Answer:
pH
=
10.66
Explanation:
For pure water at
25
∘
C
, the concentration of hydronium ions,
H
3
O
+
, is equal to the concentration of hydroxide ions,
OH
−
.
More specifically, water undergoes a self-ionization reaction that results in the formation of equal concentrations of hydronium and hydroxide anions.
2
H
2
O
(l]
⇌
H
3
O
+
(aq]
+
OH
−
(aq]
At room temperature, the self-ionization constant of water is equal to
K
W
=
[
H
3
O
+
]
⋅
[
OH
−
]
=
10
−
14
This means that neutral water at this temperature will have
[
H
3
O
+
]
=
[
OH
−
]
=
10
−
7
M
As you know, pH and pOH are defined as
pH
=
−
log
(
[
H
3
O
+
]
)
pOH
=
−
log
(
[
OH
−
]
)
and have the following relationship
pH
+
pOH
=
14
In your case, the concentration of hydroxide ions is bigger than
10
−
7
M
, which tells you that you're dealing with a basic solution and that you can expect the pH of the water to be higher than
7
.
A pH equal to
7
is characteristic of a neutral aqueous solution at room temperature.
So, you can use the given concentration of hydroxide ions to determine the pOH of the solution first
pOH
=
−
log
(
4.62
⋅
10
−
4
)
=
3.34
This means that the solution's pH will be
pH
=
14
−
pOH
pH
=
14
−
3.34
=
10.66
Indeed, the pH is higher than
7
, which confirms that you're dealing with a basic solution.
