Question #3973b

1 Answer
Nov 10, 2014

The molar mass for the gas in the example problem is 42 g/(mol)42gmol.


Starting with the definition of molar mass,

molar mass = (grams)/(mol)molarmass=gramsmol

and solve for the number of moles to get the equation

mol = (grams)/(molar mass)mol=gramsmolarmass.

This equation can be substituted into the ideal gas law, PV = nRTPV=nRT, to get

PV=(gRT)/(molar mass)PV=gRTmolarmass

and rearranging this to solve for molar mass gives

molar mass=(gRT)/(PV)molarmass=gRTPV

with this and some simple unit conversions, we can now calculate.

molar mass = (1.62g xx 0.0821 xx 293K)/(0.9842 atm xx 0.941 L) = 42 g/(mol)molarmass=1.62g×0.0821×293K0.9842atm×0.941L=42gmol

Hope this helps.