From UCDavis Chemwiki

In our previous semester, we discussed a class of reactions called "neutralization reactions" which occur when we mix an acid solution with a base solution. Since the acid donates protons and the base accepts protons, we might expect, when mixing acid and base, to achieve a solution which is no longer acidic or basic. For example, if we mix together equal volumes of 0.1M HCl(aq) and 0.1M NaOH(aq), the following reaction occurs:

`HCl(aq)+NaOH(aq) -> Na+(aq)+Cl^(-) (aq)+H2O(l)`  (1)

The resultant solution is simply a salt solution with NaCl dissolved in water. This solution has neither acidic nor basic properties, and the pH is 7; hence the acid and base have neutralized each other. In this case, we have mixed together a strong acid with a strong base. Since both are strong and since we mixed equal molar quantities of each, the neutralization reaction is essentially complete.

We next consider mixing together a weak acid solution with a strong base solution, again with equal molar quantities of acid and base. As an example, we mix 100ml of 0.1M acetic acid (HA) solution (a weak acid) with 100ml of 0.1M sodium hydroxide (a strong base). In this discussion, we will abbreviate the acetic acid molecular formula CH3COOH as HA and the acetate ion CH3COO^- as A^-. The reaction of HA and NaOH is:

`HA(aq)+NaOH(aq) -> Na+(aq)+A^(-) (aq)+H2O(l)` (11)

A^- (aq) is the acetate ion in solution, formed when an acetic acid molecule donates the positive hydrogen ion. We have thus created a salt solution again, in this case of sodium acetate (NaA) in water.

Here we have discussed the neutralization reactions of a strong acid with a strong base, and a weak acid with a strong base. We can write similar neutralization reactions for (1) a strong acid reacting with a strong base to produce an insoluble salt and water, (2) a weak acid with a strong base to produce an insoluble salt and water, (3) a strong acid reactive with a weak base to produce a soluble salt, and (4) a weak acid reacting with a weak base to produce a soluble salt. Each of these reactions can be represented by its own unique net ionic equation.

Salts
So far our acid-base reactions have produced what we refer to as normal salts. Normal salts contain no ionizable H atoms or OH groups and produce neutral solutions when they completely ionize.  Some salts will ionize to form acidic or basic solutions. We classify these salts as acidic salts (a salt that contains an unreacted H⁺) or a basic salt (a salt that contains an unreacted OH^-) group. These acidic and basic salts, when in solution, can react to neutralize bases or acids respectively.