We’re being asked to calculate the molar concentration of O2 in the surface water of a mountain lake saturated with air at 20 oC and an atmospheric pressure of 670 torr.
Recall that the solubility of a gas is given by Henry’s law:
Sgas = solubility of the gas (in mol/L or M)
kH = Henry’s law constant for the gas
Pgas = partial pressure of the gas
For this problem, we need to do the following steps:
Step 1: Calculate the Henry’s Law constant, kH of O2 based on the given solubility and pressure at 20 oC using Henry's Law
Step 2: Calculate the mole fraction of O2 in the air at the mountain lake
Step 3: Determine the partial pressure of O2 at the mountain lake from the given atmospheric pressure
Step 4:Calculate the molar concentration or solubility of O2 in the surface water
The partial pressure of O2 in air at sea level is 0.21 atm . The solubility of O2 in water at 20 oC , at 1 atm gas pressure, is 1.38 10-3 M (from Table 13.1 in your textbook).
Using Henrys law and the data in the introduction, calculate the molar concentration of O2 in the surface water of a mountain lake saturated with air at 20 oC and an atmospheric pressure of 670 torr .
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