Answer to Question #152491 in General Chemistry for Dimple Callangan

Question

Octane contains only C and H. Combustion of 30g of octane produced 92.63 grams of CO2 and 42.63 grams H2O. The molar mass of octane is 114g. Calculate the empirical formula and molecular formula of octane.

Answer 1

Any alkane on combustion will lead to CO₂ and H₂O formation.

No. of moles of CO₂ formed = 92.63/44 = 2.10 moles

No. of moles of H₂O formed = 42.63/18 = 2.36 moles

Moles of octane taken = 30/114 = 0.263 moles

so on taking ration of moles we get for 1 mole of octane we get 8 moles of carbon dioxide and

9 moles of water.

so total number of carbon in octane is 8 and hydrogen is 18.

Molecular formula is C₈H₁₈ and empirical formula is C₄H₉