Chemistry Question...Empirical Formula?

Question

Many homes in rural America are heated by a propane gas, a compound that contains only carbon and hydrogen. Complete combustion of a sample of propane produced 2.641g of carbon dioxide and 1.442g of water as the only products. Find the empirical formula of propane.

Answer 1

First realize that all the molecules combine atoms in fixed ratios, based on molecular mass

In 2.641g of CO2, there is 12 / 44 of C and 32 / 44 of O

the 1.442g of water has 2 / 18 of H and 16 / 18 of O

Now that you have the grams of C and H,
divide those by the molecular mass of each atom and calculate the empirical formula in the normal way

Answer 2

2.641 g CO2 contains 2.641x(12.011/44.011) = 0.7208g Carbon (0.7208g/12.011=0.0600 moles of C)
1.442g H2O contains 1.442 x(2.016/18.016)=0.1614g Hydrogen (0.1614/1.008=0.1601 moles of H atoms)

C:H=0.0600 : 0.1601 = 1 : 2.67 (x3 to get whole numbers = C3H8)
empirical formula = C3H8