Strong acids and strong bases are those that ionize almost completely in a dilute aqueous solution. When a strong acid of a given concentration in a dilute aqueous solution ionizes, the resulting concentration of hydronium ions and the resulting concentration of the conjugate base are equal to the original concentration of the acid. Thus a 1M aqueous solution of hydroiodic acid exists as 1M (aq ) and 1M (aq ). Strong bases ionize in a similar manner. Since strong acids and bases ionize so completely, any ionization from the water itself may be neglected in cases of ordinary concentration of the acid or base. For concentrations less than M, the ionization of water must be included.
When acids contain more than one hydrogen atom (polyprotic acids), they are capable of donating more than one hydronium ion. Thus a strong polyprotic acid, such as sulfuric acid ( ), ionizes completely in water. However, the concentration of hydronium ions will be twice the concentration of the original sulfuric acid. When the pH of this solution is calculated, this higher concentration of hydronium ions must be used.
Weak acids and weak bases do not fully ionize in water. The acid ionization constant for a strong acid is easily calculated, since it can be assumed that the acid
