Molar Concentration formula
| Symbol | Quantity | SI unit | Meaning |
|---|---|---|---|
| c | Molar concentration | mol/m³ | Molar concentration of the solution |
| m | Mass of solute | kg | Mass of solute dissolved |
| M | Molar mass of solute | kg/mol | Molar mass (formula weight) of the solute |
| V | Volume of solution | m³ | Final volume of the solution (not of the solvent) |
What is Molar Concentration?
Molar Concentration: Molarity is the amount of solute in moles per litre of solution.
Molarity (mol/L, written M) is the most common way to express concentration in the lab. To prepare a solution, weigh out m = c·M·V grams of solute, dissolve it, and make it up to the final volume in a volumetric flask.
Choose "Mass of solute" in the Calculate menu to answer "how many grams do I need?". Choose "Molar concentration" to find the molarity of a solution you have already made.
How to use this calculator
- Choose the quantity you want to find in the Calculate menu. It is highlighted as the result field.
- Enter the known values. Scientific notation such as
1.6e-11is accepted. - Select a unit for each value. Units are converted to SI automatically.
- The answer updates as you type. Open Show calculation steps to see the working, or use Copy result to share a link with your inputs.
Worked example
How concentrated is a solution of 5.844 g NaCl (M = 58.44 g/mol) made up to 100 mL?
- n = 5.844 / 58.44 = 0.100 mol.
- c = 0.100 mol / 0.100 L = 1.00 mol/L.
Frequently asked questions
What is the difference between molarity and molality?
Molarity is moles per litre of solution. Molality is moles per kilogram of solvent. Molality does not change with temperature, while molarity does slightly, because volume expands.
How do I account for a hydrate?
Use the molar mass of the hydrate you are weighing, e.g. CuSO₄·5H₂O = 249.69 g/mol, not anhydrous CuSO₄ = 159.61 g/mol.