Question

The density of a gaseous compound of phosphorous is 0.943 g\cdotl-1 at 461 k when its pressure is 708 torr. what is the molar mass of the compound? please answer in g/mol.

Answer 1

Based on the ideal gas equation:

PV = nRT----------(1)

P = pressure = 708 torr

V = volume

T = temperature = 461 K

n = number of moles of the gas = mass of gas (m)/Molar mass (M)

R = gas constant = 62.346 Ltorr/molK-1

Equation (1) can also be written as:

PV = (m/M)RT

M = (m/V)RT/P----------(2)

here m/V = density of the gas = 0.943 g/L

Substituting for P, R and T in eq (2) we get the molar mass as:

M = 0.943 * 62.346 * 461/708 = 38.28 g/mol