Converting between pH and [H3O+(aq)]
To go from pH to [H3O+(aq)]:
[H3O+ (aq)] = 10 –pH mol/L
Sample:
Calculate the [H3O+(aq)] of a solution with a pH of 9.32.
[H3O+(aq)] =
10-9.32 mol/L
On calculator:
[2nd][LOG][ (-) ][ 9 ][ . ][ 3 ][ 2 ][ = ]
[H3O+(aq)] =
4.8 x 10-10 mol/L
Practice!
pH
2.66
10.9
5.4
7.7
8.1
9.0
12.22
3.4
10.167
13.9
0.2
[H3O+(aq)]
2.2 x 10-3 mol/L
1.3 x 10-11 mol/L
4.0 x 10-6 mol/L
2.0 x 10-8 mol/L
7.9 x 10-9 mol/L
1 x 10-9 mol/L
6.0 x 10-13 mol/L
4.0 x 10-4 mol/L
6.81 x 10-11 mol/L
1.3 x 10-14 mol/L
6.3 x 10-1 mol/L
To go from [H3O+(aq)] to pH:
pH = -log( [H3O+ (aq)] )
Sample:
Calculate the pH of a solution with a [H3O+ (aq)] of 1.4 x 10-9 mol/L.
pH =
-log( 1.4 x 10-9 mol/L )
On calculator:
[(-)][LOG][ 1 ][ . ][ 4 ][ 2nd ][ , ][ (-) ]  [ 9 ]
Alternate method:
[(-)][LOG][ 1 ][ . ][ 4 ][ x ][ 1 ][ 0 ]  [ ^ ] [ (-) ][ 9 ]
pH =
8.85
Practice!
pH
4.64
10.03
6.11
1.89
10.1
7.00
8.066
2.35
2.35
0.036 (or 3.6 x 10-2)
12.5
[H3O+(aq)]
2.3 x 10-5 mol/L
9.4 x 10-11 mol/L
7.7 x 10-7 mol/L
1.3 x 10-2 mol/L
7.9 x 10-11 mol/L
1.0 x 10-7 mol/L
8.59 x 10-9 mol/L
4.5 x 10-3 mol/L
4.47 x 10-3 mol/L
9.2 x 10-1 mol/L
3.2 x 10-13 mol/L