Molality Calculator

Molality is one of the core ways chemists measure how concentrated a solution is, and this calculator works it out for you in a single step. Molality is the number of moles of dissolved substance, the solute, for each kilogram of the liquid it is dissolved in, the solvent. It is written with a lower-case m, and its great advantage over the more familiar molarity is that it is based on mass rather than volume, so it does not change when the temperature changes and the solution expands or contracts. That makes molality the right measure for the so-called colligative properties, the effects a dissolved substance has on boiling point, freezing point and vapour pressure, which is why it shows up whenever you study antifreeze, salting icy roads, or why seawater boils a little hotter than fresh water. To use the calculator, enter the mass of solute, its molar mass, and the mass of solvent in kilograms. It first converts the solute mass into moles by dividing by the molar mass, then divides those moles by the kilograms of solvent to give the molality, and it shows the moles of solute along the way so you can follow the working. It handles any solute as long as you know its molar mass, which you can read off the periodic table or a label, so it works equally well for salt, sugar, ethylene glycol or a reagent in the lab. Whether you are a chemistry student preparing solutions, checking homework, or working through colligative property problems, it removes the small arithmetic steps where errors creep in. The formula and a worked example are explained clearly below.

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