Lab / Solutions
Molarity Calculator (Mass, Volume, Concentration)
Find how much to weigh out to make a solution of a given molarity and volume, or the molarity or volume from the mass, using the solute's molar mass, with units from molar to nanomolar.
Molarity Calculator (Mass, Volume, Concentration): Moles = mass ÷ molar mass and molarity = moles ÷ litres, so mass = molarity × volume × molar mass. 250 mL of 0.1 M sodium chloride, at 58.44 g/mol, needs 0.1 × 0.25 × 58.44 = 1.461 g. Rearranged, 5.844 g in 500 mL is 0.2 M. Runs 100% locally in your browser with zero server file uploads.
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Molarity is moles of solute per litre of solution, and moles are mass ÷ molar mass, so mass = molarity × volume × molar mass. For 250 mL of 0.1 M sodium chloride (58.44 g/mol), weigh 0.1 × 0.25 × 58.44 = 1.461 g, dissolve it, and make it up to 250 mL. Use the molar mass of the exact form you weigh, including any water of crystallisation.
Worked examples
1 L of 1 M glucose (180.16 g/mol) needs 180.16 g. 100 mL of 50 mM Tris base (121.14 g/mol) needs 0.6057 g.
To find the molar mass from a formula, use the molar mass calculator.
From stock to working solution
It is usually easier to make a concentrated stock and dilute it than to weigh tiny masses: 10 mL of a 100 mM stock needs ten times the mass of a 10 mM one.
The dilution calculator works out the volume of stock for each working solution.
How to use it
- Enter the solute's molar mass in g/mol.
- Choose what to work out: mass, molarity, or volume.
- Enter the other two, and read the answer.
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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.
Where do I get the molar mass?
From the label, or work it out from the formula with the molar mass calculator; use the formula of the form you weigh, such as CuSO₄·5H₂O.
How do I make the solution?
Dissolve the solute in less than the final volume, then make it up to the mark in a volumetric flask; adding the solute to the full volume gives a slightly lower concentration.
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