Question

Air is approximately 79% nitrogen and 21% oxygen by volume. How many moles of oxygen are present in 22.0 L of 24 C and a pressure of 53 kPa?

Answer 1

According to Dalton's law of partial pressure, the total pressure of the system is

`P_t = n_t((RT)/V)`

Convert given units into appropriate units for the gas equations:

`24 ^oC = 297 K`

and

`53 kPa = 0.52 atm`

The total moles in the system:

`n_t = ((0.52 atm)(22.0 L))/((0.08206 (L-atm)/(mol-K))(297 K)) = 0.47 mol`

So, using mole fractions of each molecule,

`mol_(N_2) = (0.79)(0.47 mol) = 0.37 mol_(N_2)`

and

`mol_(O_2) = (0.21)(0.47 mol) = 0.099 mol_(O_2)`