Ideal Gas Equation  Problem regarding mass
Hi people, I needed some assistance with this problem I came across that involved the use of the ideal gas equation.
Q. A gas cylinder has a volume of 20 litres (20*10^3 m^3). It contains air at a temperature of 17 degrees Celsius and an excess pressure of 3.0*10^5 Pa above the atmospheric pressure 1.0*10^5 Pa. Calculate the mass of air in the cylinder, given that the density of air at STP is 1.3 kg/m^3.
A. 98*10^3 kg.
My attempted solution at this was:
PV = nRT
By using the equation above we can work out the number of moles "n". So rearranging to make n the subject of the formula.
n = PV/RT
Therefore n = (4*10^5 N/m^2)(20*10^3 m^3)/(8.31 J/kg*K)(290 K)
We get n to be 3.32 (correct to 3 s.f.)
Since n is also = m/Mr
Where m is the mass in kg and Mr is the molar mass.
m = n*Mr = (3.32)(0.029) = 0.09628 kg
As you can you can see I failed to arrive at the correct answer, and I am unsure why we have been provided the density of air at STP?
I would appreciate any help, thank you in advance!
