The term for concentration measured as moles of solute per litre of solution is molarity. It is calculated by dividing the amount of solute, in moles, by the solution’s total volume in litres: c = n/V. A 1-molar solution contains 1 mole of solute in each litre of finished solution.
Molarity is widely used in laboratory chemistry because solutions can be prepared to a precise final volume, often in a volumetric flask. The unit is mol/L, commonly written as M, although modern chemical nomenclature increasingly prefers “amount concentration” and units such as mol/L.
A common mix-up is molality. Molarity uses the volume of the entire solution, while molality measures moles of solute per kilogram of solvent. Because volume changes slightly with temperature, molarity can vary with temperature; molality is less affected. Density is mass per volume, and normality depends on chemical reaction capacity rather than simply moles per litre.
The idea also connects directly to Avogadro’s constant: one mole represents exactly 6.02214076 × 10^23 specified particles.