Talk:Oxygen solubility

Numerical examples for oxygen solubility and the activity of dissolved oxygen

The numerical examples include the following constants:

• (c) The volume fraction of oxygen in dry air is constant at 0.20946.
• (d) The saturation water vapour pressure at 25 °C is 3.17 kPa. The partial pressure of oxygen in water vapour saturated air at 25 °C and barometric pressure of 100 kPa is (100-3.17)·0.20946 = 20.28 kPa. The oxygen solubility in pure water at 25 °C is 12.56 µM/kPa.
• (e) The saturation water vapour pressure at 37 °C is 6.27 kPa. The partial pressure of oxygen in water vapour saturated air at 37 °C and barometric pressure of 100 kPa is (100-6.27)·0.20946 = 19.63 kPa. The oxygen solubility in pure water at 37 °C is 10.56 µM/kPa.
• (f) The oxygen solubility factor of the medium MiR05 relative to pure water is 0.92 at 25 °C and 37 °C.

1. An aqueous solution of pure water in equilibrium with air at standard barometric pressure (100 kPa) is heated from 25 °C to 37 °C, maintaining equlibrium between the aqueous and gaseous phase. The concentration of dissolved oxygen changes from 254.7 µM at 25 °C to 207.3 µM at 37 °C. The partial pressure of oxygen changes from 20.3 to 19.6 kPa. The relative activity of oxygen is 20.3 and 19.6, corresponding to the specific activity in the pressure format [20.3 to 19.6 kPa] or the specific activity in the concentration format (20.3 to 19.6 µM].
2. An aqueous solution of pure water in equilibrium with air at standard barometric pressure (100 kPa) changed from pure water to a physiological salt solution (MiR05) at 37 °C. The concentration of dissolved oxygen changes from 207.3 µM in pure water to 190.7 µM in MiR05. The partial pressure of oxygen remains constant at 19.6 kPa. Therefore, the relative activity of oxygen is 19.6, corresponding to the specific activity in the pressure format [19.6 kPa] or the specific activity in the concentration format (19.6 µM] in both media maintaining equilibrium with the gas phase.
3. An aqueous solution (MiR05) in equilibrium with air at standard barometric pressure (100 kPa) and 25 °C is heated in a closed system from the initial temperature of 25 °C to 37 °C. The concentration remains constant at 234.4 µM, since oxygen cannot be exchanged across the boundaries of the closed system. The partial pressure of oxygen is initially 20.3 kPa at 25 °C (234.4/11.56). The partial pressure increases upon heating to 37 °C in the closed system to 24.1 kPa (234.4/9.72). The relative activity of the gases in solution leads increases to >100 kPa, which leads to gas bubble formation, if the closed system is maintained at constant barometric pressure, as is the case in a respirometer with a chamber that is closed by a stopper with a titration capillary (through which the barometric pressure is kept constant).

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