Question

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.

Answer 1

The effective molar mass of air at STP is 28.82 g/mol.

Step-by-step explanation:

At STP, the value of pressure is 1 atm.

At STP, the temperature is equal to 273.15 K

P = 1atm, T = 273.15 K

Density of the gas at STP ,d= 1.285 g/L

`PV=nRT` (Ideal gas equation)

`PV=\frac{\text{Mass of air}}{\text{Molar mass of air(M)}}RT`

`Density=(Mass)/(Volume)`

`P* M=d* RT`

`M=(1.285 g/L)/(1 atm)* 0.0821 atm L/mol K* 273.15 K`

M = 28.81 g/mol

The effective molar mass of air at STP is 28.82 g/mol.