Worked example
Ten grams of a substance with a 58.44 g/mol molar mass is about 0.1711 mol. In 500 g of solvent, molality is about 0.3422 mol/kg.
Use solvent mass, not solution mass
The denominator is the mass of solvent before or within the prepared mixture, excluding the solute. NIST defines molality as amount of solute divided by solvent mass. If you only know total solution mass, you need the solute mass too before you can find solvent mass.
Molality and molarity differ
Molarity uses moles divided by final solution volume in liters. Molality uses moles divided by solvent kilograms. The two values cannot be exchanged merely by changing a prefix; composition and density would be needed. Use the molarity calculator when you have final solution volume.
Check the formula mass
The page accepts your molar mass in grams per mole. For a known chemical formula, the main grams-to-moles calculator can compute the formula mass first. Round the final answer to the precision supported by your measurements, not by the calculator display.
Explore the related calculation
For a different starting point, try the molarity calculator or return to the main calculator. Browse the complete tool directory for this site.
Reference and corrections
The definitions and assumptions above follow these sources; the examples and calculator arithmetic are original to this page.
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