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 ran ge 0.3-73.6 wt % and temperature between 248 and 298 K by measuring th e distribution of HONO between the gas and liquid phases using a bubbl er-type gas-liquid reactor. Gas phase concentrations have been measure d by highly sensitive tunable diode laser spectrometry, whereas the li quid 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 c oncentrations < 53 wt % by K-H = (47.2 +/- 2.8) exp[(-0.044 +/- 0.002) C-H?2SO?4] mol kg(-1) bar(-1), with c(H2SO4) in wt %. The exponential dependence of K-H on C-H2SO4 that has been observed with increasing H 2SO4 concentration is explained by the Setschenow equation. The values of Delta H-sol and Delta S-sol for the dissolution of HONO have been determined as a function of sulfuric acid concentration. The results w ere 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.