Chemistry Practice Problems Henry's Law Practice Problems Solution: The partial pressure of O2 in air at sea level is ...

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Solution: 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 .

Problem

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 .

Solution

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=kH·Pgas


where:

 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, kof O2 based on the given solubility and pressure at 20 oC using Henry's Law

Step 2Calculate the mole fraction of O2 in the air at the mountain lake 

Step 3Determine 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 


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