3.1 Neutralization Reactions
What happens when an acid such as HCl is mixed with a base such as NaOH:
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)
Removing the spectator ions we get the net ionic equation:
H+(aq) + OH-(aq) → H2O(l)
When a strong acid and a strong base are combined in the proper amounts - when [H+] equals [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.