Jul 13, 2020 · calculate the density of a gas if the mass is 2.94 grams, the volume is 756 mL at 20 C and 500 torr, and the conditions are changed to STP … read more Shirley Oct 22, 2018 · Density Calculations Worksheet - Gallatin County 3) Calculate the mass of a liquid with a density of 2.5 g/mL and a volume of 15 mL. 4) Calculate the volume of a liquid with a density of 5.45 g/mL and a mass of 65 g. Molar mass of a gas. Molar mass is the mass (in atomic mass units) of one mole of a substance. One atomic mass unit (u) is equal to 1/12 the mass of one atom of carbon-12. Thus, the molecular weight of a molecule is the total number of protons and neutrons in all the atoms in that molecule. The molar mass (molecular weight) of Hydrogen is equal to twice its atomic weight (since Hydrogen has 2 atoms - diatomic). In this way, and knowing that the atomic weight of Helium A r (Helium)= 1.008 g/mol, it is easy to calculate the molar mass of Hydrogen , M( Hydrogen ): M( Hydrogen )= A r ( Hydrogen ) * 2= 2.016 g/mol Example Problem: Calculate the work that must be done at standard temperature and pressure (STP is 0°C and 1 atm) to make room for the products of the octane combustion: 2 C 8 H 18 + 25 O 2--> 16 CO 2 + 18 H 2 O Mar 27, 2015 · A mixture contains 5.0 g of He, 1.0 g of Ar, and 3.5 g of Ne. Calculate the volume of this mixture at STP. Calculate the partial pressure of each gas in the mixture at STP. A balloon will burst at a volume of 2.00 L. If it is partially filled at a...