For a certain gas that contains only carbon and hydrogen the mass percentage of carbon is known to be 85.62?

Question

It is also known that 2.58 g of the gas has a volume of 1.00 L and a pressure of 0.980 atm at 50.8 oC.
What is the molecular formula for the gas ?

Answer 1

Find the percentahe of hydrogen first, by subtracting from 100.
Divide each percentage by the Ar of that element, and then divide by the smaller of those answers to get a whole-number ratio. That is the empirical formula.

Now work out n = pV/RT for the gas, remembering to convert to the correct units.

Then calculate the Mr, using the mass given. You can now compare the Mr and the empirical formula to get the molecular formula.