1. Ch.15: Acid-Base and pH
Part 1

2. Self-Ionization of Water
Pure water is a VERY weak electrolyte
It undergoes self-ionization
H2O (l) + H2O (l) H3O+ (aq) + OH-(aq)
[H3O+] means “hydronium ion concentration in moles per liter”
In water, [H3O+] = 1.0 x 10-7 M and [OH-] = 1.0 x 10-7 M
Ionization constant for water Kw= 1.0 x 10-14

3. Neutral, Acidic, and Basic Solutions
When [H3O+] = [OH-] the solution is neutral.
When [H3O+] is higher than the [OH-], the solution is acidic.
When the [OH-] is higher than the [H3O+], the solution is basic.

4. Calculating [H3O+] and [OH-]
Remember, strong acids and bases are considered completely ionized in aqueous solutions.
NaOH(s) H2O Na+(aq) + OH-(aq)
1 mol mol mol
Therefore, whatever the molarity of the solution, that is the molarity of the ions produced.

5. [H3O+] and [OH-] determine pH and pOH
Most often we express acidity and basicity in terms of pH or pOH.
The pH of a solution is defined by the following equation:
pH = - log [H3O+] [H3O+] = 10-pH
The pOH of a solution is defined by the following equation:
pOH = - log [OH-] [OH-] = 10-pOH
Therefore:
pH + pOH = 14

6. The pH Scale