A gas consists of 85.7 % carbon and 14.3 % hydrogen, by weight. A sample of this gas weighing 0.673 g occupies 729 mL at a pressure of 720.0 mmHg and a temperature of 77°C. Calculate its empirical and molecular formulas.

Question

Quizplus · Accepted Answer

1) Calculate the number of moles of gas: (0.673 g)/(12.01 g/mol + 1.008 g/mol) = 0.0500 mol 2) Use the ideal gas law to calculate the number of moles if the gas were at standard temperature and pressure (STP): PV = nRT (720.0 mmHg)(0.729 L) = n(0.08206 L atm/mol K)(350 K) n = 0.0325 mol 3) Calculate the empirical formula: Carbon: (0.857 g)/(12.01 g/mol) = 0.0714 mol Hydrogen: (0.143 g)/(1.008 g/mol) = 0.142 mol Divide by the smallest number of moles to get the empirical formula: C1H2 4) Calculate the molecular formula: Molecular weight = empirical formula weight * n Molecular weight = (12.01 g/mol + 2.016 g/mol) * n Molecular weight = 14.026 mol n = 14.026 g/mol / 0.673 g = 20.8 Round to the nearest integer to get the subscripts in the molecular formula: C1H13₂

A Gas Consists of 85