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Reactions of Acids


A. Reaction with a Base
Neutralization is the reaction of an acid with a base to form water and a salt (Section 8.2D1), as in the reaction of hydrochloric acid with sodium hydroxide:

The net ionic equation (Section 11.6) is

H+ + OH- H2O

We have seen acid-base reaction within the Brønsted-Lowry system as the reaction of a proton donor with a proton acceptor, as in the reaction of hydrochloric acid with the acetate ion:

or with ammonia:


B. Reactions with a Metal
Acids react with some metals in displacement reactions (Section 8.2C) to form hydrogen gas and a salt, as in the reaction of zinc with sulfuric acid:

Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)

Writing this reaction as a net ionic equation emphasizes that it is an oxidation-reduction reaction:

2 H+ + Zn Zn2+ + H2

in which zinc is oxidized and hydrogen reduced.


Example:

Write net ionic equations showing the reaction of hydrochloric acid with

a. Sodium nitrite

b. ammonia

c. magnesium

Solution

The net ionic equation will sow only the reaction of the proton of hydrochlric acid with the base provided by the reactants in parts a and b or with the metal magnsium in part c.

a. The base is the nitrite ion:

H+ + NO2- HNO2    nitrous acid

b. The base is ammonia:

H+ + NH3 NH4+    ammonium ion

c. The reactant is magnesium metal:

2 H+(aq) + Mg(s) Mg2+(aq) + H2(g)

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