Determine the empirical and molecular formulas of each of the following substances: (a) Styrene, a compound used to make Styrofoam® cups and insulation, contains 92.3% C and 7.7% H by mass and has a molar mass of 104 g/mol.

Key Concepts

Empirical Formula

The empirical formula represents the simplest whole-number ratio of the elements in a compound. To determine it, the mass percentages of each element are converted to moles, and then the mole ratios are simplified to the smallest integers. For styrene, this involves calculating the moles of carbon and hydrogen based on their mass percentages.

Molecular Formula

The molecular formula indicates the actual number of atoms of each element in a molecule of the compound. It can be derived from the empirical formula by comparing the molar mass of the compound to the molar mass of the empirical formula. In the case of styrene, knowing the molar mass (104 g/mol) allows for the determination of how many times the empirical formula fits into the molecular formula.

Molar Mass

Molar mass is the mass of one mole of a substance, typically expressed in grams per mole (g/mol). It is calculated by summing the atomic masses of all atoms in a molecular formula. For styrene, the molar mass is crucial for determining the molecular formula from the empirical formula, as it provides the necessary information to scale the empirical formula to the actual molecular composition.