Acid – Base Theory
Definitions:
Arrhenius:
An acid is a substance that increases the H+ (or H3O+)
concentration in an aqueous solution.
HCl + H 2O  H3O+ + ClHCl  H+ + Cl-
A base is a substance that increases the OH- concentration
in an aqueous solution.
NaOH(s)  Na+ + OH-
What about Na2CO3 ????
Bronsted-Lowry:
HCl(aq) + NaOH(aq) → HOH + NaCl
Acid = a proton donor in a RXN
Base = a proton acceptor in a RXN
Lewis:
An acid is an electron pair acceptor
H+
acid
A base is an electron pair donor
.. :O:H
..
..
H:O:H
..
water
Acid/Base reactions:
Produce water and a salt (and sometimes carbon dioxide).
Hint: concentrate on the water first. Remember, water has
the formula HOH.
Complete and balance the following:
HCl +
2 HCl +
KOH

Ca(OH)2
HOH + KCl

Require equal numbers
2HOH
+ CaCl2

1.
Ba(OH)2 + H3PO4
2.
HC2H3O2
+ NaOH
3.
H2SO4 +
KOH
4.
H2CO3 + NaOH
5.
Na2CO3 + HCl




6.
NH4OH +
H2SO4
7.
NH3 + HCl


Give a definition of an acid:
An acid is a proton donor (H+)
Give a definition of a base:
A base is a proton acceptor
Conjugate acids and Conjugate bases
HCl +
KOH
acid
Na2CO3 +
base
HOH + KCl
base
Na2CO3 +
base

conj. acid
2HCl

acid
2HCl
acid
H2CO3 + 2NaCl
conj. acid

conj. base
conj. base
H2O + CO2(g) + 2NaCl
conj. acid
conj. base
NH3 + HCl

NH4
+
+ Cl
What is a strong Acid?
An Acid that is 100% ionized in water.
Strong Acids:
100% ionized (completely dissociated) in water.
HCl + H2O

H3O+ + Cl-
often written as:
HCl

H+ + Cl-
Strong Acids:
100% ionized (completely dissociated) in water.
HCl + H2O

H3O+ + Cl-
Strong Acids:
Perchloric
HClO4
Chloric,
Hydrobromic,
Hydrochloric,
Hydroiodic,
Nitric,
Sulfuric,
HClO3
HBr
HCl
HI
HNO3
H2SO4
What is a strong Base?
A base that is completely dissociated in water (highly soluble).
NaOH(s)  Na+ + OHStrong Bases:
Group 1A metal hydroxides
(LiOH, NaOH, KOH,
RbOH, CsOH)
Heavy Group 2A metal hydroxides
[Ca(OH)2, Sr(OH)2, and
Ba(OH)2]
Weak Acids: “The Rest”
Strong Acids:
100% ionized (completely dissociated) in water.
HCl + H2O  H3O+ + ClNote the “one way arrow”.
Weak Acids:
Only a small % (dissociated) in water.
HC2H3O2 + H2O  H3O+ + C2H3O2Note the “2-way” arrow.
Why are they different?
Strong Acids:
HCl HCl
HCl
HCl
HCl
(H2O)
ADD WATER to MOLECULAR ACID
Strong Acids:
Cl-
(H2O)
H 3O +
H 3O +
H 3O +
Cl-
H3O+ ClH 3O +
ClCl-
Note: No HCl molecules remain in
solution, all have been ionized in water.
Weak Acid Ionization:
HC2H3O2
HC2H3O2
HC2H3O2
HC2H3O2
HC2H3O2
(H2O)

Add water to MOLECULES of WEAK Acid
Weak Acid Ionization:
HC2H3O2
HC2H3O2
HC2H3O2
HC2H3O2
HC
2HH
3OO
2
HC
2 3 2 (H O)
2

H30+
H30+
C2H3O2C2H3O2-
Note: At any given time only a small portion of the acid
molecules are ionized and since reactions are running in
BOTH directions the mixture composition stays the same.
This gives rise to an Equilbrium expression, Ka