1. Drill: Determine the pH of 0.25 M HZ. K aHZ = 2.5 x 10 -7

2. Buffer Solutions

3. Buffer Solution A solution that resists changes in pH

4. Buffer Solution Made from the combination of a weak acid & its salt

5. Buffer Solution Made from the combination of a weak base & its salt

6. Buffer Examples Mix acetic acid & sodium acetate Mix ammonia & ammonium chloride

7. Buffer Solution A buffer solution works best when the acid to salt ratio is 1 : 1

8. Buffer Solution A buffer solution works best when the base to salt ratio is 1 : 1

9. Buffer Solution The buffering capacity of a solution works best when the pH is near the pK a

10. pK a or pK b pK a = - log K a pK b = - log K b

11. Buffer Problems Calculate the pH of a solution containing 0.10 M HAc in 0.10 M NaAc: K a = 1.8 x 10 -5

12. Buffer Problems Calculate the pH of 0.10 M NH 3 in 0.20 M NH 4 NO 3 : K b = 1.8 x 10 -5

13. Buffer Problems Calculate the pH of a solution containing 0.10 M HBz in 0.20 M NaBz: K a = 6.4 x 10 -5

14. Buffer Problems Calculate the pH of a solution containing 0.50 M HQ in 0.10 M NaQ: K a = 4.0 x 10 -5

15. Drill Calculate the pH of a solution containing 0.30 M HZ in 0.10 M NaZ: K a = 3.0 x 10 -5

16. Lab Requirements To make accurate measurements, we must have solutions with accurately measured concentrations

17. Standard Solution A solution with known concentration 2.004 M HCl

18. STD Problems Calculate the mass of KHP (MW = 204.23) required to make 1.0 L of 0.100 M KHP

19. Henderson- Hasselbach Eq [A - ] [HA] pH = pK a + log

20. Henderson- Hasselbach Eq [B + ] [B] pOH = pK b + log

21. Buffer Problems Calculate the salt to acid ratio to make a buffer solution with pH = 5.0 K a for HBZ = 2.0 x 10 -5

22. Buffer Problems Calculate the salt to base ratio to make a buffer solution with pH = 9.48 K b for MOH = 2.0 x 10 -5

23. Calculate the HCO 3 - to H 2 CO 3 ratio in blood with pH = 7.40 K a1 for H2CO3 = 4.4 x 10 -7

24. 150 ml of 0.10 M NaOH is added to 100.0 ml of 0.10 M H 2 CO 3. Calculate all. K a1 for H2CO3 = 4.4 x 10 -7 K a2 for H2CO3 = 4.7 x 10 -11