Calculate the Partial pressure of each gas at STP, and calculate the density at STP.

Question

At STP, air can be considered to be a mixture of ideal gases: 21.1% O₂, 78.0% N₂ and 1.00% Ar by volume.

 

a) Calculate the partial pressure of each gas at STP.

This is what I've come up with:

X_N2= 21.1/100 = 0.211 x 1atm = 0.211 atm

X_O2= 78.0/100 = 0.780 x 1atm = .780 atm

X_Ar= 1.00/100 = 0.0100 x 1atm = 0.0100 atm

 

b) calculate the density of air in g/L at STP.

 

 

Answer 1

You are correct for part (a).  For part (b), recall the density is mass/volume.  You can assume you have 1 L volume of gas. From the mole fractions of each gas (0.211, 0.780 and 0.01 for N2, O2 and Ar respectively), you can find the mass of each. Add the masses together to get total mass, and divide by the volume of 1 L to get density in g/L.