Molality Calculator
Per kilogram of solvent — not per litre of solution.
Work out Molality. Per kilogram of solvent — not per litre of solution. Free, with no account and nothing to download.
Molality (mol/kg)
4
2 mol in 0.5 kg of solvent
Molality is per kilogram of solvent; molarity is per litre of solution. The distinction matters whenever temperature changes: volume expands with heat and mass does not, so a solution's molarity drifts as it warms while its molality is fixed. That is why colligative property calculations — boiling point, freezing point, osmotic pressure — are all defined on molality.
How the Molality Calculator works
Molality is moles per kilogram of solvent; molarity is moles per litre of solution. The distinction matters whenever temperature changes, because volume expands with heat and mass does not — which is why every colligative property is defined on molality.
Also known as: molality vs molarity · moles per kilogram calculator · molal concentration calculator · how to calculate molality
Frequently asked questions
What is the difference between molality and molarity?
Molality is per kilogram of solvent, molarity per litre of solution. Molality is temperature-independent because mass does not expand; molarity drifts as a solution warms.
How do I calculate molality?
Divide moles of solute by kilograms of solvent. Two moles in 500 g of water is 4 molal.
Why do freezing point calculations use molality?
Because they are performed across a temperature range by definition, and a concentration that changes with temperature would make the equation circular.
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