Solubility of Gases in Liquids. 22. High­precision Determination of Henry Constants for Oxygen in Liquid Water from T = 274 to 328 K

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The solubility of oxygen in pure liquid water was measured at a total pressure of about 100 kPa and from about T = 274.15 K to T = 328.14 K using an analytical method characterized by a precision of ± 0.05 per cent or less. From the experimental results, Henry’s law constants H2,1(T, ps,1) at the vapor pressureps,1 (T) of water as well as the Ostwald coefficientsL2,1 at infinite dilution were obtained via a rigorous thermodynamic method. Measurements were made at roughly 0.5 K intervals around T = 277.15 K, that is, around the temperature of the maximum density of water, between T = 274.15 K andT = 281.14 K (region I), and at roughly 5 K intervals aboveT = 283.17 K (region II). For each region, the data ln{H2,1 (T, ps,1) / Pa } were fitted to a three-term power series in 1 / T: the average percentage deviation of the experimental Henry’s law constants in region I is 0.013, while for region II 0.051 is obtained. The average percentage deviation of the entire set of measured Henry’s law constants (32 points), extending from T = 274.15 K toT = 328.14 K, is 0.039. Similar results are obtained for the Ostwald coefficients. Subsequently, the partial molar enthalpy changes on solution and the partial molar heat capacity changes on solution were obtained from the temperature dependence of the Henry’s law constant (van’t Hoff analysis). Agreement with calorimetrically determined quantities is excellent. We believe that our new values for the Henry’s law constantH2,1 (T, ps,1) and the Ostwald coefficientL2,1 of oxygen in water are the most reliable ones to date.