1. Chapter 15

2. Monoprotic Bronsted Acid and Base
Bronsted Acids- able to donate protons in the form of hydrogen ions – protons – H+.
AH A- + H+
HCl  Cl H+
C2H3O2H  C2H3O H+
Bronsted Base- able to accept protons in the form of hydrogen ions or H+.
B- + H BH
NH H+  NH4+
HO H+  H2O

3. Conjugate Acid-Base Pairs
In the reaction of HF and H2O,
HF/F− is one conjugate acid-base pair.
H2O/H3O+ is the other conjugate acid-base pair.
Each pair is related by a loss and gain of H+.

4. Autoionization of Water
H2O(l) H+(aq) + OH-(aq)
Kc =
[H+][OH-]
= Kw
Kw is called the ion-product constant of water.
At 250C
Kw = [H+][OH-] = 1.0 x 10-14
pH = -log [H+]
[H+] = [OH-]
[H+] > [OH-]
[H+] < [OH-]
neutral
acidic
basic
pOH = -log [OH]
pH + pOH = 14

5. Ka and Kb Ka = [H+][A-] [HA] Kb = [AH][OH-] [A-]
HA(aq) H+(aq) + A-(aq)
A-(aq) + H2O(l) AH(aq) + OH-(aq)
Ka =
[H+][A-]
[HA]
Kb =
[AH][OH-]
[A-]
For a acid-base conjugate pair in water:
HA (aq) H+ (aq) + A- (aq) Ka
A- (aq) + H2O (l) OH- (aq) + HA (aq) Kb
H2O (l) H+ (aq) + OH- (aq) Kw
KaKb = Kw

6. Alternative Notation HA(aq) H+(aq) + A-(aq) acid ionization constant
percent ionization =
Ka =
[H+][A-]
[HA]
[H+] at equilibrium
Initial concentration of [HA]
x 100%
acid
strength Ka
Percent ionization =
[H+]
[HA]0
x 100%
Percent ionization:
Strong acids- % ionization is always 100%
Weak acids- % ionization decreases as concentration increases (Ka stays the same!).

7. Chapter 15

8. Polyprotic Bronsted Acid and Base
May yield more than one hydrogen ion per molecule.
Ionize in a stepwise manner; they lose one proton at a time.
H2CO3
HCO H+
acid
conjugate base
acid
HCO3-
CO H+
acid
conjugate base

9. Polyprotic Bronsted Acid and Base
Ionize in a stepwise manner; they lose one proton at a time.
Ka1
Ka2
An ionization constant expression can be written for each
ionization stage.

10. Polyprotic Bronsted Acid and Base
Conjugate base is the acid for the next equilibrium.
The second Ka is “always” smaller than the first.
The acid strength decreases as we go to the species with fewer protons.
Easier to separate H+ and X- than H+ from X2-.
Consequently, two or more equilibrium constant expressions must often be used to calculate the concentrations of species in the acid solution.

11. 15.11
Oxalic acid (H2C2O4) is a poisonous substance used chiefly as a bleaching and cleansing agent (for example, to remove bathtub rings). Calculate the concentrations of all the species present at equilibrium in a 0.10 M solution.
0.10 M
H2C2O4(aq)
H+(aq) +
HC2O4-(aq)
Ka1
HC2O4-(aq)
H+(aq) +
C2O42-(aq)
Ka2
From Table 15.5:
Ka1 = 6.5 x 10-2
Ka2 = 6.1 x 10-5

12. 15.11
Oxalic acid (H2C2O4) is a poisonous substance used chiefly as a bleaching and cleansing agent (for example, to remove bathtub rings). Calculate the concentrations of all the species present at equilibrium in a 0.10 M solution.
H2C2O4(aq)
H+(aq) +
(aq)
Initial (M):
Change (M):
Equilibrium (M):
0.10
0.00
0.00 -x +x +x x x x
= 6.5 x 10-2

13. 15.11 H2C2O4(aq) H+(aq) + (aq) Initial (M): Change (M):
Equilibrium (M):
0.10
0.00
0.00 -x +x +x x x x
= 6.5 x 10-2
x x 10-2x x 10-3 = 0
If > 400
Can we neglect x?
[H2C2O4]0
Ka1
we can neglect x
x = M or M

14. 15.11
Oxalic acid (H2C2O4) is a poisonous substance used chiefly as a bleaching and cleansing agent (for example, to remove bathtub rings). Calculate the concentrations of all the species present at equilibrium in a 0.10 M solution.
H2C2O4(aq)
H+(aq) +
(aq)
Equilibrium (M): x x x
x = M
[H+] = M
[ ] = M
[H2C2O4] = M
the major species are HC2O4-, which acts as the acid in the second stage of ionization to generate more H+, and C2O42-.
HC2O4-(aq)
H+(aq) +
C2O42-(aq)

15. 15.11 For equilibrium 2: [H+] = 0.054 M [ ] = 0.054 M (aq) H+(aq) +
Initial (M):
Change (M):
Equilibrium (M):
0.054
0.054
0.00 -y +y +y y y y
If > 400
[HC2O4-]0
Ka2
we can neglect y
Ka2 = 6.1 x 10-5
y = 6.1 x 10-5 M

16. 15.11
Oxalic acid (H2C2O4) is a poisonous substance used chiefly as a bleaching and cleansing agent (for example, to remove bathtub rings). Calculate the concentrations of all the species present at equilibrium in a 0.10 M solution.
Ka1 = 6.5 x 10-2
0.10 M
H2C2O4(aq)
H+(aq) +
HC2O4-(aq)
HC2O4-(aq)
H+(aq) +
C2O42-(aq)
Ka2 = 6.1 x 10-5
[H2C2O4] = M
[ ] = ( x 10-5) M = M
[H+] = ( x 10-5) M = M
[ ] = 6.1 x 10-5 M
[OH-] = 1.0 x 10-14/0.054 = 1.9 x M

17. Last Example Calculate the pH of a 0.10 M solution of H3PO4.
H3PO4(aq) ⇄ H+(aq) + H2PO4-(aq) Ka1 = 7.5 x 10-3
H2PO4-(aq) ⇄ H+(aq) + HPO42-(aq) Ka2 = 6.2 x 10-8
HPO42-(aq) ⇄ H+(aq) + PO43-(aq) Ka3 = 4.8 x 10-13
Acid strength decreases in the order:
H3PO4 >> H2PO4- >> HPO42-
pH of solution is determined mainly by ionization of H3PO4

18. Conceptual Question

19. Polyprotic Peptides
Polypeptides
Proteins

20. Chapter 15

21. Acid/Base Strength
Some factors that influence acid/base strength (Ka/Kb).
Temperature
Solvent
Acid Structure
Hydrohalic acids
Oxoacids
Carboxylic acids
Ka =
[H+][A-]
[HA]
kfwd =
krev

22. Solvent Dependence [H+][A-] Ka = [HA] HA (aq) H+ (aq) + A- (aq) H2O =
AN =
DCE =
GP = Gas Phase

23. Hydrohalic Acid Strength
The strength of an acid depends on the strength of the X–H bond that is to be broken.
Relative bond strength:
H─F > H─Cl > H─Br > H─I
Relative acid strength:
HI > HBr > HCl > HF
H2Te > H2Se > H2S > H2O (all very weak acids)
For H-X, electronegativity does not play a big role.
7.2 x 10-4
~109
~107 Ka

24. Hydrohalic Acid Strength
H X
H+ + X-
The stronger the bond
The weaker the acid
HF << HCl < HBr < HI
acidity
increases

25. Oxoacid Strength
Oxoacids is an acid that contains oxygen and a central atom Z. Z O H O-
+ H+ d- d+
The O-H bond strength/Ka are dependent on:
electronegativity of Z
oxidation state of Z

26. Cl is more electronegative than Br
Oxoacid Strength
Oxoacids is an acid that contains oxygen and a central atom Z.
If they are from the same group and have the same oxidation number, acid strength increases with increasing electronegativity of Z.
Cl is more electronegative than Br
acidity
increases
HClO3 > HBrO3

27. Acid strength increases as the oxidation number of Z increases.
Oxoacid Strength
Oxoacids having the same central atom (Z) but different numbers of attached groups.
Acid strength increases as the oxidation number of Z increases.
HClO4 > HClO3 > HClO2 > HClO

28. 15.12
Predict the relative strengths of the oxoacids in each of the following groups:
ClOH, BrOH, and IOH
(b) HNO3 and HNO2
ClOH > BrOH > IOH
>
The O-H bond will be easier to break if:
Z is very electronegative or
Z is in a high oxidation state

29. Carboxylic Acid Strength
General structure for a carboxylic acid:
Where R can be anything: H, CH3, Ph, Cl…
The more electrongative R is the stronger the carboxylic acid.
Proximity of the electrongative atom matters.

30. Chapter 15

31. HCl(aq) + NaOH(aq) NaCl(s) + H2O
Acidic and Basic Salts
acid + base salt + water
HCl(aq) + NaOH(aq) NaCl(s) + H2O
Salts are the ionic product of an acid base neutralization reaction. They are composed of related numbers of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge).
XY(s) X+(aq) + Y-(aq)
Soluble salts dissociate completely when dissolved in water.
Ions/salts may acidic, basic or neutral.

32. Acidic and Basic Salts
Acidic Salts are formed from a strong acid and a weak base.
Neutral salts are formed from a strong acid and strong base.
Basic salts are formed from a strong base and a weak acid.
NaCl
NaC2H3O2
NH4Cl
HCl + NaOH
NaCl + H2O
s.a.
s.b.
neutral salt
HC2H3O2 + NaOH
NaC2H3O2 + H2O
w.a.
basic salt
s.b.
NH4OH
NH4Cl
+ H2O
HCl +
s.a.
w.b.
acidic salt

33. Neutral Salts Dissociation and reaction of a neutral salt:
NaCl(aq)  Na+(aq) + Cl-(aq)
Na+(aq) + H2O  NR
Cl- (aq) + H2O  NR
The concentrations of H+ and OH- in NaCl solution are the same as in pure water  solution is neutral.
Neutral salts are typically formed from a strong acid and strong base (which give weak conjugate acid and bases).
Salts containing an alkali metal or alkaline earth metal ion (except Be2+) and the conjugate base of a strong acid (e.g. Cl-, Br-, and NO3-).

34. Basic Salts Dissociation and reaction of a basic salt:
NaNO2(aq)  Na+(aq) + NO2-(aq)
Na+(aq) + H2O  NR
NO2-(aq) + H2O  HNO2(aq) + OH-(aq)
The reaction of NO2- with water causes [OH-] > [H+] and the solution becomes basic.
Basic salts are typically formed from a weak acid and strong base (which gives a weak conjugate acid and a stronger conjugate base).

35. 15.13
Calculate the pH of a 0.15 M solution of sodium acetate (CH3COONa). (Kb of sodium acetate is 5.6 x 10-10)
0.15 M
0.15 M
H2O
CH3COONa (s) Na+ (aq) + CH3COO- (aq)
CH3COO-(aq) + H2O(l) CH3COOH(aq) + OH-(aq)
0.15 M

36. 15.13
Calculate the pH of a 0.15 M solution of sodium acetate (CH3COONa). (Kb of sodium acetate is 5.6 x 10-10)
[CH3COO-] = 0.15 M
CH3COO- (aq)
+ H2O (l)
CH3COOH(aq)
+ OH-(aq)
Initial (M):
Change (M):
Equilibrium (M):
0.15
0.00
0.00 -x +x +x x x x
If > 400
[CH3COO-]0 Kb
we can neglect x

37. 15.13
Calculate the pH of a 0.15 M solution of sodium acetate (CH3COONa). (Kb of sodium acetate is 5.6 x 10-10)
[CH3COO-] = 0.15 M
CH3COO- (aq)
+ H2O (l)
CH3COOH(aq)
+ OH-(aq)
Initial (M):
Change (M):
Equilibrium (M):
0.15
0.00
0.00 -x +x +x
0.15
9.2 x 10-6
9.2 x 10-6
x = 9.2 x 10-6
[OH-] = 9.2 x 10-6 M
pOH = -log (9.2 x 10-6 )
pOH = 5.04
pH =
pH = 8.96

38. Acidic Salts Dissociation and reaction of a neutral salt:
NH4NO3 (aq)  NH4+(aq) + NO3-(aq)
NH4+ (aq) + H2O  NH3(aq) + H3O+(aq)
Cl- (aq) + H2O  NR
The reaction of NH4+ with water causes [H+] > [OH-], and the solution becomes acidic.
Neutral salts are typically formed from a strong acid and weak base (which give weak conjugate acid and bases).
Salts with the conjugate base of a strong acid and small, highly charged metal cations (e.g. Al3+, Cr3+, and Be2+).

39. Hydrated Metal Ions
Hydrated metal ions polarize coordinated water molecules and, consequently, act as Brønsted-Lowry acids:
Their solutions, therefore, are acidic.
This process is known as hydrolysis.
Al(H2O)6 (aq) Al(OH)(H2O)5 (aq) + H+ (aq) 3+ 2+

40. Acidic and Basic Salts
Acidic Salts are formed from a strong acid and a weak base.
Neutral salts are formed from a strong acid and strong base.
Basic salts are formed from a strong base and a weak acid.
NaCl
NaC2H3O2
NH4Cl
HCl + NaOH
NaCl + H2O
s.a.
s.b.
neutral salt
HC2H3O2 + NaOH
NaC2H3O2 + H2O
basic salt
w.a.
s.b.
NH4OH
NH4Cl
+ H2O
HCl +
acidic salt
s.a.
w.b.

41. Acidic and Basic Salts Salts of Strong Acid-Strong Base Reactions:
NaCl, NaNO3, KBr, etc.; solutions are neutral
Salts of Weak Acid-Strong Base Reactions:
NaF, NaNO2, NaC2H3O2, etc.; solutions are basic
Salts of Strong Acid-Weak Base Reactions:
NH4Cl, NH4NO3, (CH3)2NH2Cl, C5H5NHCl;
Solutions of these salts are acidic
Salts of Weak Acid-Weak Base Reactions:
NH4C2H3O2, NH4CN, NH4NO2, etc..
These compounds can be acidic, basic, or neutral, which depends on the relative strength of the acid and the base.

42. Acidic and Basic Salts Basic Salt (with B) NaB(s)  Na+(aq) + B-(aq)
Kb =
[BH+][OH-]
[B-]
B-(aq) + H2O  BH+(aq) + OH-(aq)
Acidic Salt (with AH+)
AHCl(s)  AH+(aq) + Cl-(aq)
Ka =
[H+][A]
[HA+]
AH+(aq)  A (aq) + H+(aq)
What about AHB (with AH+ and B-)?
AHB(s)  AH+(aq) + B-(aq)
Generates H+
Generates OH-
Solutions in which both the cation and the anion hydrolyze:
Kb for the anion > Ka for the cation, solution will be basic
Kb for the anion < Ka for the cation, solution will be acidic
Kb for the anion  Ka for the cation, solution will be neutral

43. Predicting Acid-Base Property of Salts
Is NH4C2H3O2 acidic, basic or neutral?
NH4C2H3O2(s)  NH4+(aq) + C2H3O2-(aq)
NH4+(aq) + H2O  H3O+(aq) + NH3(aq) Ka = 5.6 x 10-10
C2H3O2-(aq) + H2O  HC2H3O2(aq) + OH-(aq) Kb = 5.6 x 10-10
Ka = Kb  NH4C2H3O2 is neutral

44. Predicting Acid-Base Property of Salts
Is (NH4)2SO4 acidic, basic or neutral?
(NH4)2SO4(aq)  2NH4+(aq) + SO42-(aq);
NH4+(aq) + H2O  H3O+(aq) + NH3(aq) Ka = 5.6 x 10-10
SO42-(aq) + H2O  HSO4-(aq) + OH-(aq) Kb = 8.3 x 10-13
Ka > Kb  (NH4)2SO4 is acidic.

45. Acidic and Basic Salts Summary
XY(s) X+(aq) + Y-(aq) Ka Kb

46. 15.14
Predict whether the following solutions will be acidic, basic, or nearly neutral:
NH4I
(b) NaNO2
(c) FeCl3
(d) NH4F
NH4I(s)  NH4+(aq) + I-(aq)
Acidic Salt
acid
very weak base
NaNO2(s)  Na+(aq) + NO2-(aq)
Basic Salt
neutral
base
FeCl3(s)  Fe+(aq) + 3Cl-(aq)
Acidic Salt
acid
very weak base
NH4F(s)  NH4+(aq) + F-(aq)
Acidic Salt
acid
base
Ka = 5.6 x 10-10
Kb = 1.4 x 10-11

47. Chapter 15

48. Oxides
Oxide is a chemical compound that contains at least one oxygen atom and one other element. Of the general from:
E can be any element other than O or H.
Oxides can be acidic, basic amphoteric.
ExOy

49. Most transition metal oxides are basic.
Oxides of highly electropositive metals are basic.
Most transition metal oxides are basic.
Oxides of electronegative nonmetals are acidic.

50. Oxides Oxides of electronegative nonmetals are acidic.
Acidity increases left to right
SiO2 < P4O10 < SO3 < Cl2O7
Acidity decreases top-to-bottom
N2O5 > P4O10 > As2O5 > Sb2O5
N2O5 + H2O  2HNO3
SO3 + H2O  H2SO4
Cl2O7 + H2O  2HClO4

51. Oxides Oxides of highly electropositive metals are basic.
Na2O(s) + H2O  2NaOH(aq)
MgO(aq) + HCl(aq)  MgCl2(aq) + H2O

52. Oxides
Some oxides are amphoteric: Can behave as an acid or a base depending on the circumstance.
Al2O3(s) + HCl(aq)  2AlCl3(aq) + H2O
Al2O3(s) + 2NaOH(aq) + 3H2O  2NaAl(OH)4(aq)

53. Chapter 15

54. Combine unpaired electrons
Lewis Acids and Bases
Lewis Dot Structure:
Needs 3 electrons
Need 1 electron each
Combine unpaired electrons
Gilbert Newton Lewis
( )
Also proposed a definition for acids and bases. Now known as Lewis acids.

55. No H+ or OH- created. No protons donated or accepted!
Lewis Acids and Bases
A base is any species that donates an electron pair.
An acid is any species that accepts an electron pair.
This definition greatly expands the classes of acids.
The acid-base reaction, in the Lewis sense, is the sharing of an electron pair between an acid and a base resulting in the formation of a bond:
A :B  A–B
F B F
N H • H
F B F
N H H +
acid
base
No H+ or OH- created. No protons donated or accepted!

56. 15.15
Identify the Lewis acid and Lewis base in each of the following reactions:
C2H5OC2H5 + AlCl (C2H5)2OAlCl3
(b) Hg2+(aq) + 4CN-(aq) (aq)
base
acid
acid
base
Here the Hg2+ ion accepts four pairs of electrons from the CN- ions.

57. Example
Identify the Lewis acid and Lewis base in each of the following reactions:
Cl– + AlCl3  AlCl4–
H2O + CO2  H2CO3
H+ + OH-  H2O
Cu NH3  Cu(NH3)42+
AlCl3 + Cl-  AlCl4-

58. Acid/Base Definitions
Arrhenius
acid is a substance that produces H+ in water
base is a substance that produces OH- in water
Brønsted
acid is a substance that donates H+
base is a substance that accepts H+
Lewis
acid is a substance that accepts a pair of electrons
base is a substance that donates a pair of electrons

59. Venn Diagram

60. Acid/Base Venn Diagram
All Brønsted-Lowry acids are Arrhenius acids.
Not all Arrhenius acids are Brønsted-Lowry acids.
etc…

61. Acid/Base Side Note Mg(OH)2 (s) + 2HCl (aq) MgCl2 (aq) + 2H2O (l)
NaHCO3 (aq) + HCl (aq)
NaCl (aq) + H2O (l) + CO2 (g)

62. Chapter 15