1. http://www.cdli.ca/courses/ http://www.cbhs.k12.nf.ca/adrianyoung/
Unit 2 Acids and Bases

2. Topics Properties / Operational Definitions Acid-Base Theories
pH & pOH calculations
Equilibria (Kw, Ka, Kb)
Indicators
Titrations
STSE: Acids Around Us

3. Operational Definitions
An Operational Definition is a list of properties, or operations that can be performed, to identify a substance.
See p. 550 for operational definitions of acids and bases

4. Operational Definitions (Properties – see p. 550)
Acids
pH < 7
taste sour
react with active metals (Mg, Zn) to produce hydrogen gas
Bases
pH > 7
taste bitter
no reaction with active metals
feel slippery
Sour – citric acid (lemons, limes, grapefruit), vinegar, sour candy
Bitter – unflavoured milk of magnesia, coffee, unsweetened chocolate

5. Operational Definitions
Acids
blue litmus turns red
react with carbonates to produce CO2 gas
Bases
red litmus turns blue
no reaction with carbonates

6. Operational Definitions
Acids
conduct electric current
neutralize bases to produce water and a “salt”
Bases
conduct electric current
neutralize acids to produce water and a “salt”
any ionic compound
any ionic compound

9. Acid-Base Theories 1. Arrhenius Theory (p. 549 )
acid – any substance that dissociates or IONIZES in water to produce H+ ions
ie. an acid must contain H+ ions

10. Arrhenius Theory eg. HCl(aq) → H+(aq) + Cl-(aq) H2SO4(aq) →
H+(aq) + HSO4-(aq)
H+(aq) + SO42-(aq)

11. Arrhenius Theory
base – any substance that dissociates in water to produce OH- ions
ie. a base must contain OH- ions

12. Arrhenius Theory eg. NaOH(aq) → Ca(OH)2(aq) → Na+(aq) + OH-(aq)
Ca+(aq) OH-(aq)

13. Arrhenius Theory Which is an Arrhenius acid?
a) KOH c) CH4
b) HCN d) CH3OH
Which is a Arrhenius base?

14. Limitations of Arrhenius theory (p.551)
H+ cannot exist as an ion in water.
The positive H+ ions are attracted to the polar water molecules forming HYDRONIUM ions or H3O+(aq)
H+(aq) + H2O(l) → H3O+(aq)

15. Limitations of Arrhenius theory
CO2 dissolves in water to produce an acid.
NH3 dissolves in water to produce a base.
Neither of these observations can be explained by Arrhenius theory

16. Limitations of Arrhenius theory
Some acid-base reactions can occur in solvents other than water.
Arrhenius theory can explain only aqueous acids or bases.

17. Limitations of Arrhenius theory
Arrhenius theory is not able to predict whether certain species are acids or bases.
eg. NaHSO4 H2PO4- HCO3-
Arrhenius theory needs some work

18. To be used when Arrhenius is inadequate
Acid-Base Theories
To be used when Arrhenius is inadequate
2. Modified Arrhenius Theory (p. 552)
acid – any substance that reacts with water to produce H3O+ ions
eg.
HCl(g) + H2O(l) → H3O+(aq) + Cl-(aq)

19. Modified Arrhenius Theory
base – any substance that reacts with water to produce OH- ions
eg.
NH3(aq) + H2O(l) )→ NH4+(aq) + OH-(aq)
pp. 558, 559 #’s 1, 3, 8, & 9

22. 3. Brønsted-Lowry Theory (p. 553)
Acid-Base Theories
3. Brønsted-Lowry Theory (p. 553)
acid – any substance from which a proton (H+) may be removed
ie. an acid is a substance that loses a proton (H+)

23. Brønsted-Lowry Theory
base – any substance that can remove a proton (H+) from an acid.
ie. a base is a substance that gains a proton (H+)
In BLT , an acid-base reaction
requires the transfer of a proton
(H+) from an acid to a base.

24. Brønsted-Lowry Theory
conjugate acid
base
eg.
HCN(aq) + NH3(aq) → ←
CN-(aq) + NH4+(aq)
conjugate base
acid

25. Brønsted-Lowry Theory
What is a conjugate acid-base pair?? (p. 554)
Two particles (molecules or ions) that differ by one proton are called a conjugate acid-base pair.
The conjugate base forms when an acid loses a proton.
The conjugate acid forms when a base gains a proton (H+).

26. Brønsted-Lowry Theory
conjugate acid
base
conjugate base
acid

27. Brønsted-Lowry Theory
conjugate acid
base
eg.
NH3(aq) + H2O(l) → NH4+(aq) + OH-(aq)
H2O(l) H2O(l) → ←
conjugate base
acid ←

28. Brønsted-Lowry Theory
- an amphoteric substance can be either an acid or a base
these include WATER and negative ions that contain at least one hydrogen atom
eg. H2O, HCO3-(aq), H2PO4-(aq)

29. Brønsted-Lowry Theory
p.557 #’s 1 – 7
p #’s 8, 9
p #’s 2, 4-7, 10,11
Quiz - Tuesday Mar. 1

30. Strength of Acids and Bases
Strong acids produce more H+ ions
OR more H3O+ ions than weak acids
with the same molar concentration
A strong acid is an acid that ionizes or dissociates 100% in water
eg. HCl(aq)→
Strong acids react 100% with water (BLT)
eg. HCl(aq) + H2O(l) →
H+(aq) + Cl-(aq)
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball
H3O+(aq) + Cl-(aq)

31. Strength of Acids and Bases
NOTE: The equilibrium symbol, º , is NOT used for strong acids because there is NO REVERSE REACTION.
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

32. Strength of Acids and Bases
A weak acid is an acid that ionizes or dissociates LESS THAN 100%
eg. HF(aq)
Weak acids react less than 100% with water
eg. HF(aq) + H2O(l)
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

33. Strength of Acids and Bases
For weak acids, an equilibrium is established between the original acid molecule and the ions formed.
DO NOT confuse the terms strong and weak with concentrated and dilute.
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

34. Strength of Acids and Bases
eg. Classify the following acids:
mol/L HCl(aq)
strong and dilute
12.4 mol/L HCl(aq)
strong and concentrated
10.5 mol/L CH3COOH(aq)
weak and concentrated
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

35. Strength of Acids and Bases
monoprotic – acids that contain or lose one proton
diprotic – acids that contain or lose two protons
polyprotic – acids that have more than one proton
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

36. Strength of Acids and Bases
A strong base is a base that dissociates 100% in water, or reacts 100% with water, to produce OH- ion.
The only strong bases are hydroxide compounds of most Group 1 and Group 2 elements
eg. NaOH(s) →
Ca(OH)2(s) →
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

37. Strength of Acids and Bases
A weak base is a base that reacts less than 100% in water to produce OH- ion.
eg. S2-(aq) + H2O(l) º HS-(aq) + OH-(aq)
Football analogy:
- SA like the QBack that delivers the ball;
- WA like the QB that holds onto it
- SB is like the wide receiver that always catches the ball:100% completion
- WB is like the wide receiver that tends to drop the ball

38. Writing Acid-Base Equations (BLT)
Step 1: List all the molecules/ions present in the solution
ionic compounds form cations and anions
strong acids exist as hydronium ion and the anion (conjugate base)
for weak acids use full formula of the compound (i.e. un-ionized molecule)
always include water in the list.

39. Writing Acid-Base Equations (BLT)
Step 2: Identify the strongEST acid and the strongEST base from Step 1.
Step 3: Write the equation for the reaction by transferring a proton from the strongest acid to the strongest base.

40. Writing Acid-Base Equations (BLT)
Step 4: Determine the type of reaction arrow to use in the equation.
Stoichiometric (100%) reactions occur between:
Hydronium (H3O+) and bases stronger than nitrite (NO2-)
hydroxide (OH-)and acids stronger than hypochlorous acid (HOCl)

41. Writing Acid-Base Equations (BLT)
Step 5: Determine the position of the equilibrium by comparing the strengths of both acids in the equation.
The favoured side is the side with the weaker acid! 

42. Writing Acid-Base Equations (BLT)
Sample problems:
Write the net ionic equation for the acid-base reaction between:
- aqueous sodium hydroxide (NaOH(aq)) and hydrochloric acid (HCl(aq)).

43. H3O+(aq) + OH-(aq) → 2 H2O(l)
species present
Na+(aq)
OH-(aq)
H3O+(aq)
Cl-(aq)
H2O(l)
strongest acid
strongest base
H3O+(aq) + OH-(aq)
H2O(l) + H2O(l) OR
H3O+(aq) + OH-(aq) → 2 H2O(l)

44. Writing Acid-Base Equations (BLT)
Sample problems:
Write an equation for the acid-base reaction between nitrous acid (HNO2(aq)) and aqueous sodium sulfite (Na2SO3(aq)).

45. º HNO2(aq) Na+(aq) SO32-(aq) H2O(l) HNO2(aq) + SO32-(aq)
species present
HNO2(aq)
Na+(aq)
SO32-(aq)
H2O(l) SB SA
HNO2(aq) + SO32-(aq)
NO2-(aq) + HSO3 - (aq)
Weaker Acid
Stronger Acid
Products favored

46. Write the Net Ionic Equation for each aqueous reaction below:
Na2CO3(aq) and CH3COOH(aq)
NH3(aq) and HNO2(aq)
HNO3(aq) and RbOH
H2SO4(aq) and K3PO4(aq)
HF(aq) and NH4CH3COO(aq)
CaCl2(aq) and PbSO4(aq)
p #’s 10 &11
Acids & Bases #3

47. º H2O(l) Na+(aq) CH3COOH(aq) CO32-(aq) species present SB SA
CH3COO-(aq) + HCO3-(aq)
Stronger Acid
Weaker Acid
Products Favoured

48. º NH3(aq) HNO2(aq) H2O(l) HNO2(aq) + NH3(aq) NO2-(aq) + NH4 + (aq)
species present
NH3(aq)
HNO2(aq)
H2O(l) SA SB
HNO2(aq) + NH3(aq)
NO2-(aq) + NH4 + (aq)
Weaker Acid
Products favored
Stronger Acid

49. H3O+(aq) + OH-(aq) → 2 H2O(l)
species present
NO3-(aq)
Rb+(aq)
H3O+(aq)
OH-(aq)
H2O(l)
strongest acid
strongest base
H3O+(aq) + OH-(aq)
H2O(l) + H2O(l) OR
H3O+(aq) + OH-(aq) → 2 H2O(l)

50. species present
HSO4-(aq)
K+(aq)
PO43-(aq)
H3O+(aq)
H2O(l) SA SB
H3O+(aq) + PO43-(aq)
H2O(l) + HPO42-(aq)

51. º HF(aq) H2O(l) species present NH4+(aq) CH3COO-(aq) SA SB Weaker Acid
HF(aq) + CH3COO-(aq)
F-(aq) + CH3COOH(aq)
Weaker Acid
Products favored
Stronger Acid

52. º Ca2+(aq) Cl-(aq) Pb2+(aq) SO42-(aq) H2O(l) strongest acid
species present
Ca2+(aq)
Cl-(aq)
Pb2+(aq)
SO42-(aq)
H2O(l)
strongest base
H2O(l) + SO42-(aq)
HSO4-(aq) + OH-(l)
Weaker Acid
Reactants favored
Stronger Acid

53. NO!! Products are NOT always favoured
Try these:
CH3COOH(aq) + NH4F(aq)
HCN(aq) + NaHS(aq)

54. Acid-Base CalculationsKw
Ka Kb
[H3O+] [OH-]
pH pOH

55. Kw (Ionization Constant for water)
With very sensitive conductivity testers, pure water shows slight electrical conductivity.
PURE WATER MUST HAVE
A SMALL CONCENTRATION OF
DISSOLVED IONS

56. Kw Kw = K = Auto-Ionization of water H2O(l) + H2O(l)
º H3O+(aq) + OH-(aq)
Kw =
K =
[H3O+] [OH-]
[H2O] [H2O]

57. Kw In pure water at 25 °C; [H3O+] = 1.00 x 10-7 mol/L
[OH-] = 1.00 x 10-7 mol/L
Calculate Kw at 25 °C.

58. GET REAL!! H2O(l) + H2O(l) º H3O+(aq) + OH-
LCP: What happens if we add OH- ions (NaOH(aq)) to water?
shift to the left
[H3O+] ?
[OH-] ?
Does Kw change?
GET REAL!!

59. Kw = [H3O+] [OH-] [H3O+] [OH-] 1.00 x 10-14 = [H3O+] [OH-] 0.00357 M
4.89 x 10-3 mol/L
12.5 M
1.50 mol/L
2.80 x 10-12
2.04 x 10-12
8.00 x 10-16
6.67 x 10-15

60. Calculations with Kw (p. 564 – 566)
For strong acids and strong bases, the [H3O+] and [OH-] may be calculated using the solute concentration.
eg. What is the [H3O+] in a 2.00 mol/L solution of HNO3(aq)?
Ans: mol/L
[OH-] = ???

61. Calculations with Kw Ans: 4.00 mol/L
eg. What is the [OH-] in a 2.00 mol/L solution of NaOH(aq)?
Ans: mol/L
eg. What is the [OH-] in a 2.00 mol/L solution of Ca(OH)2(aq)?
Ans: mol/L
[H3O+] = ???

62. Calculations with Kw Ans: 0.150 mol/L
eg. What molar concentration of Al(OH)3(aq) is needed to obtain a [OH-] = mol/L?
Ans: mol/L

63. What is the [H3O+] and [OH-] in:
[H3O+] mol/L
[OH-]
mol/L
1.0 x 10-8
1.0 x 10-6
5.00 x 10-14
0.200
1.50
6.67 x 10-15
1.0 x 10-2
1.0 x 10-12

64. p. 566 #’s 12 - 15 solute [H3O+] [OH-] 0.680 mol/L HCl(aq) 1.50 M NaOH
M Ca(OH)2(aq)
_____ mol/L HClO4(aq)
0.450 M
____ mol/L Mg(OH)2(aq)
0.500 mol/L
0.680
1.47 x 10-14
6.67 x 10-15
1.50
1.00 x 10-13
0.100
0.450
2.22 x 10-14
0.250
2.00 x 10-14
p #’s

65. By what factor does the [H3O+] change when the pH value changes by 1?
pH and pOH (See p. 568)

66. The [H3O+] changes by a factor of 10 (10X) for each pH changes of 1.
pH and pOH (See p. 568)

67. pH and pOH FORMULAS pH = -log [H3O+] pOH = -log [OH-] [H3O+] = 10-pH
[OH-] = 10-pOH

68. pH and pOH eg. What is the pH of a 0.0250 mol/L solution of HCl(aq)?
What is the pOH of a mol/L solution of NaOH(aq)?
What is the pH of a 1.25 mol/L solution of KOH(aq)?
[H3O+] = mol/L
pH = 1.602
[OH-] = mol/L
pOH = 3.06
[OH-] = 1.25 mol/L
[H3O+] = 8.00 x mol/L
pH =

69. Significant digits in pH values?
The number of significant digits in a concentration should be the same as the number of digits to the right of the decimal point in the pH value.
eg. In a sample of OJ the
[H3O+] = 2.5 × 10−4 mol/L
pH = (See p. 568)

70. [H3O+]
[OH-] pH
pOH
0.0035
1.2 x 10-5
4.68
9.15
8.33 x 10-15
-1.10

71. [H3O+]
[OH-] pH
pOH
0.0035
1.2 x 10-5
4.68
9.15
8.33 x 10-15
-1.10
2.9 x 10-12
2.46
11.54
8.3 x 10-10
9.08
4.92
2.1 x 10-5
4.8 x 10-10
9.32
1.4 x 10-5
7.1 x 10-10
4.85
14.079
1.20
-0.079
7.9 x 10-16 13
15.10

72. pH, pOH and Kw p. 569 #’s 16 – 19 p. 572 #’s 20 – 25
Examine #23. Where is the energy term in this equation?
H2O(l) + H2O(l) º H3O+(aq) + OH-(aq)

73. Dilutions
When a solution is diluted the number of moles does not change.
OR ninitial = nfinal
CiVi = CfVf

74. eg. 400. 0 mL of water was added to 25
eg mL of water was added to 25.0 mL of HCl(aq) that had a pH of Calculate the pH of the resulting solution.
calculate [H3O+]
dilution formula
calculate pH

75. Before dilution: [H3O+] = 10-3.563 = 2.753 x 10-4 After dilution:
(2.753 x 10-4) (25.0 mL) = (Cf)(425.0 mL)
[H3O+] = x 10-5
pH = -log (1.609 x 10-5)
= 4.793
p #’s