Question

The empirical formula of a compound is CH₂.  At 373 K, 35.28 g of this gas occupies 2.00 L at a pressure of 6.43 atm.  

What is the molecular formula of this compound ?

Answer 1

Ideal gas equation:
PV = nRT
Here,
P is pressure
V is volume
n is number of moles
R is gas constant
T is temperature

------

n = PV / RT

n = (6.43 atm × 2.00 L) / ( 0.0821 L.atm / mol.K × 373 K)

n = 0.4199 mol

n = mass / molar mass

Molar mass = mass / n

Molar mass = 35.28 g / 0.4199 mol

Molar mass = 84.02 g/mol

Molecular formula = (emperical formula)_n

n = molecular formula mass / empeicaem formula mass

n = 84.02 / 14.03

n = 5.99

n = 6

Hence molecular formula = (CH2)₆ = C_{​​​​​​6}​​​​H_{​​​​12}