Question

Which of the noble gases has the highest density at standard temperature and pressure ?

Answer 1

Ans. Noble gases include –

            He – Molar mass = 4.00 g/ mol

            Ne – Molar mass = 20.18 g/ mol

Ar – Molar mass = 39.45 g/ mol

Kr – Molar mass = 83.80 g/ mol

Xe – Molar mass = 131.29 g/ mol

Rn – Molar mass = 222.0 g/ mol

At STP, 1 mol of all gases (ideal) occupy a volume of 22.414 L/ mol.

# Density of gas at STP = Molar mass / Molar volume at STP       - equation 1

Note that, greater is the molar mass of a gas in equation 1, greater would be its density at STP because the molar volume remains constant at 22.414 L/mol

For example-

            Density of He = (4.00 g/ mol) / (22.4 L /mol) = 0.1786 g/ L

            Density of Kr = (83.80 g/ mol) / (22.4 L /mol) = 3.7411 g/ L

            Density of Rn = (222.0 g/ mol) / (22.4 L /mol) = 9.9107 g / mol

Therefore, Rn has highest density at STP.