Molality is expressed as moles solute/kg solvent. Moles of solute = 2. Kg solvent = 6.Molality = 2 moles/6 kg = 0.33 molal With this molality calculator you can quickly calculate the molality - one way of measuring the concentration of a solute in a solution (not to be confused with molarity). Simply type the number of moles of your solute substance and mass of the solvent and the tool will calculate the molality. If you don't know how many moles of a substrate you have, use the advanced mode to calculate it with the use of mass and molar mass of the compound. Are you still unsure what's the molality definition, its units and formula - or simply how to calculate molality step by step? Keep reading and you'll find the answer!
Molality, also called molal concentration, is defined as the amount of substance of solute, divided by the mass of the solvent msolvent: Molality = nsolute / msolvent = msolute / (Wsolute × msolvent) where
The molality unit from the SI system is mol/kg; sometimes, the name molal is used (though it's considered obsolete). Molality plays a significant role in calculating the ionic strength of a solution.
Molarity and molality are similar concepts - both are measures of the concentration of a solution. However, there is one main difference between those terms: molarity is expressed as the amount of substance per unit volume of solution, whereas molality defines the concentration as the amount of substance per unit mass of the solvent.
We've put all the most important differences between those two terms into a short molarity vs. molality table:
To change between molarity and molality, you can use the following relation: M = m × d / (1 + m × W) where
Let's show on the example how to calculate molality:
To compute the molality of a solute, you need to:
The answer is 6 mol/kg. To see how this result is derived, recall that the formula for molality reads molality = moles of solute / mass of solvent in kg. Plugging in moles of solute = 3 and mass of solvent = 0.5 kg, we obtain molality = 3 / 0.5 = 6 mol/kg, as claimed.
The formula that allows us to convert molarity to molality is the following: m = M/( d - M × W) where:
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