NAME: ___________________________________
UNIT #11: Acids and Bases
pH and pOH
Neutralization Reactions
Oxidation and Reduction
1. SELF-IONIZATION OF WATER
a) Water molecules collide, causing a very small number to ionize in a reversible reaction:
H
2
O(l) + H
2
O(l) ↔ H
3
O
+
(aq) + OH
-
(aq)
water molecules hydronium ion hydroxide ion
b) The hydronium ion (H
3
O
+
) consists of a water molecule attached to a hydrogen ion
(H
+
) by a covalent bond; thus, H
3
O
+
and H
+
can be used interchangeably in a chemical
equation to represent a hydrogen ion in aqueous solution.
Simplified equation for self-ionization of water:
H
2
O(l) ↔ H
+
(aq) + OH
-
(aq)
c) Water is considered neutral since it produces equal numbers of H
+
and OH
-
ions.
Hydrogen ion concentration, shown as [H
+
], for water = 1.0 x 10
-7
M
Hydroxide ion concentration, shown as [OH
-
], for water = 1.0 x 10
-7
M
Self-ionization produces a tiny number of ions but explains how pure water can behave
as a very weak electrolyte.
d) Water is the usual solvent for acids and bases; the dissociation of acids or bases in an
aqueous solution increases either the [H
+
] or [OH
-
], resulting in an aqueous solution
that is no longer neutral.
2. DEFINITION OF ACIDS AND BASES
a) Arrhenius Model of Acids and Bases
1. Acid: A substance that contains hydrogen and ionizes to produce hydrogen ions in
aqueous solutions.
Ex. HCl(g) → H
+
(aq) + Cl
-
(aq)
2. Base: A substance that contains a hydroxide group and dissociates to produce
hydroxide ions in aqueous solution.
Ex. NaOH(s) → Na
+
(aq) + OH
-
(aq)
3. The Arrhenius model is limited because it does not describe all bases such as NH
3
(ammonia) and NaHCO
3
(baking soda/sodium bicarbonate). These substances
dissociate to form OH
-
in an aqueous solution but do not have the hydroxide
group in their formula and therefore, would not meet the definition of an
Arrhenius base.
NH
3
(aq) + H
2
O(l) ↔ NH
4+
+ OH
-
NaHCO
3
(s) + H
2
O(l) ↔ H
2
CO
3
(aq) + Na
+
(aq) + OH
-
(aq)
sodium bicarbonate carbonic acid
