Chemistry

Molality Calculator

Enter solute mass, molar mass and solvent mass to get the molality.

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Your numbers

Your results

Molality (mol/kg)
Molality (mol/kg)
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Moles of solute
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Mass fraction of solute
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Molality Calculator by TheCalcTools

How the Molality Calculator works

Molality is moles of solute divided by kilograms of solvent (not solution). Because it uses masses, it does not change with temperature, which is why it is used for boiling-point and freezing-point calculations.

The formula

b = n_solute ÷ m_solvent (kg) = (mass ÷ molar mass) ÷ kg solvent

Worked example

Using the default values shown in the calculator:

Mass of solute (g)58.44
Molar mass of solute (g/mol)58.44
Mass of solvent1
  1. 58.44 g ÷ 58.44 g/mol = 1.00 mol of NaCl in 1 kg of water: 1.00 mol/kg.

Result:

Molality (mol/kg)1.0000
Moles of solute1.0000
Mass fraction of solute5.52%

Frequently asked questions

What is the difference between molality and molarity?

Molarity is moles per litre of solution; molality is moles per kilogram of solvent. For dilute aqueous solutions they are almost equal.

Sources and further reading

Molarity CalculatorFind molarity and moles from a mass of solute dissolved in a volume Boiling Point Elevation CalculatorEnter molality, the van 't Hoff factor and the solvent to get the boiling point… Freezing Point Depression CalculatorEnter molality, the van 't Hoff factor and the solvent to get the freezing point… Mole Fraction CalculatorEnter the moles of each component to get mole fractions Normality CalculatorConvert molarity to normality, or find normality from mass and volume Osmotic Pressure Calculator (π = iMRT)Enter molarity, the van 't Hoff factor and temperature to get osmotic pressure

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This calculator gives estimates for information only. Check important results independently before you rely on them. See our disclaimer.