The pH of an alkaline solution is 10. What is its pOH?
Answers
Answer:
Consider the autoionization reaction of water with itself. This is an equilibrium that is heavily favored towards water, but nevertheless, it occurs.
2
H
2
O
(
l
)
⇌
H
3
O
+
(
a
q
)
+
OH
−
(
a
q
)
Or, this is the same thing:
H
2
O
(
l
)
⇌
H
+
(
a
q
)
+
OH
−
(
a
q
)
From this, we have the equilibrium constant known as the autoionization constant,
K
w
, equal to
10
−
14
. Thus, we have the following equation (remember to not use a liquid in the expression):
K
w
=
[
H
+
]
[
OH
−
]
=
10
−
14
where
[
H
+
]
is the concentration of hydrogen ion and
[
OH
−
]
is the concentration of hydroxide polyatomic ion in
M
.
Next, let's take the base-10 negative logarithm of this. Recall that
−
log
(
K
w
)
=
pK
w
. We then get:
pK
w
=
14
=
−
log
(
[
H
+
]
[
OH
−
]
)
=
−
log
(
[
H
+
]
)
+
(
−
log
(
[
OH
−
]
)
)
Similar to what happened with
−
log
(
K
w
)
=
pK
w
,
−
log
(
[
H
+
]
)
=
pH
and
−
log
(
[
OH
−
]
)
=
pOH
. Thus, we have:
pK
w
=
pH
+
pOH
=
14
So, once you know this equation, what you get is:
pH
=
14
−
pOH
=
14
−
10
=
4
Acidity is basically (pun?) when the
pH
is less than
7
. We know that
4
<
7
, thus the solution is acidic. The overall spectrum is:
pH
<
7
→
acidic
pH
=
7
→
neutral
pH
>
7
→
basic
Explanation:
The pOH of an alkaline solution is 4 if the pH is 10.
- The pH of a solution can be related to the pOH. The pOH scale is similar to the pH scale in that a pOH of 7 is indicative of a neutral solution.
- A basic solution has a pOH less than 7, while an acidic solution has a pOH greater than 7.
- The pOH can be found by the simple formula: