Unless otherwise stated, all images in this file have been reproduced from:
Blackman, Bottle, Schmid, Mocerino and Wille,
Chemistry, 2007 (John Wiley)
ISBN: 9 78047081 0866
e
CHEM1002 [Part 2]
A/Prof Adam Bridgeman (Series 1)
Dr Feike Dijkstra (Series 2)
Weeks 8 – 13
Office Hours:
Room:
e-mail:
e-mail:
Monday 2-3, Friday 1-2
543a
adam.bridgeman@sydney.edu.au
feike.dijkstra@sydney.edu.au
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Acids and Bases
Lecture 1:
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Common Acids and
Bases
Definitions
Equilibria
Conjugate acid-base pairs
Autoionisation of water
pH
Blackman Chapter 11, Sections 11.1-11.3
Reproduced from ‘The
Extraordinary Chemistry
of Ordinary Things, C.H.
Snyder, Wiley, 2002
(Page 245)
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Use of Common Acids and Bases
Substance
Formula
Use
Acids
Acetic acid
Citric acid
Phosphoric acid
Boric acid
Hydrochloric acid
CH3COOH
C6H8O7
H3PO4
B(OH)3
HCl
flavouring; preservative
flavouring
rust remover
mild antiseptic; insecticide
brick/ceramic tile cleaner
NaOH
NH3
Na2CO3
NaHCO3
oven cleaner
household cleaner
water softener; grease remover
fire extinguisher; baking powder
Bases
Sodium hydroxide
Ammonia
Sodium carbonate
Sodium hydrogen
carbonate
Reproduced from ‘The Extraordinary Chemistry of
Ordinary Things, C.H. Snyder, Wiley, 2002 (Page 231)
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Definitions
Arrhenius:


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H+(aq) + OH-(aq)
ACID: H+ producer in aqueous solution e.g. HCl
BASE: OH- producer e.g. NaOH
Brønsted - Lowry: H+ + A

H2O(l)
HA
ACID: proton donor (H+) e.g. HCl
BASE: proton acceptor e.g. NH3
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Acids, Bases & Equilibrium
HA(aq) + H2O(l)
H3O+(aq) + A-(aq)
• A STRONG acid has equilibrium to the right
(HA completely ionised)
• A WEAK acid has equilibrium to the left
(HA partly/mostly intact)
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Equilibrium Equation:
[H3O ][A  ] [H ][A  ]
Ka 

[HA]
[HA]
 Ka is the ACID DISSOCIATION CONSTANT
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Conjugate Acid-Base Pairs
• NH4+ is the conjugate acid of NH3
• NH3 is the conjugate base of NH4+
• A conjugate base has one less proton than its conjugate acid
• HSO4–:
conjugate base is SO42–
conjugate acid is H2SO4
• H2SO4 is a dibasic or diprotic acid:
H2SO4(aq) + H2O(l)
HSO4–(aq) + H2O(l)
H3O+(aq) + HSO4–(aq)
H3O+(aq) + SO42–(aq)
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Acid-Base Reactions
conjugate pair
ACID + BASE
BASE + ACID
conjugate pair
HF(aq)
+ H2O(l)
F-(aq)
+ H3O+(aq)
HCOOH(aq) + CN-(aq)
HCOO-(aq) + HCN(aq)
H2PO4-(aq)
+
HPO42-(aq) + H2O(l)
NH4+(aq)
+ CO32-(aq)
OH-(aq)
NH3(aq)
+ HCO3-(aq)
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Autoionisation of Water
2 H2O(l)
H3O+(aq) + OH–(aq)
• Equilibrium constant given special symbol:
Kw = [H3O+][OH– ]
NB: [H2O(l)] = constant
At 25 °C: Kw = 1.0  10-14
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Neutral solution:
Acidic solution:
Basic:
remember this
[H+] = [OH– ] = 1.0  10-7 M
[H+] > 1.0  10-7 M
[H+] < 1.0  10-7 M
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The pH Scale
Because the concentrations of acids and bases can vary over
many orders of magnitude, it is convenient to define a logarithmic
scale to compare them:
pH = log10[H+]
pOH = log10[OH-]
pH + pOH = 14
e.g. If [H+] = 1.0 x 10-6 M then pH = log(106) =  (6) = 6.00
Hence, pOH = 14.00 – 6.00 = 8.00 and [OH-] = 10-8.00
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The ‘p’ Convention
pH = – log10[H+]
pOH = – log10[OH– ]
pKw = – log10Kw = 14.00 at 25 °C
Acid :
pH < 7
Neutral: pH = 7
Basic: pH > 7
Since Kw = [H+][OH– ]:
log10 Kw = log10 [H+] + log10 [OH– ]
– log10 [H+] – log10 [OH– ] = – log10 Kw
pH + pOH = 14
pOH = 14 – pH
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Temperature Dependence of pH
H+ + OHH2O
Ea
ΔH0 = 56 kJ mol-1
• Kw = 1.0  10-14 only at 25 °C
• Reaction is endothermic: it is more
favourable at higher temperature
• For T > 25 °C, Kw > 10-14  pH + pOH  14 if T  25 °C
• For T < 25 °C, Kw < 10-14  neutral pH  7 if T  25 °C !
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[H+]
BASIC
pH
10-14
14
10-12
12
Household Ammonia
10-10
10
10-8
8
10-6
6
10-4
4
10-2
2
100
0
NEUTRAL
ACIDIC
1 M NaOH
}
Sea Water
Blood
Pure Water
Milk
Vinegar
Lemon Juice
Stomach Acid
1 M HCl
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Practice Examples
1.
Calculate the pH for solutions with each of the [H+(aq)] concentrations below
(a)
10.0 M
(b)
1.00 M
(c)
0.10 M
(d)
0.010 M
2.
Calculate the pH for solutions with each of the [OH-(aq)] concentrations below
(a)
10.0 M
(b)
1.00 M
(c)
0.10 M
(d)
0.010 M
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Summary: Acids & Bases 1
Learning Outcomes - you should now be able to:
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Complete the worksheet
List common acids and bases
Define acids & bases
Use pH and Kw
Answer Review Problems 11.1-11.11 and 11.128
in Blackman
Next lecture:
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Calculations involving acids and bases
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