Solubility of Nitrous Acid (HONO) in Sulfuric Acid Solutions

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 H 2 SO 4 concentrations < 53 wt % by K H = (47.2 ± 2.8) exp[(−0.044 ± 0.002) c H 2 SO 4 ] mol kg -1 bar -1, with c H 2 SO 4 in wt %. The exponential dependence of K H on c H 2 SO 4 that has been observed with increasing H 2 SO 4 concentration is explained by the Setschenow equation. The values of Δ H sol and Δ S sol 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.