Determination of Henry’s constant using a photoacoustic sensor

We present a simple method for measuring Henry’s constant k H of ethanol using photoacoustic spectroscopy. At T = 298.1 K the measured value fork H is (0.877 ± 0.039)kPa · kg · mol −1 . Our data show that Henry’s law is valid at ethanol molalities between 0.1mol · kg −1 and 1.4 mol · kg −1 . The temperature dependence of Henry’s constant was carefully examined by measuring the ethanol vapour pressure of six different aqueous solutions between T = 273.1 K and T = 298.1 K. By analysing the gas phase concentration and applying Henry’s law, an ethanol molality of 0.864 mol · kg −1 in the liquid phase can be measured with an error of ±0.038mol · kg −1 . The detection limit of the photoacoustic sensor is a gaseous ethanol pressure of 10 −3kPa. Ethanol molality changes as low as 1.10 −3mol · kg −1 can be measured.