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Binary Mixture Mole Fraction & Molality

Find solute mole fraction and mole percent in a two-component mixture, with optional molality from solvent molar mass.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

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Inputs and results stay in this browser tab. Bookify does not upload or store the values you enter.

Formula and method

One mole of solute plus four moles of solvent gives solute mole fraction 0.2, or 20 mol%. With solvent molar mass 100 g/mol, molality is 2.5 mol/kg.

Solute mole fraction = solute moles / total moles; molality = solute moles / solvent mass

Worked example

Enter these known values and leave the other values blank.

Moles of solute
1 mol
Moles of solvent
4 mol
Solvent molar mass
100 g/mol
Total moles in both components
5 mol
Solute mole fraction
0.2
Solute mole percent
20 %
Solute molality
2.5 mol/ kg

Assumptions and limitations

  • Both component amounts and solvent molar mass are positive. Pure-component endpoints are outside this two-component model; the fraction is strictly between zero and one.
  • Mole fraction counts the specified chemical entities. If dissolution changes the species through reaction or dissociation, define the entities and amounts consistently.
  • The molality conversion uses solvent molar mass, not solute molar mass. Enter that value in g/mol; the default molality denominator is kg in metric and lb in imperial settings.

Common questions

Is mole percent the same as mass percent?

No. Mole percent is based on amounts of substance. Mass percent also depends on the component molar masses.

Which molar mass is used for the molality conversion?

The solvent molar mass converts solvent moles into solvent mass, which is the denominator of molality.

References

Bookify requires the solute mole fraction strictly between zero and one for this positive two-component model.

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