Practice Chemistry Test: The Mole and Formulas

Practice flashcards covering key definitions, molar masses, empirical and molecular formulas, percent composition, and gas conversions at STP from the chemistry test review.

Mole

A quantity representing $6.02 \times 10^{23}$ particles (atoms, molecules, or formula units) of a substance.

Molar Mass

The sum of the atomic masses of the elements in any chemical compound, expressed in grams per mole.

Molar Mass of $MgCl_2$

$95.21\,g$, calculated from the atomic mass of magnesium ($24\,g$) and two chlorine atoms ($35.5\,g \times 2$).

Molar Mass of $Ba(OH)_2$

$171\,g$, calculated from the atomic mass of barium ($137\,g$) plus two hydroxide groups ($34\,g$).

Empirical Formula

The lowest whole-number ratio of elements in a compound, determinable if either the individual element masses or percent composition is known.

Empirical Formula of $C_2Cl_6$

$CCl_3$, obtained by reducing the subscript ratio of carbon to chlorine to its simplest whole numbers.

Molecular Formula

A formula showing the actual number of atoms of each element in a molecule, such as $P_4O_{10}$ for an empirical formula of $P_2O_5$ with a molar mass of $283.88\,g$.

Molar Volume at STP

The volume occupied by one mole of any gas at standard temperature and pressure, equal to $22.4\,dm^3$ (or $22.4\,\text{liters}$).

Percent Composition of Water ($H_2O$)

$11\%\,H$ and $89\%\,O$ by mass.

Formula Mass of $Ba(NO_3)_2$

$261\,\text{amu}$, which is the sum of the atomic masses in the ionic compound barium nitrate.

Diatomic Molecule

A molecule consisting of two atoms bonded together, such as chlorine gas ($Cl_2$) in the BrINClHOF series.

Factors Affecting Gas Volume

Pressure, temperature, and number of molecules (gas volume does not depend on the chemical identity of the gas).

Number of Particles in 1 Mole

$6.02 \times 10^{23}$ particles, ensuring that equal molar amounts of different substances (e.g., $1\,\text{mole}$ of $O_2$ gas and $1\,\text{mole}$ of solid $Pb$) have the exact same number of particles.

Percent Metal in $Na_2O$

$74.19\%$, representing the mass percentage of sodium in sodium oxide.

Volume of $0.750\,\text{moles}$ of $CO_2$ at STP

$16.8\,\text{liters}$, calculated by multiplying $0.750\,\text{moles}$ by the conversion factor $22.4\,\text{liters/mole}$.

Mass of $33.6\,\text{liters}$ of $CO_2$ at STP

$66\,g$, calculated from $1.5\,\text{moles}$ of carbon dioxide gas at STP multiplied by its molar mass of $44\,g\,mol^{-1}$.