A gas analysis on a gaseous mixture gives 60% methane and 40% ethylene by volume. You need to store 12.3 kg of the mixture in a cylinder of volume 0.0514 m^3 at a maximum temperature of 45°C. Determine the pressure (kPa) inside the cylinder by: a. assuming that the mixture obeys ideal gas law b. using the compressibility factor method I approached part a of this problem by taking both 60 and 40 percent of 12.3 kg to find the mass of the methane and ethylene, respectively in the ideal gas mixture. A friend has informed me that this is not the proper approach because 60% and 40% are percentages by volume, not mass fractions, and therefore he recommended that I should instead take 60% and 40% of the molar masses of methane and ethylene instead. I don't understand what percent volume has to do with molar mass. Why would I multiply the percentage by volume times the respective molar masses if I want to find the number of moles methane and ethylene in the compound?