Reactions of Ions in
Solution
Objectives
Explains how to construct ionic equations
Discusses the reactions of HCl(g), H 2 SO 4 (l) and NH 3 (g) with water
Lists the reactions of acids and bases
Outlines how simple tests may be used to identify common anions and cations
In Chapter 4 we saw that ions are atoms (or groups of atoms bonded together) which
have lost or gained electrons. Loss of electrons produces positively charged ions
(cations), while the gain of electrons produces negatively charged ions (anions).
This chapter reviews some reactions of common ions. Such reactions are responsible
for most of the coloured products and bubbling gases often associated with the
chemistry laboratory.Dissolution of salts in water
Ions produced when salts dissolve
Water is a covalently bonded substance, and if we want substantial numbers of ions
in water we have to introduce them ourselves. The easiest way is to add a soluble salt
such as sodium chloride.
Dissolving sodium chloride destroys its crystal structure and frees the Naand
Clions which can then disperse through the body of the water. This process is
calledionic dissociation. The ions are loosely attracted to the surrounding water
molecules and are said to be hydrated. We represent this by ‘aq’, an abbreviation for
‘aqueous’ which means watery. In our example we write Na(aq) and Cl(aq). The
sum of the dissociation and hydration steps is called dissolution. The dissolution
may be summarized by the equation:
H 2 O
Na,Cl(s)Na(aq) + Cl(aq)The table of valencies for common ions on page 464 lists many of the ions met in the
college or school laboratory. (You are advised to learn this table.) We can use the
table to work out the ions produced when soluble salts are dissolved in water.6.1
Contents
6.1Dissolution of salts in
water 82
6.2Ionic equations 83
6.3Producing ions in water
by chemical reaction 86
6.4Acids and bases 90
6.5Reactions of acids 91
6.6Acids produced when
gases CO 2 , SO 2 and
NO 2 dissolve in water 95
6.7Reactions of the
hydroxide ion 95
6.8Use of reactions in the
identification of ions
in solution 97
6.8Revision questions 98
6
UNIT