What is the mass percent (m/m) of a solution containing 55 grams of calcium chloride, CaCl2, and 125 grams of water? 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 m solvent: Molality = nsolute / m solvent = msolute / (W solute * m solvent) where
The molality unit from 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 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:
Now the #"moles of solute"# are a constant. The volume of solution MAY change substantially with increasing or decreasing temperature. In some calculations #"molality"# is used in preference, which is defined by the quotient.... #"molality"="moles of solute"/"kilograms of solvent"# ....this is temperature independent, and at lower concentrations, #"molarity"-="molality"#.
To get the molarity, you divide the moles of solute by the litres of solution. #"Molarity" = "moles of solute"/"litres of solution"# For example, a 0.25 mol/L NaOH solution contains 0.25 mol of sodium hydroxide in every litre of solution. To calculate the molarity of a solution, you need to know the number of moles of solute and the total volume of the solution. To calculate molarity:
EXAMPLE: What is the molarity of a solution prepared by dissolving 15.0 g of NaOH in enough water to make a total of 225 mL of solution? Solution: 1 mol of NaOH has a mass of 40.00 g, so #"Moles of NaOH" = 15.0 cancel("g NaOH") × "1 mol NaOH"/(40.00 cancel("g NaOH")) = "0.375 mol NaOH"# #"Litres of solution" = 225 cancel("mL soln") × "1 L soln"/(1000 cancel("mL soln")) = "0.225 L soln"# #"Molarity" = "moles of solute"/"litres of solution" = "0.375 mol"/"0.225 L" = "1.67 mol/L"# Some students prefer to use a "molarity triangle".  It summarizes the molarity formulas as #"Moles" = "molarity × litres"# #"Molarity" = "moles"/"litres"# #"Litres" = "moles"/"molarity"#
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What is the molality of a solution prepared from 12.5 g kno3 and 75.0 g h2o?
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