The Arrhenius Theory
of Acids and Bases
Arrhenius Theory of Acids and Bases:
an acid contains hydrogen and ionizes in
solutions to produce H+ ions:
HCl → H+(aq) + Cl-(aq)
Arrhenius Theory of Acids and Bases:
Neutralization
n 
a base contains an OH- group and ionizes
in solutions to produce OH- ions:
n 
NaOH → Na+(aq) + OH-(aq)
In Reality…
H+ + H2O → H3O+
Hydronium Ion
(Can be used
interchangeably with H+)
n 
Neutralization: the combination of H+
with OH- to form water.
H+(aq) + OH-(aq) → H2O (l)
Hydrogen ions (H+) in solution form
hydronium ions (H3O+)
Commentary on Arrhenius Theory…
One problem with the Arrhenius
theory is that it’s not comprehensive
enough. Some compounds act like acids
and bases that don’t fit the standard
definition.
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Bronsted-Lowry Theory
of Acids & Bases
for example…
Proton transfer
Bronsted-Lowry Theory of Acids & Bases:
n 
An acid is a proton (H+) donor
n 
A base is a proton (H+) acceptor
another
ACID
HCl(aq) + H2O(l) → H3O+(aq) + Cl-(aq)
Base
Water is a proton
donor, and thus an
example… acid.
CONJUGATE
BASE
NH3(aq) + H2O(l) → NH4+ (aq) + OH- (aq)
Acid
BASE
Ammonia is a proton
acceptor, and thus a
base
CONJUGATE
ACID
Water is a proton donor, and thus
an acid.
another example… CONJUGATE
ACID
BASE
NH3(aq) + H2O(l) → NH4+ (aq) + OH- (aq)
BASE
Ammonia is a proton
acceptor, and thus a
base
CONJUGATE
ACID
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Examples: In the following reactions, label
the conjugate acid-base pairs:
Conjugate acid-base pairs
n 
Conjugate acid-base pairs differ by
one proton (H+)
A conjugate acid is the particle formed
when a base gains a proton.
A conjugate base is the particle that
remains when an acid gives off a proton.
Amphoteric Substances
A substance that can act as both an
acid and a base (depending on what it is
reacting with) is termed amphoteric.
n 
n 
H3PO4 + NO2- çè HNO2 + H2PO4acid
base
c. acid
c. base
CN- + HCO3- çè HCN + CO32base
acid
c. acid c. base
n 
HCN + SO32- çè HSO3- + CNacid
base
c. acid c. base
n 
H2O + HF çè F- + H3O+
c. base c. acid
base acid
Properties of Acids and Bases
n 
ACIDS
n 
n 
n 
Water is a prime example.
n 
n 
Have a sour taste
Change the color of
many indicators
Are corrosive (react
with metals)
Neutralize bases
Conduct an electric
current
n 
BASES
n 
n 
n 
n 
n 
Have a bitter taste
Change the color of
many indicators
Have a slippery
feeling
Neutralize acids
Conduct an electric
current
Other Household Acids and Bases
n 
n 
n 
Antacid: a weak base that
neutralizes excess stomach
acid.
The pH of shampoo is
generally kept between 5
and 8.
Lemon juice is an acid
that is sometimes used to
help keep fruit looking
fresh.
What will happen to left apple?
Indicators“Way Cool” Cyber-lab:
http://www.miamisci.org/ph/
phlemon.html
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Strength of Acids and Bases
n 
A strong acid dissociates completely in sol’n:
n 
n 
A weak acid dissociates only partly in sol’n:
n 
n 
HNO2 ⇔ H+(aq) + NO2-(aq)
A strong base dissociates completely in sol’n:
n 
n 
The Lewis Theory
of Acids and Bases
HCl → H+(aq) + Cl-(aq)
NaOH → Na+(aq) + OH-(aq)
A weak base dissociates only partly in sol’n:
n 
NH3(aq) + H2O(l) ⇔ NH4+(aq) + OH-(aq)
Neutralization
The Lewis Theory of Acids & Bases
Lewis acid: a substance that can accept
an electron pair to form a covalent
bond (electron pair acceptor).
n 
n 
Lewis base: a substance that can
donate an electron pair to form a
covalent bond (electron pair donor).
n 
Example 1:
n 
n 
NH3 + H2O ↔ NH4+ + OH-
base
H
..
Example 2:
Ionization of NH3:
n 
H N H + H
acid
..
..O
H
Neutralization: the formation of a
coordinate covalent bond in which
both electrons originated on the
same (donor) atom.
H
n 
+
↔ H N H +
H
Auto-ionization of water:
..
O
..
H
-
..
O
..
H2O + H2O ↔ H3O+ + OH-
base
H
H + H
acid
..
..O
H
..
+
↔ H O H +
H
..
O
..
H
-
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Example 3:
n 
Acid Base Theories
Reaction of NH3 with HBr (a Lewis AND
a Bronsted-Lowry acid-base reaction):
n 
NH3 + HBr ↔ NH4+ + Br-
base
acid
H
..
H N H + H
..
Br
..
Lewis
H
+
↔ H N H +
H
..
..
-
Bronsted-Lowry
Br
Arrhenius
SUMMARY OF ACID-BASE THEORIES
Theory
Acid Definition
Acid-Base Reactions
Base Definition
Arrhenius
Theory
Any substance which
releases H+ ions in
water solution.
Any substance which
releases OH- ions in
water solution
BrǿnstedLowry Theory
Any substance which
donates a proton.
Any substance which
accepts a proton.
Lewis Theory
Any substance which
can accept an
electron pair.
Any substance which can
donate an electron pair.
n 
n 
Neutralization reactions: reactions
between acids and metal hydroxide
bases which produce a salt and water.
H+ ions and OH- ions combine to form
water molecules:
n 
Example 1: the reaction of HCl and NaOH
(there are 3 ways to write the chemical equation):
n 
Balanced formula unit equation:
n 
n 
n 
n 
n 
H+(aq) + OH-(aq) → H2O(l)
Balanced formula unit equation:
n 
n 
H+ + Cl- + Na+ + OH- → H2O + Na+ + Cl-
Net ionic equation:
n 
Example 2: Write the 3 types of equations for
the reaction of hydrobromic acid, HBr, with
potassium hydroxide, KOH.
HCl(aq) + NaOH(aq) → H2O(l) + NaCl(aq)
Total ionic equation:
H+(aq) + OH-(aq) → H2O(l)
Total ionic equation:
n 
n 
HBr(aq) + KOH(aq) → H2O(l) + KBr(aq)
H+ + Br- + K+ + OH- → H2O + K+ + Br-
Net ionic equation:
n 
H+(aq) + OH-(aq) → H2O(l)
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Example 3: Write the 3 types of equations for
the reaction of nitric acid, HNO3, with calcium
hydroxide, Ca(OH)2.
n 
Balanced formula unit equation:
n 
n 
Total ionic equation:
n 
n 
2HNO3(aq) + Ca(OH)2(aq) → 2H2O(l) + Ca(NO3)2(aq)
2H+(aq)+2NO3-(aq)+Ca2+(aq)+2OH-(aq)→2H2O(l)+Ca2++2NO3-(aq)
Net ionic equation:
n 
H+(aq) + OH-(aq) → H2O(l)
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