11. Calculate the pH of a 1.5 x 10
-7
M solution of Sr(OH)
2
, a strong base.
Ionization equilibrium:
H
2
O (l)
H
+
(aq) + OH
-
(aq)
I.C.E. table:
H
2
O (l)
H
+
(aq)
OH
-
(aq)
INITIAL
-
0M
3.0x10
-7
M
CHANGE
-
+xM
+xM
EQUILIBRIUM
-
xM
(3.0x10
-7
+x)M
K
w
=1.0 x
10
-14
= {(x)(3.0x10
-7
+x)}
We can solve for
x
to get 3.03 x
10
-3
M =
[ H
+
]
.
What is the final step?
a) find the [OH
-
] by substituting this [ H
+
] into either the K
w
expression or the expression for the equilibrium [OH
-
]
b) find the pH by pH = - log
(K
a
)
c) find the pH by pH = - log
[ H
+
]
d) find the pH by pH = - log
{K
w
/ [ H
+
]}
