A gas consists of 85.7 % carbon and 14.3% hydrogen, by weight. A sample of this gas
weighing 0.673 g occupies 729 mL at a pressure of 720.0 mmHg and a temperature of
77°C. Calculate its empirical and molecular formulas.

answer: CH2, C2H4

Can someone explain how to get this answer?

Question

A gas consists of 85.7 % carbon and 14.3% hydrogen, by weight. A sample of this gas 
weighing 0.673 g occupies 729 mL at a pressure of 720.0 mmHg and a temperature of 
77°C. Calculate its empirical and molecular formulas.

answer: CH2, C2H4

Can someone explain how to get this answer?

anonymous · Answer

http://answers.yahoo.com/question/index?qid=20091008010922AAOaDyb

anonymous · Answer

To start these off, I always assumed I had a 100g sample of whatever was here. That left me with 85.7 g of carbon and 14.3g of hydrogen. From there, use the ideal gas law (PV=nRT) to determine the number of moles of substance you have (you're given the pressure, the volume, the temperature (convert to Kelvin), and the ideal gas constant you can look up (make sure your units are right)). Well, looks like i got beat to the punch on the ending, so follow Yahoo answers for the last part :) hope we helped