Chemistry
Calculate molar concentration (molarity) from mass or moles and solution volume.
Molarity
1.00 mol/L
1.0000 mol in 1 L
Molarity (M) is moles of solute per litre of solution. Formula: M = moles ÷ volume (L). To find moles from mass, divide mass (g) by molar mass (g/mol).
Molarity (M) is a measure of solution concentration defined as the number of moles of solute per litre of solution. It's one of the most common ways to express concentration in chemistry because it directly relates to the number of particles and allows chemists to predict reaction outcomes based on stoichiometry. A 1 M solution contains 1 mole of solute in enough solvent to make 1 litre of total solution.
The calculator uses two approaches. From mass: it divides the mass of solute (in grams) by its molar mass to find moles, then divides moles by solution volume. From moles: it directly divides the number of moles by solution volume in litres. Both give molarity in mol/L.
M = moles ÷ volume (L)
OR
M = (mass in g ÷ molar mass in g/mol) ÷ volume (L)Molarity divides the amount of solute (as moles) by the total volume of the solution in litres. To convert from mass to moles, divide the mass of your solute by its molar mass (the mass of one mole). The solution volume must include both the solute and solvent (i.e., the final volume after dissolution).
| Input | Result | Notes |
|---|---|---|
| Dissolve 58.44 g of NaCl (molar mass 58.44 g/mol) in water to make 1 L of solution | Molarity = 1 M | This is a standard 1 M salt solution, commonly used in labs |
| 2 moles of glucose in 500 mL of water | Molarity = 4 M (2 mol ÷ 0.5 L) | A 4 M glucose solution; concentrated enough for enzyme assays |
| 10 g of CaCl₂ (molar mass 110.98 g/mol) in 200 mL of solution | Molarity ≈ 0.45 M (0.09 mol ÷ 0.2 L) | Useful for calcium supplementation or electrolyte solutions |
Molarity is moles per litre of solution (volume-based); molality is moles per kilogram of solvent (mass-based). Molarity is more common in labs because solutions are measured by volume. Molality is used for colligative properties (boiling point, freezing point) and when temperature changes significantly.
When you dissolve a solid, its volume contributes to the total. For example, dissolving 58.44 g of NaCl in 1 L of water gives slightly more than 1 L of solution. Precise work requires a volumetric flask to measure the final volume after complete dissolution.
Use the dilution formula M₁V₁ = M₂V₂: multiply starting molarity by starting volume, then divide by your target volume. For example, to dilute 1 M HCl to 0.1 M, use 100 mL of stock and add water to reach 1 L total.
Theoretically, molarity can be any positive value. But in practice, solutions under 0.001 M (1 millimolar) become difficult to prepare accurately because you're dissolving tiny masses. For extreme dilutions, use stepwise serial dilutions.
Yes. As temperature increases, solutions expand slightly, lowering molarity. Most lab solutions assume 20–25 °C. For precise work (especially with concentrated acids), measure volume at the temperature you'll use the solution.
Normality (N) is moles of reactive particles (equivalents) per litre; it's used for acids and bases. For HCl, 1 M = 1 N (one acidic proton). For H₂SO₄, 1 M = 2 N (two protons). Molarity is now preferred in most fields.