Molarity Calculator
Find the molarity of a solution, the grams of solute to weigh out, the final volume of the solution, or how to dilute a stock solution with C1V1 = C2V2.
This molarity calculator divides moles of solute by liters of solution. To make 250 mL of 5.30 M sodium chloride, multiply 5.30 by 0.250 L to get 1.325 mol, then by the molar mass, 58.44 g/mol, to get 77.43 g of salt. The calculator also solves for molarity, volume or a dilution.
This calculator is for coursework and routine lab preparation and is not a substitute for a written lab procedure. It assumes the molar mass you enter is right and the solute dissolves fully, and it does not correct for purity, for salts that hold water in their crystals, or for temperature.
Mass of solute needed
77.43 g
- Moles of solute
- 1.325 mol
- Molarity
- 5.3 M
- Mass
- 77.43 g
- Volume
- 250 mL
Shown to 4 significant figures. Make the solution up to the final volume; do not just add the solute to that much water.
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About the Molarity Calculator
Molarity, written M, counts how many moles of a substance are dissolved in each liter of the finished solution. Moles come from grams divided by the molar mass, which is the sum of the atomic masses in the formula; for sodium chloride that is 22.99 plus 35.45, or 58.44 g/mol. So the three quantities link in one line: moles = molarity x liters = grams / molar mass. The textbook example credited below uses the same numbers, 1.325 mol and 77.4 g of salt in 0.250 L of 5.30 M solution; the calculator shows 77.43 g, to four significant figures, using 58.44 g/mol. Volume always means the final volume of solution, so dissolve the solid in less water and then fill the flask to the final-volume line. For a dilution, the moles stay the same, which gives C1V1 = C2V2: taking 25 mL of 5.30 M stock to 1.00 M needs a final volume of 132.5 mL, which is about 107.5 mL of added water; for accuracy, put the stock in a flask and fill to 132.5 mL rather than measuring the water separately.
Frequently asked questions
How do I calculate molarity?+
Divide the grams of solute by its molar mass to get moles, then divide by the liters of solution. 10 g of sodium chloride in 0.5 L is 10 / 58.44 / 0.5, about 0.342 M.
How many grams do I need for a solution?+
Multiply the molarity by the volume in liters to get moles, then by the molar mass. For 250 mL of 0.200 M calcium chloride at 110.98 g/mol, that is 0.200 x 0.250 x 110.98, or 5.55 g.
How does C1V1 = C2V2 work?+
Diluting adds solvent but not solute, so the moles before and after are equal. Concentration times volume is moles, which gives C1V1 = C2V2. Solve for the final volume, then subtract the stock volume to find about how much solvent to add; filling to the final volume is more exact, because volumes do not always add up exactly when liquids mix.
Is molarity the same as molality?+
No. Molarity divides by liters of solution, which changes slightly with temperature. Molality divides by kilograms of solvent. This calculator works in molarity only.
Definitions, and the sodium chloride numbers in: OpenStax, Chemistry 2e (2019), section 3.3, Molarity: M = mol solute / L solution, the dilution equation C1V1 = C2V2, and Example 3.17 (77.4 g of NaCl in 0.250 L of 5.30 M solution).
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