Chapter 16 Notes1 Chapter 16 Aqueous Equilibria: Applications 1. neutralization reactions: K large, ~100% completion due to formation of water; salts can be neutral, basic, or acidic 2. common ion effect; buffers: common ion reduces % ionization of weak acid; buffers: neutralization plus weak acid/base equilibrium 3. titrations: acid (base) is systematically and quantitatively added to base (acid) in order to determine the concentration of the base (acid)

Chapter 16 Notes2 strong acid - strong base: 1. examples: HCl with NaOH; HClO 4 with KOH; NaOH with HNO 3 2. salts: all neutral therefore NO acid-base equilibria; the chemistry is all neutralization 3. the pH titration curve: plot pH (y-axis) vs. volume added base (x-axis)

Chapter 16 Notes3 a. b. c. a. before adding base b. halfway to equivalence point c. 1 ml before equivalence point d. e. f. d. equivalence point e. 1 ml after equivalence point (f. beyond equivalence point)

Chapter 16 Notes4 example: 40.0 ml of 0.10 M HCl is titrated with 0.10 M NaOH; calculate pH at points a-f. Hints: Don’t forget dilution! Calculate pH as though adding base from the beginning. What volume NaOH is required to reach equivalence point? a. before adding base pH=-log[H 1+ ]=-log(0.10)=1.00 b. halfway to equivalence point: 20.0 ml added base (total) chemistry : H 1+ + OH 1-  H 2 O c. 1 ml before equivalence point: 39.0 ml added base (total) chemistry :

Chapter 16 Notes5 d. equivalence point: 40.0 ml added base (total) chemistry : e. 1 ml after equivalence point (total) chemistry : f. beyond equivalence point (total) chemistry :

Chapter 16 Notes6 note rapid change in pH near the equivalence point

7 a. c. b. buffer a. before adding base b. halfway to equivalence point c. 1 ml before equivalence point e. d. f. d. equivalence point e. 1 ml after equivalence point (f. beyond equivalence point)

Chapter 16 Notes8 a. before adding base: pH of a weak acid (equilibrium) chemistry: b. halfway to equivalence point: chemistry: c. 1 ml before equivalence point: chemistry:

Chapter 16 Notes9 d. equivalence point: chemistry: [pH of a conjugate base of a weak acid; look up K b or calculate using K b =K w /K a ] e. 1 ml after equivalence point: chemistry: [pH of a strong base (OH 1- contribution from conjugate base is insignificant)] (f. beyond equivalence point: see e.)

Chapter 16 Notes10 Note change in pH near equivalence point. Contrast strong-strong and strong-weak: what are the 2 most important differences?

Chapter 16 Notes11 Figure 16.7

Chapter 16 Notes12 Figure 16.8

Chapter 16 Notes13 Figure 16.9: Titration of weak base with strong acid buffer: use base form of H-H equation

Chapter 16 Notes14 Figure 16.9: Titration of polyprotic weak acid with strong base pH=(pK a1 +pK a2 )/2