A welding fuel gas contains carbon and hydrogen only. Burning a small sample of it in oxygen gives 3.38 g carbon dioxide, 0.690 g of water and no other products. A volume of 10.0 L (measured at STP) of this welding gas is found to weigh 11.6 g. Calculate (i) empirical formula, (ii) molar mass of the gas, and (iii) molecular formula.
We can use the given information to determine the empirical formula of the welding gas:
Calculate the no.(number)_ of moles of co2 produced:
n(CO2) = m/M = 3.38 g/44.01 g/mol = 0.0768 mol CO2
Calculate the no of moles of h2o produced:
n(H2O) = m/M = 0.690 g/18.015 g/mol = 0.0383 mol H2O
Calculate the no of moles of C in the sample of the gas:
n(C) = n(CO2) = 0.0768 mol CO2
Calculate the no of moles of hydrogen in the sample of the gas:
n(H) = 2n(H2O) = 20.0383 mol H2O = 0.0766 mol H2O
Calculate the mole ratio of carbon to H in the sample of the gas:
n(C) : n(H) = 0.0768 mol : 0.0766 mol ≈ 1 : 1
Therefore, the empirical formula of the gas is CH.
Next, we can use the given volume and mass of the gas to determine its molar mass:
Calculate the density of the gas at Standrd Temp Pressure:
density = mass/volume = 11.6 g/10.0 L = 1.16 g/L
Calculate the no of moles of the gas in 10.0 L at STP:
n = PV/RT = (1.16 g/L)(10.0 L)/(0.08206 L·atm/mol·K)(273 K) = 0.476 mol
Calculate the molar mass of the gas:
Molar mass = mass/number of moles = 11.6 g/0.476 mol = 24.4 g/mol
Therefore, the molar mass of the gas is 24.4 g/mol.
Finally, we can use the empirical formula and molar mass to determine the molecular formula of the gas:
Calculate the empirical formula mass of the gas:
Empirical formula mass = 12.01 g/mol + 1.01 g/mol = 13.02 g/mol
Calculate the integer multiplier that relates the empirical formula mass to the molar mass:
Integer multiplier = Molar mass / Empirical formula mass = 24.4 g/mol / 13.02 g/mol ≈ 1.87
Multiply the subscripts in the empirical formula by the integer multiplier to obtain the molecular formula:
Molecular formula = C1.87H1.87 ≈ C2H2
Therefore, the molecular formula of the gas is C2H2
Comments
Post a Comment