Upon completion of this module, you should be able to explain the differences between a strong acid and a weak acid and explain the differences between a strong base and a weak base. When an acid dissolves in water, a proton transfer from the acid to water to form a hydronium ion. This process is called dissociation. We can rank the strengths of a list of acids by the extent to which they ionize in aqueous solution. When a strong acid is added to water, 100 percent of the acid dissociates into ions. For example, a strong acid, hydrochloric acid is completely dissociated into hydronium and chloride ions in water.