Since air is a mixture,it does not have a "molar mass." However,for calculation purposes,it is possible to speak of its "effective molar mass." (An effective molar mass is a weighted average of the molar masses of a mixture's components.)If air at STP has a density of 1.285 g/L,its effective molar mass is ________ g/mol.
A)26.94
B)31.49
C)30.00
D)34.42
E)28.80

Question

Quizplus · Accepted Answer

The effective molar mass of air can be calculated using the ideal gas law, $PV = nRT$, where $P$ is the pressure, $V$ is the volume, $n$ is the number of moles, $R$ is the ideal gas constant, and $T$ is the temperature. At standard temperature and pressure (STP), $P = 1$ atm, $V = 22.414$ L/mol, and $T = 273.15$ K. Given the density of air at STP is $1.285$ g/L, the mass of 1 mole of air can be calculated as the product of the density and the molar volume at STP, which gives $1.285 \, \text{g/L} \times 22.414 \, \text{L/mol} = 28.80 \, \text{g/mol}$. This calculation approximates the effective molar mass of air by considering its density and the volume occupied by one mole of gas at STP.

Since Air Is a Mixture,it Does Not Have a "Molar