Molarity vs Molality: What's the Difference?
Two concentration units, one letter apart, both pronounced almost identically. The difference comes down to a single word in each definition — solution versus solvent — and that one word changes when you'd use each. The short answer: molarity (M) is moles of solute per litre of solution . Molality (m) is moles of solute per kilogram of solvent . Molarity measures the final mixture by volume; molality measures only the solvent, by mass. Quick comparison at a glance Feature Molarity (M) Molality (m) Definition mol solute ÷ L of solution mol solute ÷ kg of solvent Units mol/L mol/kg Denominator measures The whole mixture Only the solvent Measured by Volume Mass Changes with temperature? Yes — liquids expand No — mass is fixed Best used for Titrations, everyday lab work Boiling point and freezing point problems How you prepare it Dissolve, then top up to the mark Weigh solute and solvent separately What is molarity? Molarity is the concentration unit you'll use...