1. Acid-Base Equilibria
Chapter 16

2. Models of Acid-Base Behavior

3. 1. Arrhenius Acids and Bases
Arrhenius Acid –produce H+
HCl(aq)  H+ + Cl-
Arrhenius Base- produce OH-
NaOH(aq)  Na+ + OH-

4. 2. Bronsted-Lowry Acids and Bases
B-L acid-base rxns involve a transfer of a proton (H+)
B-L Acid = donates H+
B-L Base = accepts H+

5. 2. Bronsted-Lowry Acids and Bases
HCl + NH3  Cl- + NH4+
HCl + H2O  H3O+ + Cl-
H2O + NH3  NH4+ +OH-
Amphiprotic – a substance that can be an acid or base

6. 2. Bronsted-Lowry Acids and Bases
conjugate acid-base pairs differ only by a proton

7. Sample Exercise 16.1 Identifying Conjugate Acids and Bases
What is the conjugate base of each of the following acids: HClO4, H2S, PH4+, HCO3–?
(b) What is the conjugate acid of each of the following bases: CN-, SO42–, H2O, HCO3– ?

8. Sample Exercise 16.2 Writing Equations for Proton-Transfer Reactions
The hydrogen sulfite ion (HSO3–) is amphiprotic.
Write an equation for the reaction of HSO3– with water, in which the ion acts as an acid
Write an equation for the reaction of HSO3– with water, in which the ion acts as a base.

9. The Autoionization of Water
acid base
The ion product of water, Kw=[H3O+][OH-] = 1x10-14

10. The Autoionization of Water
[H+] =[OH-] is neutral
[H+] > [OH-] is acidic
[H+] < [OH-] is basic

11. Sample Exercise 16.5 Calculating [H+] from [OH-]
Calculate the concentration of H+(aq) in
(a) a solution in which [OH–] is M,
(b) a solution in which [OH–] is 1.8 ×10–9 M .

12. 3. Lewis Acids and Bases
A lewis acid is an electron pair acceptor
A lewis base is an electron pair donor
Doesn’t pertain to just H+

13. 3. Lewis Acids and Bases

14. The pH Scale
Acid Neutral Basic

15. The pH Scale --- key equations
pH = -log[H+]
[H+]=10-pH
The pH decreases as [H+] increases
pOH = -log[OH-]
[OH-]=10-pOH
pH + pOH = 14

16. The pH Scale

18. The pH Scale Measuring pH 1. pH meters
2. Titration and Acid-Base Indicators-colored substance that can exist as an acid or base, each having its own color

21. pH meter simulation
Acid-Base Solutions
pH Scale

22. Sample Exercise 16.7 Calculating [H+] from pH
A sample of freshly pressed apple juice has a pH of Calculate [H+], [OH-], and pOH.

23. Strong Acids and Bases
7 strong acids ???
Strong acids are strong electrolytes and completely ionize in aqueous soln

24. Strong Acids and Bases
In aqueous solutions of strong acids, the [H+] equals the original concentration of acid, calculate the pH from [H+]

25. Sample Exercise 16.8 Calculating the pH of a Strong Acid
What is the pH of a M solution of HClO4?

26. Strong Acids and Bases
Strong bases ???
Strong bases are strong electrolytes and completely ionize in aqueous soln

27. Strong Acids and Bases
In aqueous solns of strong bases, the [OH-] depends on the coefficient of the equation
Calculate pH from pOH

28. Sample Exercise 16.9 Calculating the pH of a Strong Base
What is the pH of
(a) a M solution of NaOH
(b) a M solution of Ca(OH)2?

29. Weak Acids
weak acids are partially ionized which is represented as an equilibrium reaction
HA + H2O  H3O+ + A-
or HA H+ + A-

30. Weak Acids
Ka is the acid-dissociation constant and the magnitude of it indicates the tendency of the acid to ionize.
The larger the Ka, the stronger the acid.

31. Weak Acids
It is possible to calculate Ka from pH

32. Sample Exercise 16.10 Calculating Ka from Measured pH
A student prepared a 0.10 M solution of formic acid (HCOOH) and measured its pH. The pH at 25 ºC was found to be Calculate Ka for formic acid at this temperature.

33. Weak Acids
Or you can calculate pH from Ka
What is the pH of 0.30M HC2H3O2 ? (Ka = 1.8x10-5)

34. Sample Exercise 16.11 Calculating Percent Ionization
A 0.10 M solution of formic acid (HCOOH) contains 4.2 × 10–3 M H+(aq) . Calculate the percentage of the acid that is ionized.

35. Warm up: Calculate the pH of a 0.20 M solution
Sample Exercise Using Ka to Calculate pH
Calculate the pH of a 0.20 M solution
of HCN. (Ka = 4.9x10-10.)
(2) Calculate the pH of 0.20M HNO3.

36. Sample Exercise 16.13 Using Ka to Calculate Percent Ionization
Calculate the percentage of HF molecules ionized in (a) a 0.10 M HF solution, (b) a M HF solution

37. Weak Acids Polyprotic Acids have more than one ionizable H atom
It is always easier to remove the first proton from a polyprotic acid than the second
Ex. H2CO3

38. Weak Bases
Weak bases react with water by taking away a proton forming the conjugate acid of the base and OH- ions
B + H2O  BH+ + OH-

39. Weak Bases Types of Weak Bases
1. Neutral substances that have an atom with a nonbonding pair of electrons that can serve as a proton acceptor (substances w/N)
2. Anions of weak acids ; conjugate base of weak acids

40. Weak Bases

41. Weak Bases

42. Sample Exercise 16.15 Using Kb to Calculate OH¯
Calculate the pH of a 0.15 M solution of NH3.
Kb = 1.8x 10-5

43. Relationship between Ka and Kb
Ka x Kb=Kw = 1.0 x 10-14
pKa = -logKa
pKb=-log Kb
pKa + pKb = pKw = at 25oC

44. Relationship between Ka and Kb
As the strength of an acid increases (larger Ka), the strength of its conjugate base decreases (smaller Kb)
Or vice versa

45. Sample Exercise 16.17 Calculating Ka or Kb for a Conjugate Acid-Base Pair
Calculate (a) the base-dissociation constant, Kb, for the fluoride ion (F–); (b) the acid dissociation constant, Ka, for the ammonium ion (NH4+).

46. Acid-Base Properties of Salt Solutions
salt solutions can be acidic, neutral, or basic
the pH of a salt solution can be predicted by the ions that make up the salt

47. Acid-Base Properties of Salt Solutions
General Rules
1. An anion that is the conjugate base of a SA will not affect the pH of a solution (Cl-)

48. Acid-Base Properties of Salt Solutions
2. An anion that is the conjugate base of a WA will increase the pH (CN-)

49. Acid-Base Properties of Salt Solutions
3. A cation of a SB will not affect pH (Na+)

50. Acid-Base Properties of Salt Solutions
4. A cation that is the conjugate acid of a WB will cause a decrease in pH (NH4+)

51. Acid-Base Properties of Salt Solutions
5. With the exception of ions of group 1A and heavier members of 2A, metal ions will cause a decrease in pH

52. Acid-Base Properties of Salt Solutions
6. When a soln contains both the conj. base of a WA and the conj. acid of a WB, the ion with the largest Keq will have the greatest influence on pH

53. Sample Exercise 16.18 Determining Whether Salt Solutions Are Acidic, Basic, or Neutral
Determine whether aqueous solutions of each of the following salts will be acidic, basic, or neutral:
(a) Ba(CH3COO)2
(b) NH4Cl
(c) CH3NH3Br
(d) KNO3
(e) Al(ClO4)3.

54. Practice Exercise 16.18 Determining Whether Salt Solutions Are Acidic, Basic, or Neutral
In each of the following, indicate which salt in each of the following pairs will form the more acidic (or less basic) M solution:
NaNO3 or Fe(NO3)3
KBr or KBrO;
CH3NH3Cl or BaCl2
NH4NO2 or NH4NO3.

55. Acid-Base Behavior and Chemical Structure
Acidity increases with stronger attractions for central atoms electron pairs

56. Acid-Base Behavior and Chemical Structure
1. Ionic charge
More positive ions are stronger acids
Na+ < Ca2+ < Al3+
Negative ions are weaker acids
PO43- < HPO42- < H2PO4- < H3PO4

57. Acid-Base Behavior and Chemical Structure
2. Oxidation Number
For similar formulas, greater oxidation number, the stronger the acid
HClO < HClO2 < HClO3 < HClO4
H2SO3 < H2SO4

58. Acid-Base Behavior and Chemical Structure
3. Electronegativity
For similar formulas with different central atoms, greater electronegativity, stronger acid
H2CO3 < H2SO3 < HNO3

59. Titration simulation