A 55.50 g gas sample of a gas, at stp, has a volume of 15.0 l. calculate the molecular mass of the gas

Answer is: the molar mass of gas is 82.83 g/mol.

m (gas) = 55.50 g; mass of gas.

V (gas) = 15.0 L; volume of gas.

Vm = 22.4 L/mol; molar volume of gas on STP.

n (gas) = V (gas) : Vm.

n (gas) = 15 L : 22.4 L/mol.

n (gas) = 0.67 mol; amount of gas.

M (gas) = m (gas) : n (gas).

M (gas) = 55.5 g : 0.67 mol.

M (gas) = 82.83 g/mol.

We can use the ideal gas law equation to find the number of moles of gas

PV = nRT

where P - standard pressure - 101 325 Pa

V - volume - 15.0 x 10⁻³ m³

n - number of moles

R - universal gas constant - 8.314 Jmol⁻¹K⁻¹

T - standard temperature - 273 K

substituting the values in the equation

101 325 Pa x 15.0 x 10⁻³ m³ = n x 8.314 Jmol⁻¹K⁻¹ x 273 K

n = 0.670 mol

molecular mass of the gas can be calculated as follows

molar mass = mass / number of moles

= 55.50 g / 0.670 mol

molecular mass of gas is 82.8 g/mol