college chemistry 1

Question

Complete combustion of  8.60g of a hydrocarbon produced 27.5 g of CO2 and 9.84 g of H2O. What is the empirical formula for the hydrocarbon? Insert subscripts as necessary.

Answer 1

Convert g to moles:

27.5 g CO2 x 1 mol CO2/44 g = 0.625 moles CO2 x 1 mol C/mol CO2 = 0.625 moles of C

9.84 g H2O x 1 mol H2O/18 g = 0.547 moles H2O x 2 mol H/mol H2O = 1.09 moles of H

Now we try to get whole numbers for the moles, so we divide both by 0.625 to make mol C = 1....

moles C = 0.625/0.625 = 1.0 mol C

moles H = 1.09/0.625 = 1.74 mol H

Now we can multiply both by 4 to get whole numbers...

1.0 mol C x 4 = 4 moles C

1.74 mol H x 4 = 7 moles H

Empirical formula = C₄H₇ (not sure what this is, but this is what I came up with for empirical formula)