Kw = 1.00 x 10-14
pH = -log [H3O+]
Sometimes rearranging the pH equation is useful to its understanding. Solving for [H3O+],
[H3O+] = 10-pH
Using this equation you can tell quickly that if a solution has an [H3O+] of 10-4, then the pH of the solution is 4.
Another useful tool for beginning students is to look at the [H3O+] values in non-scientific notation. Look over the following table carefully.
|
[H3O+] |
[H3O+] |
pH |
Type of solution |
|
0.1 |
10-1 |
1 |
|
|
0.01 |
10-2 |
2 |
strong acids |
|
0.001 |
10-3 |
3 |
|
|
0.0001 |
10-4 |
4 |
|
|
0.00001 |
10-5 |
5 |
weak acids |
|
0.000001 |
10-6 |
6 |
|
|
0.0000001 |
10-7 |
7 |
neutral |
|
0.00000001 |
10-8 |
8 |
|
|
0.000000001 |
10-9 |
9 |
|
|
0.0000000001 |
10-10 |
10 |
weak bases |
|
0.00000000001 |
10-11 |
11 |
|
|
0.000000000001 |
10-12 |
12 |
strong bases |
|
0.0000000000001 |
10-13 |
13 |
|
|
0.00000000000001 |
10-14 |
14 |
|
Note that as the pH gets larger, the [H3O+] gets smaller. This is often a source of confusion. Look over the powers of 10 in column two and compare them to the values in column one to see the relationship more clearly.
Using the Kw, you can see
what happens to the [
|
[H3O+] |
[H3O+] |
pH |
[ |
[ |
|
1.0 |
100 |
0 |
10-14 |
0.00000000000001 |
|
0.1 |
10-1 |
1 |
10-13 |
0.0000000000001 |
|
0.01 |
10-2 |
2 |
10-12 |
0.000000000001 |
|
0.001 |
10-3 |
3 |
10-11 |
0.00000000001 |
|
0.0001 |
10-4 |
4 |
10-10 |
0.0000000001 |
|
0.00001 |
10-5 |
5 |
10-9 |
0.000000001 |
|
0.000001 |
10-6 |
6 |
10-8 |
0.00000001 |
|
0.0000001 |
10-7 |
7 |
10-7 |
0.0000001 |
|
0.00000001 |
10-8 |
8 |
10-6 |
0.000001 |
|
0.000000001 |
10-9 |
9 |
10-5 |
0.00001 |
|
0.0000000001 |
10-10 |
10 |
10-4 |
0.0001 |
|
0.00000000001 |
10-11 |
11 |
10-3 |
0.001 |
|
0.000000000001 |
10-12 |
12 |
10-2 |
0.01 |
|
0.0000000000001 |
10-13 |
13 |
10-1 |
0.1 |
|
0.00000000000001 |
10-14 |
14 |
100 |
1.0 |