Question

O2 gas is most soluble at

a) top of a lake.

b) bottom of a lake.

c) all levels since solubility is unaffected by the depth level.

Answer 1

The correct answer is option (b). bottom of a lake.

This can be explained using Henry's law which states that "the solubility of a gas in a liquid is directly proportional to the partial pressure of the gas in the vapor phase."

So as the depth of a lake increases, the total pressure also increases which is the sum of atmospheric pressure (at the surface of the lake) plus gauge pressure i.e., the pressure due to the column of water of the lake. The gauge pressure is equal to hρg where h is the depth of the lake, ρ is the density of water and g = 9.8 m/s^{​​​​​​2}.

Hence as the depth of a water source increases, the solubility of O_{​​​​​​2} (infact all atmospheric gases) in the water also increases.