Estimation of pH - Background Information

pH



The [H3O+] of a solution is often expressed as a pH. pH is defined as the negative logarithm of [H3O+]. The pH at a number of [H3O+] values is shown in the table below.

pH at Various Hydronium Ion ([H3O+]) Concentrations
[H3O+] pH [H3O+] pH
1 x 10-1 1 1 x 10-8 8
1 x 10-2 2 1 x 10-9 9
1 x 10-3 3 1 x 10-10 10
1 x 10-4 4 1 x 10-11 11
1 x 10-5 5 1 x 10-12 12
1 x 10-6 6 1 x 10-13 13
1 x 10-7 7 1 x 10-14 14


Notice that for a neutral solution, where the [H3O+] = 1 x 10-7, the pH is seven. If the [H3O+] increases, the pH decreases. If the [H3O+] decreases, the pH increases. Solutions that have a pH less than seven are acidic and those with a pH greater than seven are basic.

The pH of a solution can be determined in several ways:

using acid-base indicators

using pH paper

using a pH meter



Optional: Read some additional detail about acids, about bases or about pH.


This completes the background material. Proceed to the prelab.


introduction background prelab experiment postlab