Chemistry / Unit 8 Chem 1547 short lesson, about 20 seconds
Mole Fraction and Molality
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The idea
Mole fraction is a component's moles divided by total moles present; molality is solute moles divided by kilograms of solvent, temperature-independent.
In practice
A solution's molarity shifts slightly as temperature changes its volume, but that same solution's molality stays fixed instead.
Where people slip
Molality divides by the mass of solvent alone, not the whole solution — confusing the two gives a close but wrong value.
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