NOTES: 19.1 – Acid-Base Theories
Acids & Bases have distinctive properties…
Properties of Acids and Bases:
ACIDS:
BASES:
Change the color of many indicators
Change the color of many indicators
Conduct an electric current
Conduct an electric current
The Arrhenius Theory of Acids & Bases:
● An acid is a compound that contains an H+, and
Example:
In Reality…
HCl + H2O  H3O+(aq) + Cl-(aq)
Hydronium Ion (can be used interchangeably with H +)
● A base is a compound that contains an OH- group and
.
Example:
Neutralization: the combination of
●
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.
Bronsted-Lowry Theory of Acids & Bases:
● An ACIDis a
● A BASE is a
for example…
HCl(aq) + H2O(l)  H3O+(aq) + Cl-(aq)
another example…
NH3(aq) + H2O(l)  NH4+(aq) + OH-(aq)
Conjugate acid-base pairs
● Conjugate acid-base pairs
**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.
Examples: In the following reactions, label the conjugate acid-base pairs:

a) H3PO4
+
NO2-
HNO2
+
H2PO4-
b) CN-
+
HCO3- 
HCN
+
CO32-
c) HCN
+
SO32-

HSO3-
+
CN-
d) H2O
+
HF

F-
+
H3O+
Amphoteric Substances
● A substance that can act as both an acid and a base (depending on what it is reacting with) is termed
AMPHOTERIC.
**
The Lewis Theory of Acids & Bases
● Lewis acid: a substance that can accept an electron pair to form a covalent bond (
).
● Lewis base: a substance that can donate an electron pair to form a covalent bond (
).
Example 1: ionization of NH3:
Example 2: auto-ionization of water:
Example 3: reaction of NH3 with HBr (is a Lewis AND a Bronsted-Lowry acid-base reaction):
SUMMARY OF ACID-BASE THEORIES:
Theory:
Acid definition:
Base definition:
Brǿnsted-Lowry Theory
Any substance which
______________________ in water
solution.
Any substance which
__________________________.
Any substance which
______________________ in water
solution.
Any substance which
__________________________.
Lewis Theory
Any substance which can
____________________________.
Any substance which can
____________________________.
Arrhenius Theory