A compound with the empirical formula NPCl2 was found in a subsequent experiment to have a molar mass of 347.64 g/mol. What is the molecular formula of the compound?

                     Molecular Formula  =  N₃P₃Cl₆

Explanation:

Molecular formula is calculated by using following formula,

                    Molecular Formula  =  n × Empirical Formula   (1)

Also, n is given as,

                     n  =  Molecular Weight / Empirical Formula Weight

Molecular Weight  =  347.64 g.mol⁻¹

Empirical Formula Weight  =  1 (N) + 1 (P) + 2 (Cl)  =  115.88 g.mol⁻¹

So,

                     n  =  347.64 g.mol⁻¹ ÷ 115.88 g.mol⁻¹

                     n  =  3

Putting Empirical Formula and value of "n" in equation 1,

                    Molecular Formula  = 3 × NPCl₂

                    Molecular Formula  =  N₃P₃Cl₆

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.