Question

What is the molar mass of 81.50g of gas exerting a pressure of 1.75atm on the walls of a 4.92L container at 307K?

Answer 1

M = 81.50g, mm = m/n
n = ???
PV = nRT --> n = PV/RT
n = (1.75)(4.92)/(.0821)(307)
n = 8.61/25.20 = .342
--> mm = m/n = 81.5/.342 = 238.58

Answer 2

Answer: Molar mass of gas is 238.6 g/mol

Explanation:

Using ideal gas equation:  

PV = nRT

P= pressure = 1.75 atm

V= volume = 4.92 L

n = no of moles =$\frac{\text {given mass}}{\text {Molar mass}}=\farc{81.5}{M}$

R= gas constant =0.0821 Latm\molK

T = temperature = 307 K

R= gas constant = 8.314 J/Kmol

T= temperature = 190.7 K

M= molecular mass of gas = ?g/mol

$1.75\times 4.92=\frac{81.5}{M}\times 0.0821\times 307$

$M=238.6g/mol$