The Foundations of Chemistry

CaO is called quicklime. Ca(OH) 2 is

called slaked lime.

6-8 Oxygen and the Oxides 261

heat
(b) As 4 (s)O 2 (g) (excess)888n
heat
(c) Mg(s)O 2 (g)888n

Plan

(a) The reaction of a nonmetal oxide (acid anhydride) with water forms a ternary acid in which
the nonmetal (Cl) has the same oxidation state (7) as in the oxide. Thus, the acid is perchloric
acid, HClO 4.
(b) Arsenic, a Group VA nonmetal, exhibits common oxidation states of 5 and  5
2 3.
Reaction of arsenic with excessoxygen produces the higher-oxidation-state oxide, As 2 O 5. By
analogy with the oxide of phosphorus in the 5 oxidation state, P 4 O 10 , we might write the
formula as As 4 O 10 , but this oxide exists as As 2 O 5.
(c) The reaction of a Group IIA metal with oxygen produces the normal metal oxide—MgO
in this case.

Solution

(a) Cl 2 O 7 (
)H 2 O(
)88n2HClO 4 (aq)

heat

(b) As 4 (s)5O 2 (g)888n2As 2 O 5 (s)

heat

(c) 2Mg(s)O 2 (g)888n2MgO(s)

EXAMPLE 6-11 Predicting Reaction Products

Predict the products of the following pairs of reactants. Write a balanced equation for each
reaction.
(a) CaO(s)H 2 O(
)88n

(b) Li 2 O(s)SO 3 (
)88n

Plan

(a) The reaction of a metal oxide with water produces the metal hydroxide.
(b) The reaction of a metal oxide with a nonmetal oxide produces a salt containing the cation
of the metal oxide and the anion of the acid for which the nonmetal oxide is the anhydride.
SO 3 is the acid anhydride of sulfuric acid, H 2 SO 4.

Solution

(a) Calcium oxide reacts with water to form calcium hydroxide.

CaO(s)H 2 O(
)88nCa(OH) 2 (aq)

(b) Lithium oxide reacts with sulfur trioxide to form lithium sulfate.

Li 2 O(s)SO 3 (
)88nLi 2 SO 4 (s)

You should now work Exercises 70–73.

Combustion Reactions

Combustion,or burning, is an oxidation–reduction reaction in which oxygen combines
rapidly with oxidizable materials in highly exothermic reactions, usually with a visible
flame. The complete combustion of hydrocarbons,in fossil fuels for example, produces
carbon dioxide and water (steam) as the major products:

Hydrocarbons are compounds that

contain only hydrogen and carbon.