Module 1: Moles, Molar Mass, Percent Composition & Empirical Formulae

Vocabulary flashcards covering core topics including Avogadro's number, moles, molar mass, percent composition, empirical formulas, molecular formulas, and chemical laws.

Mole

A collection that contains Avogadro's number ($N_A = 6.02214076 \times 10^{23}$) of items.

Avogadro's Number ($N_A$)

The number of items in one mole of a substance, defined as $6.02214076 \times 10^{23}$, which equals the number of atoms in $12\,g$ of carbon or $1\,g$ of hydrogen.

Molar Mass

The mass in grams of one mole of a substance (atoms or molecules), expressed in units of $g\,mol^{-1}$.

Formula Mass

The sum of the average atomic masses of all atoms represented in the chemical formula of a substance, representing the mass of one mole of that compound.

Percent Composition

The percentage by mass of each element contained within a compound, calculated as $\% \text{Element} = \frac{\text{mass of element}}{\text{molar mass}} \times 100$.

Law of Multiple Proportions

The principle stating that when two elements react to form more than one compound, a fixed mass of one element will react with masses of the other element in a ratio of small, whole numbers.

Empirical Formula

The chemical formula of a compound expressed in the lowest whole-number mole ratio of its constituent atoms.

Molecular Formula

A chemical formula that specifies the actual number of atoms of each element present in a molecule, which is an integer multiple of the empirical formula.

Mohr's Salt

A hydrated salt with the molecular formula $(NH_4)_2Fe(SO_4)_2 \cdot 6H_2O$ (ammonium iron(II) sulfate hexahydrate), having a calculated formula mass of $392.137\,g\,mol^{-1}$.

Empirical Formula Decimal Multipliers

Integer factors used to multiply decimal mole ratios to convert them to whole numbers when calculating an empirical formula (e.g., multiply $1.5$ by $2$; $1.33$ or $1.67$ by $3$; $1.25$ or $1.75$ by $4$).