Chemistry: Finding empirical formula from moles

Question

Question: Combustion of an alkane produces 3 moles of water and 2 moles of carbon dioxide. What is its empirical formula?

Options:

1. C2H3
2. CH2
3. CH3
4. CH

(Ans: CH3)

Answer 1

Find moles of C and moles of H

moles of C: 2 moles CO₂ x 1 mol C / mol CO₂ = 2 mols C

moles H: 3 moles H₂O x 2 mol H / mol H₂O = 6 mols H

Ratio is 2 C : 6 H which reduces to 1C : 3 H

Emirical formula = CH₃