1. Chapter 17 Solution Equilibria What is the Common Ion Effect ?

2. What is a common ion? • Examine this solution. • What if I added sodium chloride to this solution at equilibrium? Chloride (Cl-) • Is there a common ion? Would there be an effect on equilibrium?

3. LeChatlier’s Principle • Shifts to counter the disturbance • it would tend to remove the chloride ions by making extra solid lead(II) chloride • SHIFT LEFT

4. Common Ion Effect • A shift in equilibrium position due to the addition of an ion already involved in equilibrium reaction • Important concept in: • Acid-Base Equilibria (may change pH) • Solution Equilibria (may change solubility of salts) • Buffering Capacity • Precipitation Reactions

5. Common Ions and Acid-Base Equilibrium • Consider a general solution of: a weak acid (HA) and a salt (NaA) HA +NaA ?????? The salt dissociates completely into ions like this: NaA(s)  Na +(aq) + A –(aq) • The ionization reaction of the weak acid (HA): HA (aq)  H +(aq) + A –(aq)

6. p. 704 Exercise 17.1 Example: Acid and Common Ions • What is the pH of a sln made by adding 0.30 mol of acetic acid and 0.30 mol of sodium acetate to water to make 1 L of solution? • LIST • THINK REACTION • ICE • CALCULATE