For all practical purposes, the equivalent weight of a compound involved in a precipitation reaction can be found from Eq. [11.2] by letting Z equal the oxidation number of ion. The equivalent weight of BaCl2 is FW/2. The equivalent weight of Al2[SO4]3, considered either as an aluminum or as a sulfate salt, is FW/6. In certain cases, a salt may have more than one equivalent weight, depending on how it is used. Thus, the equivalent weight of K2HPO4 is FW/2 when potassium is the reacting ion, and FW/3 when the reacting ion is phosphate.