empirical formula:

Question

Complete combustion of 3.60 g of a hydrocarbon produced 11.0 g of CO2 and 5.27 g of H2O. What is the empirical formula for the hydrocarbon? Insert subscripts as necessary.

empirical formula:

Answer 1

Since the unknown is a hydrocarbon, we know it contains only C and H. So we will find the moles of each and then determine the empirical formula.

moles C: 11.0 g CO2 x 1 mol CO2/44 g x 1 mol C / mol CO2 = 0.25 mols C

moles H: 5.27 g H2O x 1 mol H2O / 18 g x 2 mol H / mol H2O = 0.586 mols H

To get whole numbers, let's divide both by 0.25

0.25 / 0.25 = 1 mol C

0.586 / 0.25 = 2.3 mol H

Now we can multiply both by 3 to get all whole numbers of moles

1 x 3 = 3 mols C

2.3 x 3 = 7 mols H

Empirical formula = C₃H₇