1. Chapter 10
Acids and Bases

2. Review Chapter 6 Defined an Arrhenius acid and base
Defined a Bronsted-Lowry acid and base

3. The Brønsted-Lowry Concept of Acids and Bases
Brønsted-Lowry definitions
Acids are proton (H+) donors.

4. The Bronsted-Lowry Definition of Acid and Bases
A Brønsted–Lowry base is a proton (H+) acceptor.

5. The Brønsted-Lowry Definition of Acids and Bases
Putting the acid and base definitions together, an acid–base reaction is one in which a proton is transferred. The reaction need not occur in water.
Conjugate Acid-Base Pairs
Result from the transfer of a proton
The acid reactant loses the proton to produce a conjugate base product
The base reactant gains the proton to produce a conjugate acid product
Hence a conjugate acid-base pair are two chemicals (one reactant and one product) that differ by a hydrogen ion

6. Conjugate Pair Acid Base + Base Acid + Conjugate Pair Reaction 1 HF
H2O + F-
H3O+ +
Reaction 2
HCOOH
CN- +
HCOO-
HCN +
Reaction 3
NH4+
CO32- +
NH3
HCO3- +
Reaction 4
H2PO4-
OH- +
HPO42-
H2O +
Reaction 5
H2SO4
N2H5+ +
HSO4-
N2H62+ +
Reaction 6
HPO42-
SO32- +
PO43-
HSO3- +
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7. Acid and Base Strength
Also introduced in Chapter 6 and discussed Chapter 7 and 9 – Acid/Base strength
The strength of an acid/base, described by the equilibrium constant, describes the degree to which the compound dissociates into its ions
Strong acids and bases dissociate entirely in water – large equilibrium constants
Weak acids only partially ionize and therefore an equilibrium is established – small equilibrium constants

8. Acid and Base Strength
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Strong acid: HA(g or l) + H2O(l) H3O+(aq) + A-(aq)

9. Acid and Base Strength Weak acid: HA(aq) + H2O(l) H3O+(aq) + A-(aq)
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Weak acid: HA(aq) + H2O(l) H3O+(aq) + A-(aq)

10. Acid Dissociation Contants
Ka – indicates the degree to which an acid will ionize
Stronger acid – Ka >> 1 meaning complete dissociation
Weaker acid – Ka < 1
hence reactant favored

11. Acid and Base Strength Acids Bases Strong Strong
hydrochloric acid, HCl
sodium hydroxide, NaOH
hydrobromic acid, HBr
potassium hydroxide, KOH
hydroiodic acid, HI
calcium hydroxide, Ca(OH)2
nitric acid, HNO3
strontium hydroxide, Sr(OH)2
sulfuric acid, H2SO4
barium hydroxide, Ba(OH)2
lithium hydroxide, LiOH
perchloric acid, HClO4
Weak
Weak
Begin with H or contains a carboxylic acid group, -COOH
Amine group - NHx

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13. Acid and Base Strength
An acid base reaction always moves toward the weaker acid and the weaker base
Conjugate pairs
the weaker the acid, the stronger its conjugate base
the weaker the base, the stronger its conjugate base

14. Acid Dissociation Constants
Monoprotic acid – acids that have but one proton to give up – HCl, HF, HNO3, CH3COOH
Polyprotic acids – acids that can give up more than one proton – H2SO4, H3PO4, oxalic acid
Ionization occurs in a step wise manner

15. Acid Dissociation Constants
Polyprotic acids
acids with more than more ionizable proton
Ka1 =
[H3O+][H2PO4-]
[H3PO4]
H3PO4(aq) + H2O(l) H2PO4-(aq) + H3O+(aq)
= 7.2x10-3
Ka2 =
[H3O+][HPO42-]
[H2PO4-]
H2PO4-(aq) + H2O(l) HPO42-(aq) + H3O+(aq)
= 6.3x10-8
Ka3 =
[H3O+][PO43-]
[HPO42-]
HPO42-(aq) + H2O(l) PO43-(aq) + H3O+(aq)
= 4.2x10-13
Ka1 > Ka2 > Ka3

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ACID STRENGTH

17. Water as Both an Acid and a Base
Acid reaction with water
HA (aq) + H2O (l) → H3O+ (aq) + A- (aq)
H2O acts as a Brønsted-Lowry base
Base reaction with water
B: (aq) + H2O (l) → BH+ (aq) + OH- (aq)
H2O acts as a Brønsted-Lowry acid
Water is amphoteric
An amphoteric species is a substance that can react as an acid or a base

18. The Auto-ionization of Water
Highly purified water
auto-ionization of water
Conduct a small amount of electricity +
H2O(l)
H2O(l)
H3O+(aq)
OH-(aq)

19. H2O(l) + H2O(l) H3O+(aq) + OH-(aq)
Ion Product Constant for Water
Kw =
[H3O+][OH-]
= 1.0 x at 250C
A change in [H3O+] causes an inverse change in [OH-].
In an acidic solution, [H3O+] > [OH-]
In a basic solution, [H3O+] < [OH-]
In a neutral solution, [H3O+] = [OH-]

20. [H3O+] [OH-] [H3O+] > [OH-] [H3O+] = [OH-] [H3O+] < [OH-]
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Divide into Kw
[H3O+]
[OH-]
[H3O+] > [OH-]
[H3O+] = [OH-]
[H3O+] < [OH-]
ACIDIC SOLUTION
NEUTRAL SOLUTION
BASIC SOLUTION

21. Measuring Acidity in Aqueous Solution: pH
pH scale allows the expression of H3O+ concentration in less bulky numbers
pH is a number usually between 0 and 14 that indicates the hydronium concentration
Mathematically determined
pH = -log [H3O+]
10 -pH = [H3O+]

22. Laboratory Determination of Acidity
Measuring pH
pH meter
Indicator
Indicator paper strips

23. Buffer Solutions
Buffer: A combination of substances that act together to prevent a drastic change in pH; usually a weak acid and its conjugate base.
Rearranging the Ka equation shows that the value of [H3O+] depends on the ratio [HA]/[A-].
[H3O+] = Ka [HA]/[A-]
Most H3O+ added is removed by reaction with A- ,so [HA] increases and [A-] decreases. As long as these changes are small, the ratio [HA]/[A-] changes only slightly, and there is little change in the pH.

24. When 0. 010 mol of acid and 0. 010 mol of base are added to 1
When mol of acid and mol of base are added to 1.0 L of pure water and to 1.0 L of a 0.10 M acetic acid–0.10 M acetate ion buffer, the pH of the water varies between 12 and 2, while the pH of the buffer varies only between 4.85 and 4.68.

25. Optional Homework
Text – 10.32, 10.33, 10.34, 10.44, 10.46, 10.48, 10.50, 10.58, 10.60, 10.62, 10.64, 10.66, 10.68, 10.70, 10.72, 10.78, 10.80, 10.86, 10.94, , , ,
Chapter 10 Homework online