Question

A compound containing only C, H, and O, was extracted from the bark of the sassafras tree. The combustion of 40.1 mg produced 109 mg of CO2 and 22.3 mg of H2O. The molar mass of the compound was 162 g/mol. Determine its empirical and molecular formulas.

Answer 1

Moles of CO2 = mass/molecular weight

= 109 mg / 44g/mol

= 2.477 mol = moles of C

Mass of C = moles x molecular weight

= 2.477 mol x 12 g/mol

= 29.727 g

Moles of H2O = 22.3/18 = 1.2388 mol

Moles of H = 2*1.2388 = 2.4776 mol

Mass of H = 2.4776 mol x 1 g/mol = 2.4776 g

Mass of O = total mass - mass of C - mass of H

= 40.1 - 29.727 - 2.4776

= 7.8954 g

Moles of O = 7.8954/16 = 0.4934 mol

Molar ratio

C : H : O = 5 : 5 : 1

Empirical formula = C5H5O

Molar mass of Empirical formula = 81

Molar mass of molecular formula = 162

Multiplying factor = 162/81 = 2

Molecular formula = (C5H5O)2 = C10H10O2