Unit 1: Elemental Compositions of Pure Substances Flashcards

Vocabulary flashcards covering elemental composition of pure substances, mass percent, empirical formulas, and molecular formulas from AP Chemistry Topic 1.3.

Pure Substance

Matter that has a fixed composition and distinct properties, which can either be an element or a compound.

Law of Definite Proportion

A chemical law stating that the elemental composition of a substance is always the same, meaning the ratios of the masses of the constituent elements in any pure sample of that compound are always the same.

Formula Weight (FW)

The sum of the atomic weights for the atoms in a chemical formula.

Molecular Weight (MW)

The sum of the atomic weights for the atoms in a molecule.

Percent Composition

The percentage of the total mass of a compound that is due to a specific component, calculated as $\% \text{ composition} = \frac{\text{Mass due to specific component}}{\text{Total molar mass of compound}} \times 100$.

Empirical Formula

A chemical formula showing the simplest ratio of elements in a compound.

Molecular Formula

A chemical formula that represents the actual number of atoms in a molecule, determined by multiplying the subscripts of the empirical formula by the ratio of the molar mass to the empirical formula mass.