Amount of Substance

A mole

The number of atoms in 12.00g of carbon-12.

Avogadro constant (L)

The number of atoms, molecules, ions or other entities in one mole (6.02 × 10²³).

Molar mass

The mass in grams of 1 mole of a substance (g mol⁻¹).

Relative molecular mass (Mr)

Sum of relative atomic masses of all atoms in a molecule compared to 1/12 mass of a carbon-12 atom.

Relative formula mass (Mr)

Sum of relative atomic masses of all atoms in an ionic formula compared to 1/12 mass of a carbon-12 atom.

Molar volume

The volume of 1 mole of a gas.

Molar concentration

The number of moles of a solute per litre of solution (mol dm⁻³).

Concentration

Amount per unit volume (usually mol dm⁻³ or g dm⁻³).

Stoichiometry

The ratio in which reactants react and products are produced, in whole numbers.

Law of conservation of mass

States that mass cannot be created or destroyed.

Limiting reactants

Reactants that restrict the amount of product that a reaction can produce.

Empirical formula

Shows the simplest ratio of atoms of each element present in a compound.

Molecular formula

Shows the actual number of atoms of each element present in one molecule of a compound.

Standard conditions

100kPa pressure and 298K temperature.

Titration

A technique used to find the concentration of an unknown solution by adding a known solution.

Endpoint of a titration

The point at which enough of the solution from the burette has been added to react completely.

Equivalence point

The point at which equal moles of acid and alkali are present.

Titre

The amount of solution added to reach the endpoint.

Acid

A substance which forms solutions with a pH < 7 and acts as a proton donor.

Base

A substance which acts as a proton acceptor for an acid.

Alkali

A base which dissolves in water to give a pH > 7.

Indicator

A weak acid that changes colour depending on whether it is in acid or alkaline conditions.

Strong acid/alkali

Dissociates or ionises fully in solution in water.

Weak acid/alkali

Dissociates or ionises partially in solution in water.

Standard solution

A solution of a known concentration.

Primary standard

A substance suitable for making a standard solution (high molar mass, high solubility, stable, not hygroscopic).

Yield

The amount of product you get from a reaction.

Atom economy

A measure of how many atoms in reactants end up in your desired product.

Measurement uncertainty

The potential error involved when using a piece of apparatus to make a measurement.

Percentage measurement uncertainty

Actual measurement uncertainty × 100% divided by the value recorded.