Density and Molecular Mass Calculations

The Ideal or Universal Gas Law can also be used to calculate the density or molecular mass (mass of 1 mol) of a gas. A convenient equation has been derived to make calculations a breeze (no pun intended!)



  • D= Density
  • P= Pressure
  • R= Ideal Gas Constant (0.0821 Latm/molK)
  • M= Molecular Mass of gas
  • T= Temperature

HINT: You may not be given density, but be resourceful. If you have the mass and volume of the gas instead, use the density equation and you’re in business!

NOTE: Also note that since this a variation of the Ideal Gas Law, you will still be using “R,” which means that all units must be SI!

Problem: A 2.10-L vessel contains 4.65 g of a gas at 1.00 atm and 27.0°C. What is the molar mass of the gas?




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