Critical evaluation of the 2nd dissociation constants for aqueous sulfuric acid

Six different equations for the second dissociation reaction constant (K2) for sulfuric acid were tested using four different Pitzer parameter sets, including two four parameter and two five parameter sets. The best considered electrochemical cell data between 0 and 50 °C and water activity data at 25 °C were used in fitting the total number of 24 evaluations. Most of the considered equations are able to fit the data within assumed experimental accuracy. A set of four Pitzer parameters with temperature dependency a + b/T is required to present the activity and osmotic coefficient data. The predicted stoichiometric osmotic coefficients at temperatures 0, 25 and 50 °C agree well with more complicated models presented in the literature for sulfuric acid–water system. One of the studied K2 equations was able to extrapolate the stoichiometric osmotic coefficient within 0.01 up to 140 °C.