Paradichlorobenzene, a common ingredient in solid air...

Paradichlorobenzene, a common ingredient in solid air fresheners, contains only $\mathrm{C}, \mathrm{H},$ and $\mathrm{Cl}$ and has a molar mass of about $147 \mathrm{g}$. Given that combustion of $1.68 \mathrm{g}$ of this compound produces $3.02 \mathrm{g} \mathrm{CO}_{2}$ and $0.412 \mathrm{g} \mathrm{H}_{2} \mathrm{O}$, determine its empirical and molecular formulas.

Key Concepts

Combustion Analysis

Combustion analysis is a technique used to determine the elemental composition of a compound by burning a known quantity of the substance and measuring the amounts of the combustion products. This method typically involves converting carbon into carbon dioxide and hydrogen into water, allowing for the quantification of these elements in the original compound.

Empirical Formula Determination

The empirical formula represents the simplest whole-number ratio of the elements in a compound. In combustion analysis, the masses or moles of carbon and hydrogen can be calculated from the amounts of CO2 and H2O produced, and when combined with any other elemental information (such as chlorine content in some compounds), the simplest ratio among the elements is determined.

Molecular Formula Determination

The molecular formula of a compound provides the actual number of atoms of each element in a molecule. Once the empirical formula is found, the molecular formula can be determined by comparing the empirical formula mass to the compound’s experimentally determined molar mass, thus revealing the multiple that must be applied to the empirical formula.

Stoichiometry

Stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It underpins the conversion of measured masses in combustion products to moles of constituent elements, facilitating the calculation of the empirical and molecular formulas.

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