Amount of Substance Practice Flashcards

Vocabulary flashcards covering relative atomic/molecular masses, the mole, ideal gas laws, formulae calculations, stoichiometry, and atom economy.

Relative atomic mass ($A_r$)

The weighted average mass of an atom of an element, taking into account its naturally occurring isotopes, relative to the relative atomic mass of an atom of carbon-12.

Relative molecular mass ($M_r$)

The mass of a molecule compared to the relative atomic mass of an atom of carbon-12, calculated by adding up the relative atomic masses of all the atoms present in the molecule.

Relative formula mass

The term used for the relative mass of ionic compounds because they do not exist as molecules, though it uses the same symbol ($M_r$).

Avogadro constant

The number of atoms in exactly $12\,g$ of carbon-12, which is approximately $6.022 \times 10^{23}$.

Mole

The amount of substance that contains $6.022 \times 10^{23}$ particles (entities).

Entity

A general word for a particle, which can refer to an atom, molecule, ion, electron, or the simplest formula unit of a giant ionic structure.

Molar mass

The mass per mole of a substance, which has units of $kg\,mol^{-1}$ or $g\,mol^{-1}$.

Solution

A mixture consisting of a solvent with a solute dissolved in it.

Concentration

A measurement of how much solute is present in a known volume of solution, typically measured in $mol\,dm^{-3}$.

Boyle's law

The principle stating that the product of pressure and volume is a constant, provided the temperature remains constant: $P \times V = \text{constant}$.

Charles' law

The principle stating that volume is proportional to temperature, provided the pressure remains constant: $\frac{V}{T} = \text{constant}$.

Gay-Lussac's law

Also called the constant volume law; it states that pressure is proportional to temperature, provided the volume remains constant: $\frac{P}{T} = \text{constant}$.

Ideal gas equation

The equation linking pressure, volume, number of moles, the gas constant, and temperature: $PV = nRT$.

Gas constant ($R$)

The constant used in the ideal gas equation with a value of $8.31\,J\,K^{-1}\,mol^{-1}$.

Standard SI units for $PV = nRT$

The required units for the ideal gas equation where pressure ($P$) is in $Pa$, volume ($V$) is in $m^3$, and temperature ($T$) is in $K$.

Empirical formula

The formula that represents the simplest whole number ratio of the atoms of each element present in a compound.

Molecular formula

The formula giving the actual number of atoms of each element in one molecule of a compound.

Combustion analysis

A method used to find empirical formulae of organic compounds by burning them in excess oxygen and measuring the resulting water, carbon dioxide, and other oxides.

Stoichiometry

The ratio in which reactants react and products are produced in a chemical reaction, expressed in simple whole numbers.

State symbols

Letters in brackets added to formulae in equations to indicate the physical state: $(s)$ for solid, $(l)$ for liquid, $(g)$ for gas, and $(aq)$ for aqueous solution.

Spectator ions

Ions that appear on both sides of a chemical equation but do not take part in the overall reaction.

Titration

An experimental technique used to find the concentration of a solution by reacting it with another solution of known concentration.

Atom economy

A theoretical measure of the efficiency of a reaction, calculated as $\frac{\text{mass of desired product}}{\text{total mass of reactants}} \times 100$.

Percentage yield

A measure of the practical efficiency of a process, calculated as $\frac{\text{actual number of moles of product}}{\text{theoretical maximum number of moles}} \times 100$.