Molarity Calculator
Enter any three of mass, molar mass, volume, and molarity to find the fourth.
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Common Molar Masses
| Compound | Formula | Molar Mass (g/mol) |
|---|---|---|
| Sodium chloride | NaCl | 58.44 |
| Sodium hydroxide | NaOH | 40.00 |
| Hydrochloric acid | HCl | 36.46 |
| Sulfuric acid | H₂SO₄ | 98.08 |
| Glucose | C₆H₁₂O₆ | 180.16 |
| Calcium chloride | CaCl₂ | 110.98 |
| Potassium permanganate | KMnO₄ | 158.03 |
How to Calculate Molarity
Molarity (M) is the number of moles of solute per liter of solution. It is the most common way to express concentration in chemistry.
To prepare a solution of known molarity: (1) calculate the mass needed using mass = M × V × molar mass, (2) weigh the solute, (3) dissolve in less than the final volume of solvent, (4) dilute to the final volume in a volumetric flask.
Molarity (M) = moles of solute / liters of solution. Moles = mass (g) / molar mass (g/mol). To prepare 500 mL of 0.1 M NaCl (molar mass 58.44 g/mol): moles needed = 0.1 × 0.5 = 0.05 mol. Mass = 0.05 × 58.44 = 2.92 g. Dissolve 2.92 g of NaCl in approximately 400 mL of deionized water, then add water to the 500 mL mark on a volumetric flask.
Always add solute to water (not water to solute) when preparing solutions, especially for strong acids and bases — the dissolution of concentrated sulfuric acid in water is violently exothermic. Add acid slowly to a water-filled container while stirring.
Molality (m) vs. molarity (M): molality = moles / kg of solvent (not solution). Molality doesn't change with temperature since mass is temperature-independent, making it preferred for boiling point elevation and freezing point depression calculations (colligative properties). For dilute aqueous solutions at room temperature, molarity ≈ molality numerically.
Normality (N) = molarity × equivalents per mole. For acid-base reactions, equivalents = number of H⁺ or OH⁻ ions. H₂SO₄ has 2 equivalents: 1 M H₂SO₄ = 2 N H₂SO₄. For redox reactions, equivalents = electrons transferred per mole. Normality is used in titration calculations and clinical chemistry.
See also: Dilution Calculator · pH Calculator