Question

A sample of argon gas at stp occupies 56.2 liters. determine the number of moles of argon and the mass in the sample. for the above problem how will you rearrange the ideal gas law to solve for moles of argon?

Answer 1

We can use the ideal gas law equation to find the number of moles;
PV = nRT
where P - pressure
V - volume - 56.2 x 10⁻³ m³
n - number of moles
R - universal gas constant - 8.314 Jmol⁻¹K⁻¹
T - temperature 
standard temperature is 273 K
and standard pressure - 101 325 Pa
we can rearrange the equation to find the number of moles 
$n = \frac{PV}{RT}$
substituting the values in the equation 
$n = \frac{101325Pa*56.2 x 10⁻³ m³}{8.314 Jmol⁻¹K⁻¹*273K}$
n = 2.51 mol 
molar mass of Ar - 40 g/mol
mass of Ar in the sample - 2.51 mol x 40 g/mol = 100.4 g