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How do I find molar mass from molality?

Daniel Candler  Follow

In addition to the molality of the solution, which you might have determined using either boiling point elevation or freezing point depression, you will also need to know the composition of the solution in terms of mass of solute.

So, for example, from the mass of the solute and the mass of the solvent, you will be able to convert that concentration into grams solute / kg solvent.

When you divide that concentration by the molality of the solution (moles solute/kg solvent), you have:

(grams solute/kg solvent) / (moles solute/kg solvent) = grams solute/moles solute = molar mass

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Curtis Evans  Follow

molality = moles solute/kg solvent

Ms = mass of solvent in kg

m = mass of solute

MM = molar mass

molality = (m/MM)/Ms

MM = m/(Ms*molality)

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