Ch.15: Acid-Base and pH Part 1

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

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.

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 1 mol 1 mol Therefore, whatever the molarity of the solution, that is the molarity of the ions produced.

[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

The pH Scale