Amount of Substance (Moles)

The mole is the chemist's counting unit: one mole contains the Avogadro constant $6.02\times10^{23}$ particles.

Key relationships

$$n = \frac{m}{M_r}, \quad n = c \times V, \quad n = \frac{V}{24}\,(\text{gas, dm}^3\text{ at rtp})$$ where $n$ = moles, $m$ = mass (g), $M_r$ = molar mass, $c$ = concentration (mol dm⁻³), $V$ = volume (dm³). For gases at rtp, one mole occupies 24 dm³. The ideal gas equation is $pV = nRT$ ($R = 8.31$).