[oddone]

A hydrocarbon is 80% carbon and 20% hydrogen and has a density of 1.34 g/liter at STP. What is the molecular mass of this substance?


I know I have to get from g/L to g/mole.
If there is 80 g C then there will be 20 g H. So there will be 6.67 M C and 19.8 M H.
Where do I go from here?

[rabolisk]

Now you go from density (1.34 g/L) to molecular mass. You actually don't need to know anything about the composition of the hydrocarbon, because the question isn't asking you to determine the molecular formula of the hydrocarbon. There is a direct route from density to molecular mass of any ideal gas. You can use the ideal gas law with some rearrangements.

[oddone]

Thank you! I was definitely over thinking this.

1.34 g/L * 22.414 L= 30. g