Ionization of Water CHEM 7784 Biochemistry Professor Bensley

Chapter 2.2 Ionization of Water  How weak acids and bases behave in water Today’s Objective: to understand

Ionization of Water H 2 O H + + OH -   Let’s do the “Proton Hop”

Ionization of Water H H 2 0H 3 O + + OH - K eq = [H + ] [OH - ] [H 2 O] H 2 0 H + + OH - K eq =1.8 X M [H 2 O] = 55.5 M [H 2 O] K eq = [H + ] [OH - ] (1.8 X M)(55.5 M ) = [H + ] [OH - ] 1.0 X M 2 = [H + ] [OH - ] = K w If [H + ]=[OH - ] then [H + ] = 1.0 X 10 -7

What is pH? pH = -log[H + ]

Dissociation of Weak Electrolytes: Principle

Dissociation of Weak Electrolytes: Example What is the final pH of a solution when 0.1 moles of acetic acid is adjusted to 1 L of water? 0.1 – x x x

Dissociation of Weak Electrolytes: Simplification 0.1 – x x x 0.1 x x

pK a measures acidity pK a = -log K a (strong acid  large K a  small pK a )