Dissociation constant of nitric acid

The composition of nitric acid solutions is investigated by means Raman spectroscopy (RS). The results are compared to critically selected data from other authors. The value of the thermodynamic dissociation constant in an aqueous nitric acid solution at 25°C (K a = {H^ + } NO₃^ - '_ ²/ HN{O₃} '₇₍₎䃓 = 35. 5 ± 1. 5M) is determined by analyzing an extensive set of reliable and consistent literature and original data. Expressions for the dependences of the activity coefficient of undissociated HNO3 molecules ('₇₍{₎䃓}) and the mean ionic coefficient ('_ = {{ 'H} + { '₍₎䃓^ - }}) on the stoichiometric concentration of nitric acid in the range of 0–18 M are found.