1. Acid-Base Equilibria: Acids and Bases
What makes an Acid an Acid?
An acid possess a sour taste
An acid dissolves active metals magnesium
An acid causes certain vegetable dyes to turn characteristic colors
What makes a Base a Base?
A bases possess a bitter taste
A base feels slippery to the touch
A base causes certain vegetable dues to turn a characteristic color

3. 7 strong acids and 8 strong bases
Acids - HI, HBr, HCl, HClO3, HClO4, H2SO4, HNO3
Bases – LiOH, NaOH, KOH, RbOH, CsOH, Ca(OH)2, Sr(OH)2, Ba(OH)2

4. The Arrhenius Definition of an Acid and a Base
An acid is a substance that produces H+ ions in water solutions
HCl  H+ + Cl-
A base is a substance that produces OH- ions in a water solution
NaOH  Na+ + OH-

5. acid dissociation equations
HC6H5O3  C6H5O31- + H+
Fe(H2O)63+  Fe(H2O)5(OH)2+ + H+
CH3CH2NH31+  CH3CH2NH2 + H+

6. When HCl dissolves in water we write: HCl(g)  H+(aq) + Cl-(aq)
The Proton in Water
When HCl dissolves in water we write:
HCl(g)  H+(aq) + Cl-(aq)

7. Reality for the Hydronium ion H5O2+

8. Acidic solutions are formed by a chemical reaction in which and acid transfers a proton (H+) to water, so we can write them either way.
HCl(aq) + H2O(aq)  H3O+(aq) + Cl-(aq) or
HCl(aq)   H+(aq) + Cl-(aq)

9. Nitrogen compounds are Bronsted acids when they are protonated.
NH4Cl
NH4+  NH3 + H+
CH3)2NH2+  (CH3)2NH + H+

10. The Bronsted-Lowry definition for Acids and Bases
Acids may be defined as a substance that is capable of donating protons
Bases may be defined as substance that accepts protons.
HCl + NH3  NH Cl-
acid base conjugate conjugate
acid base

11. Is Water an Acid?
NH3(aq) +H2O(aq)  NH4+(aq) + OH-(aq)

12. Is Water a Base?
HC2H3O2(aq) + H2O(aq)  H3O+(aq) +C2H3O21-(aq)

13. The auto ionization of water
The reaction occurs to a very small extent; about 1 in 108 molecules is ionized at any given moment H O : +  ..

14. Dissociation of Water, pH Scale
H2O(l)  H+(aq) + OH-(aq)
K =[H+] [OH-]
[H2O]
since water is a liquid and its concentration is therefore constant, this expression may be written as:
Kw = [H+] [OH-] = 1.0 x 10-14
[H+] = [OH-] = 1.0 x 10-7 M

15. Sample exercise: Indicate whether each of the following solutions is neutral, acidic, or basic:
[H+] = 2 x 10-5 M
[OH-] = M
[OH-] = 1.0 x 10-7 M

16. Calculate the concentration of H+(aq) in
a solution in which the [OH-] is 0.020M
a solution in which the
[OH-] = 2.5 x 10-6 M.
Indicate whether the solution is acidic or basic

18. If pH is 3.8 the H+ concentration is
The pH Scale
pH = -log [H+]
If [H+] = 2. 5 x 105 the pH is?
pH = -log [2. 5 x 10-5 ] = 4.6
If pH is 3.8 the H+ concentration is
Antilog -3.8= 1.58 x 10-4 M

19. In a sample of lemon juice, [H+] = 3.8 x 10-4 M. What is the pH?
A commonly available window cleaner has a [H+] = 5.3 x 10-9 M. What is the pH?
In a sample of freshly pressed apple juice has a pH of Calculate the [H+]

20. What if we took the –log of the Kw expression
Kw = [H+] [OH-] = 1.0 x 10-14
pKw = pH + pOH = 14

21. What is the pH, [H+], [OH-], of a solution with a pOH of 2.5?
Is the solution acidic or basic?

22. Major species HCl(aq) + H2O(aq)  H3O+(aq) + Cl-(aq) or
HCl(aq)   H+(aq) + Cl-(aq)
HC2H3O2(aq) + H2O(aq)  H3O+(aq) +C2H3O21-(aq)
Pb(NO3)2 + NaCl →NaNO3 + PbCl2

23. Indicators

25. What is the pH of 0.010 M solution of HCl?
If it ionizes completely which is what strong means then take the negative log of the concentration.
HCl(aq)  H+(aq) + Cl-(aq)
.01M M M
pH = 2

26. What is the pH of a solution made from 20mL of 2. 0M HCl and 35mL of 3
What is the pH of a solution made from 20mL of 2.0M HCl and 35mL of 3.2M HNO3?

27. H2SO4 → H+ + HSO41- (Strong) HSO41- → H+ + SO42- (Weak)
What about H2SO4
H2SO4 → H+ + HSO41- (Strong)
HSO41- → H+ + SO42- (Weak)

28. HX(aq)  H+(aq) + X-(aq), then
What about weak acids
HX(aq)  H+(aq) + X-(aq), then
Ka = [H+][X-]
[HX]
The smaller the value of the acid dissociation constant Ka, the weaker the acid

29. What is the Ka of a 0.10 M solution of formic acid (HCHO2) which has a pH = 2.38?
HCHO2  H CHO21- I C E
Ka = (.00417)2 = 1.8 x 10-4
.0958

30. What is the concentration of H+ ions in a 0
What is the concentration of H+ ions in a 0.10 M solution of HC2H3O2 (Ka = 1.8 x 10-5)? pH? % ionization?
HC2H3O2  H+ + C2H3O21- I
C X +X +X
E – X X X
1.8 x 10-5 = X X = 1.3 x 10-3
.10 – X pH = 2.87

31. percent dissociation
1.3 X x 100 = 1.3%
.10

32. What is the pH and percent ionization of a 0. 20 M solution of HCN
What is the pH and percent ionization of a 0.20 M solution of HCN? Ka = 4.9 x 10-10

33. Acid-Base Equilibria: Strong Bases
The most common soluble strong Bases are the hydroxides
of group IA and Ca, Ba and Sr
What is the pH of a M
solution of Ba(OH)2?

34. Anions of Weak Acids
Amines

35. Dealing with Weak Bases
The base dissociation constant Kb refers to the
equilibrium in which a base reacts with H2O to
form the conjugate acid and OH-
Weak base + H2O  conjugate acid + OH-
NH3 (aq) + H2O (l)  NH4 +(aq) + OH-(aq)
[NH4+] [OH-]
Kb =
[NH3]
Calculate the [OH-] in a 0.15 M solution of NH3.
NH H2O  NH OH- I C E

37. H2SO3(aq)  H+(aq) + HSO3-(aq) HSO3-(aq)  H+(aq) + SO32-(aq)
Polyprotic Acids
H2SO3(aq)  H+(aq) + HSO3-(aq)
Ka1 = 1.7 x 10-2
HSO3-(aq)  H+(aq) + SO32-(aq)
Ka2 = 6.4 x 10-8
Calculate the pH of a .1M solution

38. Anions of Weak Acids HC2H3O2(aq) + H2O(aq)  H3O+(aq) + C2H3O2- (aq)
Bronsted
acid
Bronsted
base
Conjugate
acid
Conjugate
base
A second class of weak base is composed of the anions of
weak acids Anions of weak acids can be incorporated into salts.
NaC2H3O2  Na+(aq) + C2H3O2- (aq)
C2H3O2- + H2O  HC2H3O2 + OH- Kb = 5.6 x 1010

39. NaOH(aq)+HC2H3O2(aq→H2O+NaC2H3O2
NaC2H3O2  Na+(aq) + C2H3O2-(aq)
Na+(aq) + H2O ← NaOH(aq) + H+(aq)
C2H3O2-(aq)+H2O HC2H3O2 (aq)+OH- (aq)

40. NH4Cl → NH4+ + Cl-
NH4+  NH3 + H+

41. NH4Cl
NaC2H3O2
NH4C2H3O2

42. Calculate the pH of a 0.01 M solution of sodium
Anions of Weak Acids
Calculate the pH of a 0.01 M solution of sodium
hypochlorite (NaClO)
ClO H2O  HClO OH- I C E

43. Now it’s you turn: the Kb for BrO- is 5.0 x 10-6.
Calculate the pH of a M solution of NaBrO

44. Ka and Kb NH4+(aq)  NH3(aq)+ H+(aq) Ka x Kb = Kw [NH4][OH- ]
NH3(aq)+ H2O NH4+ (aq)+ OH-(aq)
NH4+(aq)  NH3(aq)+ H+(aq)
[NH4][OH- ]
[H+][NH3]
Ka =
Kb =
[NH4+]
[NH3]
NH4+(aq)  NH3(aq) + H+ (aq)
NH3(aq) + H2O(l) NH4+(aq) + OH- (aq)
H2O  H+(aq) + OH-(aq)
When two reactions are added to give a third reaction, the
equilibrium constant for the third reaction reaction is given
by the product of the equilibrium constants for the two
added reactions
Ka x Kb = Kw
pKa + pKb = pKw

45. Calculate the (a) base-dissociation constant, Kb, for the
fluoride ion, is the pKa of HF = 3.17
pKa = -log Ka
3.17 = -log Ka
Antilog = 6.76 x 10-4
Since
Ka x Kb = Kw
(6.76 x 10-4)x Kb = 1.0 x 10-14
Kb = 1.0 x 10-14/ 6.76 x 10-4 = 1.5 x 10-11

46. Calculate the pKb for carbonic acid (Ka = 4.3 x 10-7)
Now it’s your turn

47. Acid-Base Properties of Salt Solutions
Anions of weak acids, HX, are basic and will react with
H2O to produce OH-
X- (aq) + H2O (l)  HX(aq) + OH-(aq)
Anions of strong acids, such as NO3-, exhibit no basicitiy,
these ions do not react with water and consequently do not
influence the pH
Anions of polyprotic acids, such as HCO3-, that still have ionizable protons are capable of acting as either proton donors or acceptors depending upon the magnitudes of the Ka or Kb

48. Predict whether the salt Na2HPO4 will form an acidic or
Anions of polyprotic acids, such as HCO3-, that still have ionizable protons are capable of acting as either proton donors or acceptors depending upon the magnitudes of the Ka or Kb
Predict whether the salt Na2HPO4 will form an acidic or
basic solution on dissolvingin water.
Na2HPO4  2Na+ (aq) + HPO4-
HPO4- acting like an acid
K3 = 4.2 x 10-13
HPO4-(aq) + H2O  H3O+ + PO43-(aq)
HPO4- acting like an base
1.0 x 10-14
HPO4- (aq) + H2O  H2PO42-(aq) + OH-(aq) Kw =
Kb =
6.2 x 10-8 Ka
So HPO- is the conjugate base of H2PO4-.
Since the K2 of H2PO4- = 6.2 x then:
1.6 x 10-7 =
Since Kb is larger than Ka, HPO4- will act like a base

49. Salt derived from a strong base and a strong acid will have a pH of 7
Salt derived from a strong base and a weak acid
will have a pH above 7
Salt derived from a weak acid and a weak base
depends upon whether the dissolved ion acts as
an acid or a base as determined by the size of
the Ka or Kb

50. Acid-Base Character and Chemical Structure
two things to consider polarity difference and
strength of the bond
HF > HCl > HBr > HI
(most polar least) Based on electronegativity
difference HF is the most polar but a weak acid
because the bond is so strong

52. Acid strength of oxyacids
The more oxygen's the stronger the acid because of the oxygen pulling the electrons towards themselves.
HClO4> HClO3> HClO2> HOCl