Thermodynamics of lonization of aqueous lodic acid, an “almost-strong” electrolyte

Abstract

We have made calorimetric measurements of enthalpies of dilution of aqueous iodic acid and have used these results for evaluation of the standard enthalpy of ionization of HIO₃(aq.). We have also made calorimetric measurements of enthalpies of addition of perchloric acid solution to aqueous solutions of KIO₃, KNO₃, NaIO₃, and NaNO₃ and have used these results to obtain further values for the standard enthalpy of ionization of HIO₃(aq.). On the basis of all these results, we have selected ΔH^o=−660±125 cal-mole⁻¹ as the best available standard enthalpy of ionization of HIO₃(aq.) at 298.15°K, compared to the previously accepted −2400 cal-mole⁻¹. Using the best available K=0.157 for ionization, we also obtain ΔG^o=1097 cal-mole⁻¹ and ΔS^o=−5.9 cal-^oK⁻¹-mole⁻¹ for ionization of HIO₃(aq) at 298.15°K.