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Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
181
Acids and Bases
Acids and Bases
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER
18
18.1 Acids and Bases: An Introduction
All aqueous solutions contain hydrogen ions (H ϩ ) and hydroxide ions
(OH Ϫ ). An acidic solution contains more H ϩ ions than OH Ϫ ions,
whereas a basic solution contains more OH Ϫ ions than H ϩ ions. A
neutral solution contains equal concentrations of H ϩ ions and OH Ϫ
ions. A hydronium ion (H 3 O ϩ ) is a hydrated hydrogen ion. The symbols H ϩ and H 3 O ϩ can be used interchangeably in chemical equations.
In the Arrhenius model of acids and bases, an acid is a substance that contains hydrogen and ionizes in aqueous solution to
produce hydrogen ions. A base is a substance that contains a hydroxide group and dissociates in aqueous solution to produce hydroxide
ions. In the more inclusive Brønsted-Lowry model, an acid is a
hydrogen-ion donor and a base is a hydrogen-ion acceptor. When a
Brønsted-Lowry acid donates a hydrogen ion, a conjugate base is
formed. When a Brønsted-Lowry base accepts a hydrogen ion, a
conjugate acid is formed. Two substances related to each other by
the donating and accepting of a single hydrogen ion are a conjugate
acid-base pair.
Example Problem 18-1
Identifying Conjugate Acid-Base Pairs
Identify the conjugate acid-base pairs in this reaction.
HClO 2 (aq) ϩ H 2 O(l) 3 H 3 O ϩ (aq) ϩ ClO 2
Ϫ (aq)
A hydrogen ion is donated by HClO 2 , which is the Brønsted-Lowry
acid in the forward reaction. The resulting conjugate base is ClO 2
Ϫ .
The base in the forward reaction is H 2 O, which accepts a hydrogen
ion to form the conjugate acid H 3 O ϩ .
Practice Problems
1. Identify the conjugate acid-base pairs in the following reactions.
a. H 2 SO 3 (aq) ϩ H 2 O(l) 3 HSO 3
Ϫ (aq) ϩ H 3 O ϩ (aq)
b. HPO 4
2Ϫ (aq) ϩ H 2 O(l) 3 H 2 PO 4
Ϫ (aq) ϩ OH Ϫ (aq)
c. HSeO 3
Ϫ (aq) ϩ H 2 O(l) 3 H 3 O ϩ (aq) ϩ SeO 3
2Ϫ (aq)