Molarity Calculator

Molarity (M) is moles of solute per liter of solution: M = n ÷ V. First find moles: n = mass ÷ molar mass. Volume must be in liters for molarity in mol/L.

Molarity changes with temperature because liquid volume expands. For precise lab work, molality (moles per kg solvent) is sometimes preferred. This calculator assumes volume in liters at your stated conditions.

Example: 58.44 g of NaCl (molar mass 58.44 g/mol) dissolved in 1 L is exactly 1.0 M NaCl — one mole in one liter.

Dilution problems use M₁V₁ = M₂V₂ when you add solvent without changing moles of solute. This calculator finds initial molarity from mass and volume — use the dilution formula separately when topping up a flask.

Always distinguish solute mass from solution volume. Dissolving 58.44 g NaCl and bringing the flask to 1 L total volume is 1.0 M; dissolving in exactly 1 L of water before expansion gives a slightly different final concentration.

Worked example with defaults: 58.44 g solute, molar mass 58.44 g/mol, 1 L volume → 1.0000 mol ÷ 1 L = 1.0 M. Doubling mass to 116.88 g in the same volume doubles molarity to 2.0 M.

Stock solutions simplify lab prep: a 10× buffer made at 10 M diluted 1:10 gives 1 M working strength via M₁V₁ = M₂V₂. This calculator finds the molarity you started with from mass, molar mass, and final volume — the first step before any dilution math. Label volumetric flasks at the meniscus after dissolution — the initial water volume before q.s. to mark differs from the final liter used in M = n/V.

For acids like H₂SO₄ that donate two protons, normality can differ from molarity even when mass and volume match. Molarity counts moles of solute per liter; normality counts reactive equivalents — check your titration protocol before substituting one for the other. Same mass and volume can yield different normality for diprotic acids — check whether your titration protocol expects equivalents or moles per liter.

Doubling volume from 1 L to 2 L while keeping 58.44 g NaCl halves molarity to 0.5 M because the same moles occupy twice the space. Halving mass at fixed 1 L volume has the same effect — moles and liters trade off linearly in M = n/V. Tripling mass to 116.88 g in 1 L without adding solvent yields 2.0 M, a useful check when scaling stock solutions in the lab.