A75.0 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?

 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