The mole fraction of oxygen molecules in dry air is 0.2095.
Daltons Law:
Po2/90=.2095
Po2=18.8 kPa
This is a follow up from yesterday, how did you get the mole fraction? I don't get it
Bob Pursley answered your question yesterday. The mole fraction of gases is the percent; i.e., oxygen is about 21% oxygen so the mole fraction is 0.21.
pO2 = XO2 x Ptotal
To calculate the mole fraction of a specific component in a mixture, follow these steps:
1. Determine the number of moles of the component: In this case, we need to find the number of moles of oxygen molecules in dry air.
2. Calculate the total number of moles in the mixture: Dry air is composed of several gases, including nitrogen, oxygen, carbon dioxide, and trace amounts of other gases. To find the total number of moles in the mixture, you can use the ideal gas law equation:
PV = nRT
where:
P is the pressure of the gas (in this case, the atmospheric pressure)
V is the volume of the gas (you can use a standard volume, such as the volume of a container at standard conditions)
n is the number of moles
R is the ideal gas constant (approximated as 0.0821 L·atm/(mol·K) for this calculation)
T is the temperature of the gas
Since the volume, temperature, and pressure are constant for dry air, you can simplify the equation to:
n = P / (RT)
3. Determine the mole fraction: Divide the number of moles of the specific component (in this case, oxygen molecules) by the total number of moles in the mixture.
mole fraction (X) = moles of the component / total moles in the mixture
In the given problem, the mole fraction of oxygen molecules in dry air was provided as 0.2095. This means that 20.95% of the total moles of gas in dry air are oxygen molecules.
Using Dalton's law of partial pressures (which states that the total pressure of a mixture of ideal gases is equal to the sum of the partial pressures of each individual component), you can calculate the partial pressure of oxygen (Po2) using the given mole fraction (X) and the atmospheric pressure (which is typically around 101.3 kPa):
Po2 = X × atmospheric pressure
= 0.2095 × 101.3 kPa
≈ 18.8 kPa
Thus, the partial pressure of oxygen in dry air is approximately 18.8 kPa.