The Arrhenius Theory of Acids and Bases Neutralization In Reality…

The Arrhenius Theory of Acids and Bases Neutralization In Reality…

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.
1
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
2
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
3
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
-
4
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)
5
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)
6