Aqueous salt solutions often are not neutral with respect to PH. Explain why?

Answer 1

It all has to do with equilibrium. Salt solutions often contain the conjugates of weak acids and bases, which act with water to produce an acid or base. For example, let's say you have the salt sodium acetate (a salt of acetic acid). A solution of this salt will be basic because it will "steal" a hydrogen from water:
CH3COO- + H2O => CH3COOH + OH-

Another example is the salt ammonium fluoride, (a salt of ammonia) which will react with water to procuce an acid:
NH4+ + H2O => NH3 + H3O+

Answer 2

Its a "tug of war"

A strong acid reacting with a strong base yields a neutral salt, e.g NaCl

A strong acid with a weak base yields an acidic salt, eg. NH4Cl

A weak acid with a strong base yields an alkaline salt, e.g. Na2CO3