Percent Composition, Empirical & Molecular Formulas

Percent composition is the percentage by mass of each element in a compound, calculated by dividing the mass of each element by the total mass of the compound and multiplying by 100.

Percent by mass = (mass of element in 1 mole of compound / molar mass of compound) x 100.

The empirical formula is the simplest whole-number ratio of atoms of each element in a compound.

Convert the percent composition to grams, then to moles, and find the simplest ratio of moles of each element.

The molecular formula shows the actual number of atoms of each element in a molecule of a compound.

Multiply the subscripts in the empirical formula by a whole number (n) to match the molecular mass.

The molecular formula is a multiple of the empirical formula, representing the actual number of atoms in a molecule.

Percent by mass of F = (2 * 19.00 / (40.08 + 2 * 19.00)) * 100 = 49%.

The empirical formula is CH2.

Percent by mass of Na = (22.99 / (22.99 + 35.45)) * 100 = 39%.