How this calculator works
Divide the solute amount by kilograms of solvent. The denominator excludes solute mass. Mass mode converts the weighed solute using its molar mass. Unlike molarity, molality does not directly change when the solution expands with temperature, provided composition remains unchanged.
Formula
b = n_solute / m_solvent(kg).
Worked example
0.5 mol in 1 kg solvent is 0.5 mol/kg. A 20 g solute with M = 100 g/mol in 0.4 kg solvent also gives 0.5 mol/kg.
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Frequently asked questions
Can I use solution mass?
Subtract solute mass first; molality uses only the solvent mass.
Does the solvent need to be water?
No. The definition applies to any stated solvent.
Which units define molality?
Molality is moles of solute per kilogram of solvent. Use the solvent mass selector for grams or other mass units.