S1.4 Counting particles by mass: the mole

Mole (mol)

The SI unit for amount of substance; one mole contains exactly 6.02×10²³ particles (Avogadro's constant)

Avogadro's constant (NA)

6.02×10²³ mol⁻¹ — the number of particles (atoms, molecules, ions) in one mole of a substance

Molar mass (M)

The mass of one mole of a substance, in g mol⁻¹, numerically equal to the relative atomic/molecular/formula mass

Empirical formula

The simplest whole-number ratio of atoms of each element in a compound

Molecular formula

The actual number of atoms of each element in a molecule of the compound; a whole-number multiple of the empirical formula

Molar volume of a gas

At STP (0°C, 100 kPa), one mole of any ideal gas occupies 22.7 dm³ (22 700 cm³)

Avogadro's law

Equal volumes of all gases, measured at the same temperature and pressure, contain equal numbers of molecules

Concentration

The amount of solute, in moles, dissolved per dm³ of solution (mol dm⁻³)

Limiting reagent

The reactant that is completely used up first in a reaction, and therefore determines the maximum amount of product that can form

Excess reagent

The reactant that remains left over once the limiting reagent has been fully consumed

Theoretical yield

The maximum amount of product that could be formed from a given amount of limiting reagent, calculated from the balanced equation

Percentage yield

(actual yield ÷ theoretical yield) × 100

Atom economy (HL)

(molar mass of desired product ÷ sum of molar masses of all reactants) × 100 — a measure of how much of the reactant mass ends up as useful product

Ideal gas equation (HL)

PV = nRT, where P = pressure (Pa), V = volume (m³), n = moles, R = 8.31 J K⁻¹ mol⁻¹, T = temperature (K)