Combustion reaction

Question

fuel underwent combustion and 61.64 g of carbon dioxide and 28.39 g of water were produced after the combustion of 20 g of the sample. If the sample contains C and H, what is the sample's molecular formula if it has a molar mass of 114.23 g/mol? is the answer C8H18

Answer 1

Convert grams CO2 H2O to moles of C and H

61.64 g CO2 x 1 mol CO2 / 44 g x 1 mol C / mol CO2 = 1.400 mols C

28.39 g H2O x 1 mol H2O / 18 g x 2 mol H / mol H2O = 3.15 mols H

Divide both mols by 1.400 to try to get whole numbers

1.400/1.400 = 1 mol C

3.15 mols / 1.400 = 2.25 mols H

Multiply both mols by 4 to get whole numbers

1 mol C x 4 = 4 mols C

2.25 mol H x 4 = 9 mols H

Empirical Formula = C₄H₉ with a molar mass of (4x12) +(9x1) = 48 + 9 = 57 g/mol

How many times does 57 g/mol go into 114.23 g/mol? That is 114.23/57 = 2x

Molecular Formula = 2 x C₄H₉ = C₈H₁₈