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A metal will replace any metal ion in solution that it is above
Lithium in the activity series. If the metal is listed below the metal ion in
Potassium solution, no reaction occurs. For example, Ag(s) + CuCl 2 (aq) →
with water
Calcium
Combine directly with oxygen React with acids Never found free in nature Aluminum Increasing ability to hold electrons Increasing chemical activity sodium) react with water to yield metal hydroxides and hydro-
no reaction.
Sodium
React
The very active metals (lithium, potassium, calcium, and
Magnesium
Zinc
gen. For example,
Chromium
Iron
2 Na(s) + 2 H 2 O(l) → 2 NaOH(aq) + H 2 ↑
Nickel
Tin
Acids yield hydrogen ions in solution, and metals above
Lead
Often occur free in nature HYDROGEN hydrogen in the activity series will replace hydrogen to form a
metal salt. For example,
Copper
Mercury
Zn(s) + H 2 SO 4 (aq) → ZnSO 4 (aq) + H 2 ↑
Silver
Platinum
Gold
In general, the energy involved in replacement reactions is
less than the energy involved in combination or decomposition
reactions.
FIGURE 10.12 The activity series for common metals, together
with some generalizations about the chemical activities of the metals.
The series is used to predict which replacement reactions will take
place and which reactions will not occur. (Note that hydrogen is not a ION EXCHANGE REACTIONS
metal and is placed in the series for reference to acid reactions.) An ion exchange reaction is a reaction that takes place when
the ions of one compound interact with the ions of another
compound, forming (1) a solid that comes out of solution
(a precipitate), (2) a gas, or (3) water.
Replacement reactions take place as more active metals
A water solution of dissolved ionic compounds is a solution
give up electrons to elements lower on the list with a greater
of ions. For example, solid sodium chloride dissolves in water to
electron-holding ability. For example, aluminum is higher on
become ions in solution,
the activity series than copper. When aluminum foil is placed in
a solution of copper(II) chloride, aluminum is oxidized, losing + –
NaCl(s) → Na (aq) + Cl (aq)
electrons to the copper. The loss of electrons from metallic alu-
If a second ionic compound is dissolved with a solution of
minum forms aluminum ions in solution, and the copper comes
another, a mixture of ions results. The formation of a precipi-
out of solution as a solid metal (Figure 10.13).
tate, a gas, or water, however, removes ions from the solution,
2 Al(s) + 3 CuCl 2 (aq) → 2 AlCl 3 (aq) + 3 Cu(s) and this must occur before you can say that an ionic exchange
reaction has taken place. For example, water being treated for
domestic use sometimes carries suspended matter that is re-
moved by adding aluminum sulfate and calcium hydroxide to
the water. The reaction is
3 Ca(OH) 2 (aq) + Al 2 (SO 4 ) 3 (aq) → 3 CaSO 4 (aq) + 2 Al(OH) 3 ↓
The aluminum hydroxide is a jellylike solid, which traps the sus-
pended matter for sand filtration. The formation of the insolu-
ble aluminum hydroxide removed the aluminum and hydroxide
ions from the solution, so an ion exchange reaction took place.
In general, an ion exchange reaction has the form
AX + BY → AY + BX
where one of the products removes ions from the solution. The
calcium hydroxide and aluminum sulfate reaction took place
as the aluminum and calcium ions traded places. A solubil-
ity table such as the one in appendix B will tell you if an ionic
exchange reaction has taken place. Aluminum hydroxide is
insoluble, according to the table, so the reaction did take place.
FIGURE 10.13 This shows a reaction between metallic alumi-
No ionic exchange reaction occurred if the new products are
num and the blue solution of copper(II) chloride. Aluminum is above
copper in the activity series, and aluminum replaces the copper ions both soluble.
from the solution as copper is deposited as a metal. The aluminum Another way for an ion exchange reaction to occur is if a
loses electrons to the copper and forms aluminum ions in solution. gas or water molecule forms to remove ions from the solution.

262 CHAPTER 10 Chemical Reactions 10-12