Molality Calculator
The molal concentration: moles of solute per kilogram of solvent.
Result
Molality (mol/kg)
0.5000
How it works
Molality is concentration per kilogram of solvent: moles of solute divided by the solvent's mass, not the solution's volume. That single difference from molarity is what makes it useful. Because mass does not change with temperature while volume does, molality is constant whatever the thermometer says. A 1 m solution is 1 m at 0 °C and at 80 °C, whereas its molarity falls as the liquid warms and expands. Precise physical chemistry therefore prefers molality. It is also the concentration that appears in the colligative properties — the laws governing how a dissolved substance shifts a solvent's freezing and boiling points. Those laws are written in molality precisely because they must hold across a temperature range, which a volume-based measure cannot do.
Advertisement
Frequently asked questions
Why use molality?
It is temperature-independent, useful for boiling-point and freezing-point calculations.
Molality vs molarity?
Molality uses kilograms of solvent; molarity uses litres of solution.
Why does salt melt ice?
Dissolved salt lowers water's freezing point, and the shift is proportional to molality — roughly 1.86 °C per mole of particles per kilogram. Enough salt keeps water liquid several degrees below zero, which is exactly why it is spread on roads.
Advertisement