Solubility of Nitrous Acid (HONO) in Sulfuric Acid Solutions

Abstract

The Henry's law solubility of nitrous acid (HONO) has been studied in sulfuric acid solutions as a function of acid concentration in the range 0.3−73.6 wt % and temperature between 248 and 298 K by measuring the distribution of HONO between the gas and liquid phases using a bubbler-type gas−liquid reactor. Gas phase concentrations have been measured by highly sensitive tunable diode laser spectrometry, whereas the liquid phase has been analyzed by ion chromatography. At 298 K the Henry's law constant of HONO in sulfuric acid is well described for H2SO4 concentrations < 53 wt % by KH = (47.2 ± 2.8) exp[(−0.044 ± 0.002) cH2SO4] mol kg-1 bar-1, with cH2SO4 in wt %. The exponential dependence of KH on cH2SO4 that has been observed with increasing H2SO4 concentration is explained by the Setschenow equation. The values of ΔHsol and ΔSsol for the dissolution of HONO have been determined as a function of sulfuric acid concentration. The results were fitted to a four-parameter equation that allows the calculation of the effective solubility of HONO in the temperature and concentration ranges studied. In addition, the equilibrium between HONO and NO+ is discussed.