Moles in a Formula

A formula counts moles too: 1 mol of H₂O holds 2 mol of H atoms and 1 mol of O atoms.

CaCl₂ is made of Ca²⁺ and Cl⁻ ions, two Cl⁻ for each Ca²⁺. One mole of it holds 1 mol of Ca²⁺ and 2 mol of Cl⁻: 3 mol of ions.

1 mol of CaCl₂: 1 mol of Ca²⁺ and 2 mol of Cl⁻

Multiply the moles of the substance by the particle's number in the formula: $0.5\ \mathrm{mol}$ of CaCl₂ holds $1\ \mathrm{mol}$ of Cl⁻.