Note 63 — Chapter IV · THE THEORY OF IONIZATION; IONIZATION AND ELECTRICAL CONDUCTIVITY

In the case of double salts, such as sodium-ammonium phosphate, and similar compounds, the dissociation leads to the formation of more than two products. The molecules of two or more different products may then be charged positively and, conversely, there may be two or more different products of dissociation carrying negative charges. We have, for instance, Na(NH4)HPO4 ⇄ Na+ + NH4+ + H+ + PO43− and Na(NH4)HPO4 ⇄ Na+ + NH4+ + HPO42−. In all cases the rule concerning the sum of all the charges, as expressed in (2), must be fulfilled, the charge on the phosphate ion, PO43−, being three times as great as that on a sodium, ammonium, or hydrogen ion; that on the acid phosphate ion, HPO42−, being twice as great.