- SCH3U1 Acids and Bases
Sections 10.1
1
Learning Goals
1. What is Arrhenius's definition of an acid?
A base?
2. What is the Brønsted-Lowry definition of
an acid? A base?
3. What do the terms "strong" and "weak"
mean when applied to an acid or a base?
4. How are common acids and bases
named?
5. How is an acidic anhydride formed? A
basic anhydride?
2
Acids General Properties
• Acids are substances that exhibit the following
properties when dissolved in water:
– Acids taste sour. (Do NOT taste chemicals!)
– Acids produce a stinging sensation on the skin
when they enter an open wound.
– Acids turn the color of the indicator dye litmus
from blue to red.
– Acids react with many metals, such as magnesium,
zinc, and iron, to produce ionic compounds and
hydrogen gas.
– Acids react with bases, thereby losing their acidic
3
properties.
Table 10.1 Common Acids
4
Bases General Properties
• Bases exhibit the following properties when
dissolved in water:
– Bases taste bitter. (Do NOT taste chemicals!)
– Bases feel slippery or soapy on the skin.
– Bases turn the color of the indicator dye litmus
from red (pink) to blue.
– Bases react with acids, thereby losing their basic
properties.
5
Table 10.1 Common Bases
6
Conductivity of Strong Acids & Bases?
7
HCl = Strong Acid
8
Acetic Acid = Weak Acid
9
NaOH = Strong Base
10
Ammonia = Weak Base
11
Properties of Acids and Bases
•
•
•
•
•
•
Taste
Conductivity
Feel
Reaction with litmus paper
Reaction with active metals
Reaction with carbonate compounds
12
Properties of Acids and Bases
13
14
Arrhenius Theory
15
Arrhenius Theory
How would the following acids dissociate
in water according to Arrhenius?
What is the recognizable PATTERN?
HBr (aq) 
HClO4 (aq) 
LiOH (aq) 
Ba(OH)2 (aq) 
16
Arrhenius Theory
• In 1887 the Swedish chemist Svante
Arrhenius proposed:
– An acid is a substance that ionizes (breaks
up into ions) in water to produce 1 or more
H+ ions
– A base is a substance that dissociates in
water to form 1 or more OH- ions
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Let’s Use Arrhenius here…
• According to Arrhenius you have to have
and H+ and an OH- in the base of an acid or
base that is being dissociated to create an H+
or OH- in the products.
We know NH3
• This is not true!
is a base!
• NH3 (aq) + H2O (l)  NH4+ (aq) + OH- (aq)
Limitations to
Arrhenius Theory?
18
Limitations of Arrhenius Theory
• A free proton does not exist in water solutions.
Polarity of water?
O:
+ H+
H
Water
:
:
H
+
H
O
H
H
Hydrogen Ion
(proton)
Hydronium Ion
Hydronium Ion H3O+ – a hydrated proton,
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Brønsted-Lowry Theory
These shortcomings were overcome by
a theory proposed independently, in
1923, by J. N. Brønsted (Denmark) and
T. M. Lowry (London)
An acid is a proton donor
A substance that gives up H+ (a proton).
A base is a proton acceptor
A substance that accepts H+ (a proton).
TRANSFER OF A PROTON!!!
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Brønsted-Lowry Examples
Hydrogen Chloride in water is Hydrochloric acid
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Brønsted-Lowry Examples
Ammonia in water is a base
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Conjugate Acid-Base Pairs
By Brønsted-Lowry theory, the products of an
acid base reaction are also acids and bases.
CH3COOH
acid
+ H2 O
base
H3O+ + CH3COOconjugate conjugate
acid
base
An acid-base conjugate pair differs in structure only by a proton (H+):
CONJUGATE means “linked together”
• The conjugate acid of a species is that species plus a proton;
• The conjugate base of a species is that species minus a proton.
Brønsted-Lowry Notes
Like Arrhenius a Brønsted-Lowry acid must
have a H+.
*So all Arrhenius acids are also BrønstedLowry acids
However, any negative anion species can be a
Brønsted-Lowry base. (not only OH-)
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Conjugate Pairs Examples
Nitrous Acid
HNO2 (aq)
acid
+
H2O
base
H3O+
+
NO2-
conjugate conjugate
acid
base
Conjugate Acid Base Pairs
The conjugate base of HNO2 is NO2-,
the species that remains after HNO2 loses a proton.
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Conjugate Pairs Examples
Ammonia
NH3(aq)
base
+
H2O
acid
OH-
+
NH4+
conjugate conjugate
base
acid
Conjugate Acid Base Pairs
Notice acid-base pairs only differ by
one proton (H+)
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NH3(aq) + H3O+(l)
Arrhenius vs. Brønsted Lowry
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Strong Acids
• Acids that are completely ionized in water
solution are called strong acids.
H2O
HCl(g) ->
H+
(aq)
+
In 0.0010 mol/L HCl(aq)
[H+] = 0.0010 mol/L
[Cl-] = 0.0010 mol/L
[HCl] = 0 mol/L
Cl
(aq)
All the HCl is dissociated
in solution
29
Square Brackets indicates concentration
Weak Acids
• Acids that are only partially ionized in
aqueous solution are called weak acids.
H 2O
CH3COOH(aq)
H+ (aq) + CH3COO-(aq)
In 1.00 mol/L CH3COOH(aq)
only about 1% of the molecules ionize, most of it
remains as acetic acid molecules
In 1.000 mol/L CH3COOH (aq)
[H3O+] or [H+] = 0.010 mol/L
[CH3COO-] = 0.010 mol/L
[CH3COOH] = 0.99 mol/L
30
Monoprotic Acids
• One ionizable H atom per molecule
–
–
–
–
Hydrochloric Acid
Hydrofluoric Acid
Nitric Acid
Hydrocyanic Acid
HCl
HF
HNO3
HCN
31
Polyprotic Acids
• Diprotic Acids
Two ionizable H atoms per molecule
– Sulfuric Acid
H2SO4
– Carbonic Acid
H2CO3
• Triprotic Acids
Three ionizable H atoms per molucule
– Phosphoric Acid
H3PO4
32
Not all Hydrogens are Acidic
• None of the hydrogens in methane (CH4)
are given up in acidic solution
• Only one hydrogen in acetic acid (C2H4O2)
is acidic, that is why it is often written as
CH3COOH
33
How to tell the acidic hydrogens
1. We write a molecular formula with
ionizable H atoms first.
– HNO3 , H2SO4 , and H3PO4
Ionizable Hydrogens
– HC2H3O2,
Non-Ionizable Hydrogens
34
How to tell the acidic hydrogens
2. In organic chemistry, we often use formulas that
show the ionizable hydrogen atoms last.
Example carboxylic acids.
Ionizable Hydrogens
Acetic acid
Formic acid
Propionic acid
Butyric acid
CH3COOH
HCOOH
CH3CH2COOH
CH3CH2CH2COOH
Non-Ionizable Hydrogens
In each of these, only the H atom on the O atom is
ionizable.
35
Common Strong Acids
Hydrochloric acid
Hydrobromic acid
Hydriodic acid
Nitric acid
Sulfuric acid
Perchloric acid
HCl(aq)
HBr(aq)
HI(aq)
HNO3(aq)
H2SO4(aq)
HClO4(aq)
36
Common Bases
• Bases produce OH- ions in aqueous solution
(Arrhenius definition)
– Group 1 and 2 cations with hydroxide ions
• Examples:
NaOH Sodium Hydroxide (also known as lye)
KOH Potassium Hydroxide
Ca(OH)2 Calcium Hydroxide (a.k.a. slaked lime)
Strong Bases
Strong bases are completely ionize in water:
H2O
NaOH (s) 
Na+
(aq)
+
OH
(aq)
37
Strong Bases
Alkali metal hydroxides
Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Rubidium hydroxide
Cesium hydroxide
Alkaline earth hydroxides
Calcium hydroxide
Strontium hydroxide
Barium hydroxide
LiOH (aq)
NaOH (aq)
KOH (aq)
RbOH (aq)
CsOH (aq)
Ca(OH)2 (aq)
Sr(OH)2 (aq)
Ba(OH)2 (aq)
38
Weak Bases
Bases that are only partially ionized in
aqueous solution are called weak bases.
H2O
NH3 (g) + H2O
NH4+ (aq) + OH- (aq)
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Ammonia as a proton acceptor
• Lone pair can be used to accept proton
40