A 0.125 g sample of unknown hydrocarbon is prepared for combustion analysis. After the hydrocarbon undergoes complete combustion, 0.4225 g of CO2 and 0.0865 g of H2O are produced. What is the empirical formula of the unknown

Empirical formula is CH

Explanation:

A hydrocarbon, CₐHₓ reacts with oxygen in the combustion reaction as follows:

CₐHₓ + O₂ → a CO₂ + x/2 H₂O

That means we can find the moles of C and H from the moles of CO2 and H2O. As empirical formula is defined as the simplest whole-number ratio of atoms in a molecule, we can determine it as follows:

Moles CO2 = Moles C -Molar mass: 44.01g/mol:

0.4225g * (1mol / 44.01g) = 0.0096 moles C

Moles H2O -Molar mass: 18.01g/mol:

0.0865g H2O * (1mol / 18.01g) = 0.0048moles H2O * (2mol H / 1mol H2O) =

0.0096 moles H

The ratio of atoms of C:H is:

0.0096moles C / 0.0096moles H = 1

That means empirical formula is CH