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Talk:Oxygen solubility

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Calculations

Fundamentals in short

The ideal gas law plays a central role in elucidating the behavior of gases dissolved in aqueous solution, where O2 interacts with a very different environment compared to the gas phase.
Eq. 1:  cG(g) = pG路(RT)-1 
The gas law (Eq. 1) is called 'ideal', since the activity coefficient G(g) of an ideal gas G is defined as zero. Actually, the molar volume Vm,G(g) = 1/cG of the ideal gas is 22.414 L/mol at 0 掳C, whereas the real molar volume of O2 is Vm,O2(g) = 22.392 L/mol at 0 掳C. The ratio Vm,G(g)/Vm,O2(g) is O2(g) = 22.414/22.392 = 1.001. Therefore, O2(g) behaves closely as an ideal gas at practically encountered barometric pressures. In aqueous solution, O2(aq) has a much higher activity coefficient O2(g). Defining solubility as concentration per pressure, rearranging Eq. 1, and inserting the activity coefficient O2(aq) yields,
Eq. 2a:  SG(g) = cG(g)路pG-1 = (RT)-1


Eq. 2b:  O2(aq)路SO2(aq) = O2(aq)路cO2(aq)路pO2-1 = (RT)-1 
The partial pressures of a gas in the gas phase and aqueous phase are equal at equilibium between the two phases. Pressure is general at practically encountered pressures (fugacity is the more general concept applicable in the deep sea), such that the partial pressure of an ideal gas pG can be set equal to the partial pressure of a real gas pO2. Therefore, O2(aq) is derived as
Eq. 3:  O2(aq) = cG(g)/cO2(aq) = SG(g)/SO2(aq) 


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