Question #280624
A 500 mL solution was made with strontium hydroxide. The pH was tested and was measured to be 13.45. How many grams of strontium hydroxide was used to make the solution?
Expert's answer
Strontium Hydroxide ionizes in water to produce the strontium ion and the hydroxide ion. Note that S
r
(
O
H
)
2
is slightly soluble in water.
S
r
(
O
H
)
2
⇌
S
r
2
+
+
2
O
H
−
I
0.1475
M
−
−
C
−
x
+
x
+
2
x
E
0.1475
−
x
x
2
x
K
b
=
[
O
H
−
]
2
[
S
r
2
+
]
[
S
r
(
O
H
)
2
]
K
b
=
(
2
x
)
2
⋅
(
x
)
0.1475
−
x
=
6.5
×
10
−
3
Solve for x
x
=
0.05346
M
[
O
H
−
]
=
2
x
=
2
×
0.05346
=
0.1069
M
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
In any aqueous solution, both ions H
3
O
+
and O
H
−
are present and they must satisfy the following condition:
[
H
3
O
+
]
[
O
H
−
]
=
K
W
[
H
3
O
+
]
[
O
H
−
]
=
1.0
×
10
−
14
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
[
O
H
−
]
=
0.1069
M
( determined)
[
H
3
O
+
]
=
1.0
×
10
−
14
[
O
H
−
]
[
H
3
O
+
]
=
1.0
×
10
−
14
0.1069
[
H
3
O
+
]
=
9.355
−
14
M
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
−
p
H
=
−
log
[
H
3
O
+
]
p
H
=
−
log
[
3.955
−
14
]
p
H
=
13.0290
p
O
H
=
−
log
[
O
H
−
]
p
O
H
=
−
log
[
0.1069
]
p
O
H
=
0.97
