M = n / V = mass / (MW × V)
Molarity (M) is the most common concentration unit in chemistry: moles of solute per liter of solution. A 1 M solution contains 1 mole of solute dissolved in enough solvent to make 1 liter total. To prepare: weigh out the calculated mass (mass = M × V × MW), dissolve in less than the final volume of solvent, then add solvent to the volumetric mark. Molarity is temperature-dependent (volume changes with temperature). Common molarities: concentrated HCl ≈ 12 M, concentrated H₂SO₄ ≈ 18 M, concentrated NaOH ≈ 19 M. Dilute solutions use millimolar (mM = 10⁻³ M) or micromolar (μM = 10⁻⁶ M). Molarity is essential for stoichiometric calculations in titrations: moles = M × V(L).