Kw = 1.0 x 10-14 = {(x)(3.0 x 10-7+x)}
c) Kw = 1.0 x 10-14 = 1 / {(x)(3.0 x 10-7+x)}
d) Kw = 1.0 x 10-14 = x / {3.0 x 10-7+x}