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Molality Calculator

Calculate molality from the amount of solute and the mass of solvent.

What do you know?

Enter the mass of the solute.

If a valid formula is entered, its molar mass is calculated automatically.

Molar mass: 58.44 g/mol

Molar mass

Enter the mass of the solvent only, not the total solution.

Important: Use the solvent's mass, not the total solution mass.

Molality

1.711 mol/kg

1.711 m

Moles of solute
0.1711 mol
Solvent mass
0.1 kg
Molar mass
58.44 g/mol

Try an example:

Calculation working

How it was calculated

  1. 1. Moles of solute

    10.0 g ÷ 58.44 g/mol = 0.1711 mol

  2. 2. Solvent mass

    100.0 g ÷ 1000 = 0.1 kg

  3. 3. Molality

    0.1711 mol ÷ 0.1 kg = 1.711 mol/kg

What is molality?

Molality tells you how many moles of solute are present for each kilogram of solvent.

m = moles of solute ÷ kilograms of solvent

Molality vs molarity

Molality

Moles of solute ÷ kg of solvent

Molarity

Moles of solute ÷ L of solution

The key difference is what goes in the denominator: molality uses solvent mass, while molarity uses the final solution volume.

How it works

Four short steps

  1. Find the moles of solute

    Use the number of moles directly, or calculate moles from solute mass and molar mass.

  2. Find the solvent mass

    Use the solvent only, not the total solution.

  3. Convert the solvent mass to kilograms

    Convert grams to kilograms if necessary.

  4. Divide moles by kilograms

    Moles of solute ÷ kg of solvent gives molality.

Use the solvent, not the solution

Don't use the mass of the entire solution. Molality uses the mass of the solvent only.

Don't confuse molality (mol/kg) with molarity (mol/L).

Why molality is used

Molality is based on mass rather than volume, so it does not change just because temperature changes the volume of a solution. This makes it especially useful in calculations involving boiling-point elevation and freezing-point depression.

Keep going

Related tools

Need the number of moles first?

Moles Calculator

Need the molar mass?

Molar Mass Calculator

Working with solution concentration?

Molarity Calculator

Need to change a solution's concentration?

Dilution Calculator

FAQ

Frequently asked questions

What is molality?

Moles of solute per kilogram of solvent.

What is the formula for molality?

m = moles of solute ÷ kilograms of solvent.

What is the difference between molality and molarity?

Molality uses kilograms of solvent. Molarity uses liters of solution.

Do I use the mass of the solvent or the solution?

Use the mass of the solvent only. Do not include the dissolved solute in the denominator.

Can I enter solvent mass in grams?

Yes. The calculator converts grams to kilograms automatically.

Can I calculate molality from solute mass?

Yes. You need the solute's molar mass to convert its mass to moles.

Does temperature affect molality?

Molality is based on mass rather than volume, so temperature-related volume changes do not directly change the molality.

What unit is molality measured in?

The standard unit is mol/kg, also commonly written as m (molal).