A sample of a mixture containing an unknown hydrocarbon and some nitrogen dioxide, NOx, had a total mass of 31.25 grams. The mixture was analyzed using combustion analysis, producing 78.44 g of carbon dioxide, CO2, and 32.12 g of water, H20. a) Calculate the empirical formula of the hydrocarbon.

b) The molar mass of the compound was found to be 252.48 g/mol. What is the molecular formula of the hydrocarbon?

c) What percentage (by mass) of the original sample was the hydrocarbon?

a) CH2

b) C18H36

c) 80%

Explanation:

CO2 = 44.009 g/mol  --> 78.44 g = 1.782 mol of CO2

H2O - 18.015 g/mol --> 32.12 g = 1.782 mol of H2O

a) 1.782 mol of CO2 contain 1.782 mol of C, 1.782 mol of H2O contain 1.782 x 2 mol of H

Thus, Emperical formulae of Hydrocarbon = CH2

b) CH2 = 14.027 g

252.48g / 14.027 g = 18

Molecular formulae of Hydrocarbon = C18H36

c) 1.782 mol of CH2 was combusted

1.782 x (14.027 g) = 24.996 g

% of sample equaling HydroCarbon = 24.996 g/31.25 g = 79.98 % = 80 %

c, liquids evaporate, creating a gas

the answer is d. 74.02