What is the density of helium gas at 17°C and 773 torr?

Question

Quizplus · Accepted Answer

Using the ideal gas law, PV = nRT, we can calculate the number of moles of helium gas present:
n = PV/RT = (773 torr)(V)/(0.08206 L·atm/mol·K)(17+273 K)
The units of torr cancel out and we convert liters to cubic meters:
n = (773/760 × 101325 N/m²)(V)/(8.314 J/mol·K)(290 K) = 0.03126 V
The mass of helium gas can be calculated from the number of moles and the molar mass, M = 4.00 g/mol:
m = nM = 0.1250 V g
Finally, we can calculate the density of helium gas:
ρ = m/V = 0.1250 g/V
ρ = (0.1250 g/L)(1 L/1000 mL)(1000 mL/1 L) = 0.1250 g/1000 mL = 0.125 g/L
ρ = 0.171 g/L (rounded to three significant figures)

What Is the Density of Helium Gas at 17°C and 773