1. ACID-BASE EQUILIBRIA AP CHEM CH 15

2. The Common Ion Effect The shift in equilibrium that occurs because of the addition of an ion already involved in the equilibrium reaction Le Chatelier’s Principle Calculate the %-dissociation of 1.0M HF Calculate the %-dissociation of a solution that is 1.0M HF and 1.0M NaF (K a =7.2x10 -4 )

3. BUFFERS Resist change in pH when additional H+ or OH- are added. An application of the common ion effect Consist of a weak acid and its salt OR a weak base and its salt THIS IS NOT A NEW TYPE OF PROBLEM, BUT AN APPLICATION OF STUFF YOU ALREADY KNOW

4. Calculate the pH of a buffered solution containing 0.50M acetic acid and 0.50M sodium acetate

5. pH changes Calculate the change in pH that occurs when 0.010 mol solid NaOH is added to 1.0L of water. Calculate the change in pH that occurs when 0.010 mol solid NaOH is added to 1.0L of the buffered solution in the previous problem.

6. How does buffering work? The pH of a buffered solution depends on the ratio of HA to A - If the concentrations of HA and A - are large compared with the amount of acid or base added, the H + concentration will not change The Henderson-Hasselbalch Equation

7. Sample Calcs Find the pH of a solution containing 0.75M lactic acid (K a =1.4x10 -4 ) and 0.25M sodium lactate. Find the pH of a solution containing 0.25M ammonia (K b =1.8x10 -5 ) and 0.40M ammonium chloride

8. Adding strong acid to a buffered solution Calculate the pH of the solution that results when 0.10 mol gaseous HCl is added to 1.0L of the buffered solution of ammonia we just worked with.

9. Buffer Capacity The pH is determined by the ratio of HA to A- The capacity is determined by the magnitude of HA and A- Calculate the change in pH that occurs when 0.010 mol HCl is bubbled through 1.0L of each of the following: – 5.00M acetic acid and 5.00M sodium acetate – 0.050M acetic acid and 0.050M sodium acetate

10. Preparing a buffer Choose the right conjugate pair! A chemist needs a solution at pH 4.30 – Which acid is best? Chloroacetic acid (1.35x10 -3 ) Propanoic acid (1.3x10 -5 ) Benzoic acid (6.4x10 -5 ) Hypochlorous acid (3.5x10 -8 ) – Calculate the ratio required for each system to yield a pH of 4.3.