Which gas has the higher solubility CO2 or O2?

Answer 1

Short answer:

If water is the solvent and the temperature and pressure are near normal (1 atmosphere pressure, 77 F or 25C temperature) then CO2 is about 25 times more soluble than O2 on a volumetric basis and 40 times as soluble on a mass basis.

Detailed answer:

You question should be more specific since the solubility of a gas in another substance depends on what that substance is, what the temperature of the system is and what the pressure of the gas is.

However, if I assume that the solvent is pure water, that the temperature of the system is about room temperature (25C or 77F) and that the pressure is 1 atmosphere then a calculation is possible using Henry's Law:

P = K * X

where

P is the partial pressure of the gas

K is the Henry's Law constant

X is the molar concentration of gas in the liquid (in Moles/Liter)

For some gases, like CO2, the Henry's Law constant will vary greatly with temperature making the calculation more complex. Most gases also deviate slightly from ideal Henry's law behavior when the concentration becomes large or the pressures extreme.

In the textbook "Physical Chemistry 3rd Edition" by P.W. Atkins on pg 168 the Henry's law constant for O2 at 298 K (25C or 77F) is given as 3.3 x 10^7 Torr while CO2 is given as 1.25 x 10^6 Torr. If we assume pure gas at atmospheric pressure (equal to 760 Torr) and calculate X we get

CO2: X = P/K = 760/1.25*10^6 = 0.000608 (6.08e-4) moles CO2 / liter water

That works out to 0.02918 grams per liter of water

O2: X = P/K = 760/3.3*10^7 = 0.000023036.08 (2.304e-5) moles O2 / liter of water

That works out to 0.000737 grams per liter of water

So at atmospheric pressure with a pure water solvent at 77 F (25 C) carbon dioxide is 26.4 times as soluble on a volumetric basis (liters of solute per liter of water) or 39.6 times as soluble on a mass basis (grams of solute per liter of water)