This document discusses the pH scale and calculations involving pH. It explains that water undergoes self-ionization into hydronium and hydroxide ions. The ionization constant, Kw, is defined as the product of the hydronium and hydroxide concentrations. The document also describes how to calculate pH, pOH, and concentrations from these values, noting that pH + pOH always equals 14 at 25 degrees Celsius.

1. pH
Calculations
Soren Sorensen

2. pH
Scale

3. Self-Ionization of Water
H2O + H2O  H3O+ + OH-
Though pure water is considered a
non-conductor, there is a slight, but
measurable conductivity due to “self-
ionization”

4. Kw – Ionization Constant for Water
In pure water at 25 C:
[H3O+] = 1 x 10-7 mol/L
[OH-] = 1 x 10-7 mol/L
Kw is a constant at 25 C:
Kw = [H3O+][OH-]
Kw = (1 x 10-7)(1 x 10-7) = 1 x 10-14

5. Calculating pH, pOH
pH = -log10(H3O+)
pOH = -log10(OH-)
Relationship between pH and pOH
pH + pOH = 14
Finding [H3O+], [OH-] from pH, pOH
[H3O+] = 10-pH
[OH-] = 10-pOH

6. pH + pOH = 14