3.1 Neutralization Reactions

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What happens when an acid such as \(\ce{HCl}\) is mixed with a base such as \(\ce{NaOH}\):

\(\ce{HCl(aq) + NaOH(aq) -> NaCl(aq) + H2O(l)}\)

When an acid and a base are combined, water and a salt are the products.

Salts are ionic compounds containing a positive ion other than H⁺ and a negative ion other than the hydroxide ion, OH^-.

Double displacement reactions of this type are called neutralization reactions.

We can write an expanded version of this equation, with aqueous substances written in their longer form:

H⁺_(aq) + Cl^-_(aq) + Na⁺_(aq) + OH^-_(aq) → Na⁺_(aq) + Cl^-_(aq) + H₂O_(l)

\(\ce{H^{+}(aq) + Cl^{-}(aq) + Na^{+}(aq) + {OH-(aq)} -> Na^{+}(aq) + Cl^{-}(aq) + H2O(l)}\)

Removing the spectator ions we get the net ionic equation:

\(\ce{H^{+}(aq) + {OH-(aq)} -> H2O(l)}\)

When a strong acid and a strong base are combined in the proper amounts - when [\(\ce{H+}\)] equals [\(\ce{OH-}\)] - a neutral solution results in which pH = 7. The acid and base have neutralized each other, and the acidic and basic properties are no longer present.

Salt solutions do not always have a pH of 7, however. Through a process known as hydrolysis, the ions produced when an acid and base combine may react with the water molecules to produce a solution that is slightly acidic or basic. We will not go into details here, but generally if a strong acid is mixed with a weak base there the resulting solution will be slightly acidic; if a strong base is mixed with a weak acid the solution will be slightly basic.