The Foundations of Chemistry

EXAMPLE 4-7 Displacement Reaction

Which of the following metals can displace hydrogen from water at room temperature? Write
balanced formula unit, total ionic, and net ionic equations for reactions that can occur.

Sn, Ca, Hg

Plan

The activity series, Table 4-12, tells us that tin and mercury cannotdisplace hydrogen from
water. Calcium is a very active metal (see Table 4-12) that displaces hydrogen from cold water
and forms calcium hydroxide, a strong base.

Solution

Ca(s)
2H 2 O(
)88nH 2 (g)
Ca(OH) 2 (aq)

Ca(s)
2H 2 O(
)88nH 2 (g)
[Ca^2 
(aq)
2OH(aq)]

Ca(s)
2H 2 O(
)88nH 2 (g)
Ca^2 
(aq)
2OH(aq)

You should now work Exercise 65.

3 Active Nonmetal
Less Active Nonmetal

[Salt of Less Active Nonmetal]88n[Salt of More Active Nonmetal]

Many nonmetalsdisplace less active nonmetals from combination with a metal or other
cation. For example, when chlorine is bubbled through a solution containing bromide ions
(derived from a soluble ionic salt such as sodium bromide, NaBr), chlorine displaces
bromide ions to form elemental bromine and chloride ions (as aqueous sodium chloride):

Cl 2 (g)
2[Na
(aq)
Br(aq)]88n2[Na
(aq)
Cl(aq)]
Br 2 (
)

chlorine sodium bromide sodium chloride bromine

The displacement reaction of

calcium with water at room

temperature produces bubbles of

hydrogen.

4-8 Displacement Reactions 151

Figure 4-4 Potassium, like other Group IA metals,

reacts vigorously with water. For this photograph,

the room was completely dark, and all of the light

you see here was produced by dropping a small

piece of potassium into a beaker of water.