pH =
log
1
=
-log [H
+
]
[H
+
]
From this equation we substitute 1 x 10
-7
for [H
+
] and we get
pH =
log
1
=
log [1 x 10
7
] = log1 + log7 =
7
1 x 10
-7
Thus, the pH of water is 7.