Question

A 75.0 l steel tank at 20.0°c contains acetylene gas, c2h2, at a pressure of 1.39 atm. assuming ideal behavior, how many grams of acetylene are in the tank?

Answer 1

 we can use the ideal gas law equation to find the number of moles of acetylene gas in the tank 
PV = nRT
where 
P - pressure - 1.39 atm x 101 325 Pa/atm = 140 842 Pa
V - volume - 75.0 x 10⁻³ m³
n - number of moles 
R - universal gas constant - 8.314 Jmol⁻¹K⁻¹
T - temperature in kelvin - 20 °C + 273 = 293 K
substituting these values in the equation 
140 842 Pa x 75.0 x 10⁻³ m³ = n x 8.314 Jmol⁻¹K⁻¹ x 293 K
n = 4.34 mol
molar mass of acetylene - 26 g/mol 
mass of acetylene present - 4.34 mol x 26 g/mol = 112.84 g
mass of acetylene present - 112.84 g