The combustion of 135.0 mg of a hydrocarbon produces 440.0 mg of CO2 and 135.0 mg of H2 O . The

The combustion of 135.0 mg of a hydrocarbon produces 440.0...

The combustion of 135.0 mg of a hydrocarbon produces $440.0 \mathrm{mg}$ of $\mathrm{CO}_{2}$ and $135.0 \mathrm{mg}$ of $\mathrm{H}_{2} \mathrm{O} .$ The molar mass of the hydrocarbon is $270 \mathrm{g} / \mathrm{mol}$. Determine the empirical and molecular formulas of this compound.

Key Concepts

Combustion Analysis

Combustion analysis is a technique used to determine the elemental composition of a compound, typically by burning the compound and analyzing the resulting products. In organic chemistry, this involves measuring the amounts of CO? and H?O produced from the complete combustion of a hydrocarbon to deduce the quantities of carbon and hydrogen present in the original sample.

Empirical Formula Determination

The empirical formula represents the simplest whole-number ratio of the elements in a compound. In combustion analysis, the masses of CO? and H?O are used to calculate the moles of carbon and hydrogen, respectively. These mole calculations are then used to determine the simplest ratio of atoms in the compound.

Molecular Formula Determination

After obtaining the empirical formula, the molecular formula is determined by using the compound's molar mass. The molecular formula has the same elemental ratio as the empirical formula but in a multiple that corresponds to the actual molar mass, providing the true number of atoms of each element in a molecule.

Molar Mass

Molar mass is the mass of one mole of a substance and is crucial in converting between the mass of a sample and the number of moles. In the context of molecular formula determination, the empirical formula mass is compared with the given molar mass to establish the factor by which the empirical formula must be multiplied to obtain the molecular formula.

Stoichiometry in Combustion Reactions

Stoichiometry involves the quantitative relationships between reactants and products in a chemical reaction. In combustion analysis, the stoichiometric relationships between the hydrocarbon and the products (CO? and H?O) allow calculation of the number of moles of carbon and hydrogen present in the original compound based on the measured masses of the combustion products.