The Foundations of Chemistry

Solution

The more active halogen, Cl 2 , displaces the less active halogen, I 2 , from its compounds.

Cl 2 (g)
2NaI(aq)88nI 2 (s)
2NaCl(aq)

Cl 2 (g)
2[Na
(aq)
I(aq)]88nI 2 (s)
2[Na
(aq)
Cl(aq)]

Cl 2 (g)
2I(aq)88nI 2 (s)
2Cl(aq)

You should now work Exercise 64.

METATHESIS REACTIONS

In many reactions between two compounds in aqueous solution, the positive and

negative ions appear to “change partners” to form two new compounds, with no

change in oxidation numbers. Such reactions are called metathesis reactions.

We can represent such reactions by the following general equation, where A and B repre-
sent positive ions (cations) and X and Y represent negative ions (anions):

AX
BY88nAY
BX

For example, when we mix silver nitrate and sodium chloride solutions, solid silver chlo-
ride is formed and sodium nitrate remains dissolved in water:

AgNO 3 (aq)
NaCl(aq)88nAgCl(s)
NaNO 3 (aq)

Metathesis reactions result in the removal of ions from solution; this removal of ions
can be thought of as the driving forcefor the reaction—the reason it occurs. The removal
of ions can occur in three ways, which can be used to classify three types of metathesis
reactions:

1.Formation of predominantly nonionized molecules (weak or nonelectrolytes) in

solution; the most common such nonelectrolyte product is water

2.Formation of an insoluble solid, called a precipitate(which separates from the solu-

tion)

3.Formation of a gas (which is evolved from the solution)

1 Acid–Base (Neutralization) Reactions: Formation of a Nonelectrolyte

Acid–base reactions are among the most important kinds of chemical reactions. Many
acid–base reactions occur in nature in both plants and animals. Many acids and bases are
essential compounds in an industrialized society (see Table 4-13). For example, approxi-
mately 350 pounds of sulfuric acid, H 2 SO 4 , and approximately 135 pounds of ammonia,
NH 3 , is required to support the lifestyle of an average American for one year.
The reaction of an acid with a metal hydroxide base produces a salt and water. Such
reactions are called neutralization reactionsbecause the typical properties of acids and
bases are neutralized.

4-9

Pronounced “meh-tath-uh-sis.”

4-9 Metathesis Reactions 153

The manufacture of fertilizers

consumes more H 2 SO 4 andmore NH 3

than any other single use.