Physics
posted by Johnson .
An apartment has a living room whose dimensions are 2.5 m 4.8 m 5.9 m. Assume that the air in the room is composed of 79% nitrogen (N2) and 21% oxygen (O2). At a temperature of 27°C and a pressure of 1.01 105 Pa, what is the mass (in grams) of the air?
Ideal gas formula is pv=nrt,but the problem is asking me to find the mass?

Compute the number of moles n first. You can then say that:
n = n_{N2} + n_{O2}
You also know that:
n_{N2}/n = 0.79
and
n_{O2}/n = 0.79
This allows you to solve for n_{N2} and n_{O2}. Using the molar masses for N2 and O2 you can then obtain the mass. 
Air is a mixture of nitrogen, oxygen, and other gases.
At STP, one mole of an ideal gas occupies 22.4 liters.
Assume air is 21% O2 and 79% N2 by volume
0.21 x 32 g/mol + 0.79 x 28 g/mole = 28.8 g / mol of "air"
28.8 g / 22,400 mL = 0.0013 g/mL