The apparent hydration of ions. Part IV. The densities and viscosities of saturated solutions of silver nitrate in nitric acid

Determinations have been made at 25° of the solubility of silver nitrate in aqueous nitric acid of concentrations up to 12N. The densities and the viscosities of the solutions have been measured together with those of a comparable series for the acid alone. The formula d = K + k₁a + k₂b applies to the densities of the mixed solutions of total solute concentration below 9N, a and b being the concentrations of acid and salt respectively. The constants K and k₁ also apply to the pure acid solutions of concentrations 6 - 9N. The corresponding solution volumes are discussed and compared with those derived by other investigators. The silver ion behaves like lithium and sodium ions in having an apparent volume less than that calculated from its radius in the crystal lattice. The viscosity data are interpreted by means of the empirical formula ?₂ - ?₁ = 1/2(?₂ + ?¹)2.5f. A change of viscosity caused by the addition to a solution of ions of volume f is proportional to this volume but also depends upon the mean viscosity of the solutions considered. It is suggested that this latter factor takes account of the electrical effects, and hence the equation allows of the volume effect being separately estimated. The formula, which has previously been applied only to chlorides and their ions, is now found to give a satisfactory account of the data for nitric acid and for its mixed solutions with silver nitrate. The volume effect of the nitrate ion remains substantially constant except in 0 - 5N-solutions of the acid alone, where apparent variations due to the depolymerising action of the ion are indicated. This depolymerisation of the water is more easily effected by the nitrate ion than by the chlorine ion. The volume of the nitrate ion determined from the viscosities approximates to the solution volume calculated from the densities and is also in agreement with values deduced from the data for the size of this ion in crystals; hence it is concluded that this ion is not hydrated. Nitric acid shows a less complex behaviour in solutions of high concentration than does hydrochloric acid, and this suggests the absence of complex ions in the former case. The silver ions in the mixed solutions show effects attributable to hydration, which is less than that previously found for sodium but greater than for potassium, and this is in accordance with the expected results deduced from the sizes of the ions. Hydration factors for silver ions varying from 1.4 - 0.90 are found, whereas those for sodium ions were 1.7 - 1.2.