Heat capacities and densities of electrolyte mixtures in aqueous solution — Application to the determination of apparent molar heat capacities and volumes for potassium triiodide and dioxoneptunium(V) perchlorate

Apparent molar heat capacities for KI 3(aq) were determined from flow-microcalorimetric measurements of KI(aq) solutions containing dissolved iodine. From these, the conventional partial molar heat capacity C ∞ p,2 ( I − 3, maq, 298.15 K) = 156±40 JK −1 mol −1 is estimated. Also, densities and heat capacities for NpO 2 ClO 4( aq) + HClO 4( aq) mixtures were measured. Preliminary values are reported for apparent molar heat capacities (at 298.15 K) and volumes (at 296.02 K) for NpO 2ClO 4(aq). From these, values for the ionic apparent molar volume and heat capacity of NpO + 2(aq) are calculated. Analysis of the data is done assuming deviations from Young's rule are small for the apparent molar heat capacities of simple electrolytes. This is shown to be true for aqueous solutions of NaCl( aq) + KBr( aq) (298.15 K and 348.15 K) and NaCl( aq) + MgCl 2( aq) (348.15 K).