Chemical speciation effects on the volumetric properties of aqueous sulfuric acid solutions

Densities of fifteen aqueous solutions sulfuric acid (H2SO4) have been measured by vibrating-tube densimetry at solute molalities (m) from (0.01 to 3.0) mol·kg−1 over the temperature range 293.15 ≤ T/K 343.15. These data used calculate corresponding apparent molar volumes Vϕ(H2SO4,aq), which represent a significant expansion volumetric database for this industrially-important acid. At 298.15 K present results agree well with literature data, notably century-old values given in 1926 International Critical Tables. other temperatures, where comparisons are possible agreement Vϕ is also very satisfactory. Consistent earlier studies, Vϕ(H2SO4,aq) was found exhibit an abnormally-large decrease low concentrations (m 0.1 mol·kg−1). This effect consistent change chemical speciation H2SO4(aq), essentially 1:1 electrolyte (H+(aq) + HSO4− (aq)) higher predominantly 1:2 (2H+(aq) SO42− dilute solutions. The were modelled using variants Young’s rule and Pitzer formalism. Combination these standard volume V°(SO42−,aq) enabled estimation V°(HSO4−,aq) change, ΔrV°, first protonation sulfate ion SO42−(aq) → HSO4−(aq)) as functions temperature. It shown that sensitive value constant probably cannot be determined better than ± 0.3 cm3·mol−1 present.