15.1.1—Amount of substance is an SI base quantity with the base unit mol

Amount of substance n is measured in moles, allowing microscopic entities to be counted through a macroscopic quantity.

Name the entities being counted—atoms, molecules, ions or formula units—before converting between mass, moles and particles.

One mole of water means one mole of H₂O molecules, not one mole of hydrogen atoms alone.

Moles are not a mass unit; different substances have different masses per mole.