The Foundations of Chemistry

2 [Active Metal
Nonoxidizing Acid] 88n[Hydrogen
Salt of Acid]

A common method for the preparation of small amounts of hydrogen involves the reac-

tion of active metals with nonoxidizing acids, such as HCl and H 2 SO 4. For example, when

zinc is dissolved in H 2 SO 4 , the reaction produces zinc sulfate; hydrogen is displaced from

the acid, and it bubbles off as gaseous H 2. The formula unit equation for this reaction is

Zn(s)
H 2 SO 4 (aq)88nZnSO 4 (aq)
H 2 (g)

strong acid soluble salt

Both sulfuric acid (in very dilute solution) and zinc sulfate exist primarily as ions; so the

total ionic equation is

Zn(s)
[2H
(aq)
SO 42 (aq)]88n[Zn^2 
(aq)
SO 42 (aq)]
H 2 (g)

Elimination of spectator ions from the total ionic equation gives the net ionic equation:

Zn(s)
2H
(aq)88nZn^2 
(aq)
H 2 (g)

Table 4-12 lists the activity series.When any metal listed above hydrogen in this series

is added to a solution of a nonoxidizingacid such as hydrochloric acid, HCl, and sulfuric

acid, H 2 SO 4 , the metal dissolves to produce hydrogen, and a salt is formed. HNO 3 is the

common oxidizing acid.It reacts with active metals to produce oxides of nitrogen, but not

hydrogen, H 2.

EXAMPLE 4-6 Displacement Reaction

Which of the following metals can displace hydrogen from hydrochloric acid solution? Write

balanced formula unit, total ionic, and net ionic equations for reactions that can occur.

Al, Cu, Ag

Plan

The activity series of the metals, Table 4-12, tells us that copper and silver do notdisplace

hydrogen from solutions of nonoxidizing acids. Aluminum is an active metal that can displace

H 2 from HCl and form aluminum chloride.

Solution

2Al(s)
6HCl(aq)88n3H 2 (g)
2AlCl 3 (aq)

2Al(s)
6[H
(aq)
Cl(aq)]88n3H 2 (g)
2[Al^3 
(aq)
3Cl(aq)]

2Al(s)
6H
(aq)88n3H 2 (g)
2Al^3 
(aq)

You should now work Exercises 57 and 59.

Very active metals can even displace hydrogen from water. The reaction of potassium,

or another metal of Group IA, with water is also a displacement reaction:

2K(s)
2H 2 O(
)88n2[K
(aq)
OH(aq)]
H 2 (g)

Such reactions of very active metals of Group IA are dangerous, however, because they

generate enough heat to cause explosive ignition of the hydrogen (Figure 4-4).

H 2 SO 4 can function as an oxidizing
agent with other substances, but it is
not an oxidizing agent in its reaction
with active metals.

150 CHAPTER 4: Some Types of Chemical Reactions

Zinc reacts with dilute H 2 SO 4 to
produce H 2 and a solution that
contains ZnSO 4. This is a
displacement reaction.

Aluminum displaces H 2 from a
hydrochloric acid solution.