Question

240 ml of a dry gas measured at 27c and 750mm pressure weighs 0.64g. Calculate the molecular weight of the gas.

Answer 1

Molecular weight of gas is - 71.1 g

To calculate molecular weight, ideal gas equation will be used.

Ideal gas law or equation is equation derived by combining Boyle's law, Charles law and Avogadro's law.

Ideal gas equation is -

PV = nRT

P denotes pressure, v denotes volume, n is for number of moles, R is gas constant and t represents temperature.

Given values in question are -

P = 750mm

V = 240 ml = 0.24 l

T = 27 °C = 273+27 = 300 K

Number of moles = weight/molecular weight

Weight = 0.64g

R = 62.363 mm L/mol/K

Keeping values in equation -

N = PV/RT

N = 750*0.24/(300*62.363)

N = 0.009

N = weight/molecular weight

Molecular weight = 0.64/0.009

Molecular weight = 71.1 g