Henry's law coefficients of formic and acetic acids

The Henry's law constants, K_H, of dilute aqueous formic and acetic acids were determined experimentally as a function of concentration and temperature using a new counterflow packed-column technique. K_H was found to be (8.9±1.3)×10³ and (4.1±0.4)×10³ M atm^-1 at 25°C for HCOOH and CH₃COOH, respectively. The reaction enthalpies, H, were found to be –51±2 kJ mol^-1 and –52±1 kJ mol^-1 for formic and acetic acid, respectively. These are in good agreement with calculated thermochemical values.Whereas the K_H values are in reasonably good agreement with certain other experimentally determined values, K_H (HCOOH) is two to three times higher than calculated thermochemical values while K_H (CH₃COOH) is lower than the two calculated values.The best experimental values appear to be (11±2)×10³ M atm^-1 and (7±3)×10³ M atm^-1 for HCOOH and CH₃COOH, respectively.