How do you find the molecular mass and formula using gas densities?

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Gas densities can be used to estimate molecular mass and determine molecular formulas by applying the Ideal Gas Law (PV=nRT). At standard temperature and pressure (STP), one mole of gas occupies 22.4 liters. By knowing the density of a gas in grams per liter, one can calculate the mass of gas needed to fill this volume, leading to the determination of grams per mole, or Gram Molecular Weight. If density is provided at different temperature and pressure conditions, it can be recalculated for STP. However, it is important to maintain clarity in terminology, as "grams" should not be conflated with "mass." Instead of recalculating density for STP, one can directly calculate the volume of one mole of gas under the given conditions to find the corresponding mass.
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How does one use ratios of gas densities to estimate the molecular mass and find the molecular
formulas?
 
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Conceptually keep in mind Ideal Gas Law PV=nRT can allow one to show that at STP one mole of gas molecules exist in 22.4 liters of volume.
since gas density is gms/ liter (mass/volume) one can calculate the gms of gas from the density to make 22.4 liters or one mole of gas... gms per mole then gives a Gram Molecular Weight

If the density is given at a different temperature and pressure recalculate it for STP
 
MrSid said:
Conceptually keep in mind Ideal Gas Law PV=nRT can allow one to show that at STP one mole of gas molecules exist in 22.4 liters of volume.
since gas density is gms/ liter (mass/volume) one can calculate the gms of gas from the density to make 22.4 liters or one mole of gas... gms per mole then gives a Gram Molecular Weight

You are right, but mixing mass and "grams of gas" in one sentence is not a good idea. "Grams" are not a synonym of "mass".

If the density is given at a different temperature and pressure recalculate it for STP

No need for that - you can calculate volume of 1 mole of gas for these conditions and use this volume to calculate mass of 1 mole.
 

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