Colligative properties calculator — boiling, freezing

Chemistry · Solutions

Boiling-point elevation, freezing-point depression and osmotic pressure

Enter solute mass, molar mass, van’t Hoff factor, and solvent data to compute molality, ΔTb, ΔTf, and π. You can also switch to molar-mass mode to estimate an unknown M from measurements. A useful class exercise is comparing a 1.0 m non-electrolyte with an ideal NaCl case (i ≈ 2).

How to use (3 steps)

Choose the mode: property calculation (ΔTb, ΔTf, π) or molar mass from colligative data.
Start from the water example or select another solvent, then adjust solute mass, molar mass, i, volumes and temperature.
Read off the summary and step-by-step log, then copy the URL to share the exact scenario with students or colleagues.

All calculations run in your browser only; no solute, solvent or result data are sent to any server.

Inputs

Use grams for masses, litres for volumes and kelvins for temperature. The default water example corresponds to a 1.0 m non-electrolyte solution.

Quick examples:

Property mode (ΔTb, ΔTf, π) Molar mass from colligative data

Solvent

Choosing a preset fills Kb, Kf, Tb⁰ and Tf⁰ for you; you can still edit the constants manually.

Solvent name

Boiling-point elevation constant Kb (K·kg/mol)

Freezing-point depression constant Kf (K·kg/mol)

Pure solvent boiling point Tb⁰ (°C)

Pure solvent freezing point Tf⁰ (°C)

Solute name

Molar mass M (g/mol)

van’t Hoff factor i

For a non-electrolyte, take i = 1. For NaCl that dissociates ideally into two ions, i ≈ 2.

Solute mass (g)

Solvent mass (g)

Solution volume (L, optional for π)

Temperature T (K) for π

Results

Mode: Property mode (ΔTb, ΔTf, π)

Colligative data: From boiling-point elevation ΔTb

This section summarizes molality, colligative changes (ΔTb, ΔTf, π) and, in molar-mass mode, the estimated molar mass M consistent with your measurements.

How it's calculated

Steps will appear here after calculation.

Formulas (LaTeX)

Use these LaTeX forms for handouts, slides, or worked examples. They follow the same sign and unit conventions as this calculator.

How to use this calculator

Use property mode when you know the masses of solute and solvent and want ΔTb, ΔTf, or osmotic pressure. Switch to molar-mass mode when you already measured one colligative property and want to infer the molar mass that would explain the observation.

What to enter

ΔTb and ΔTf use molality, so you need solute mass, solvent mass, molar mass, and van’t Hoff factor. Osmotic pressure additionally needs solution volume and temperature because it uses molarity instead of molality.

Important edge cases

A zero-solute case is valid and represents the pure-solvent limit. If you enter Kb, Kf, volume, or temperature explicitly, they must be positive; leave them blank only when you intend to skip that property.

Recommended next checks

Confirm whether your sample behaves ideally before choosing the van’t Hoff factor.
Keep solvent mass and solution volume separate; they are not interchangeable.
If you infer molar mass from π, verify the temperature and volume measurement before comparing with literature values.

FAQ

What are colligative properties?

Colligative properties depend mainly on the number of dissolved particles, not their identity. Common examples are boiling-point elevation, freezing-point depression, vapour-pressure lowering, and osmotic pressure. This tool focuses on ΔTb, ΔTf, and π for simple dilute solutions.

Can I use electrolytes with this tool?

Yes. Set van’t Hoff factor i to the effective particle count per formula unit, such as i ≈ 2 for ideal NaCl and i ≈ 3 for ideal CaCl₂. For concentrated or strongly non-ideal solutions, this model is only an approximation.

What is the difference between molality m and molarity c?

Molality m is moles of solute per kilogram of solvent (mol/kg). Molarity c is moles of solute per litre of solution (mol/L). This calculator uses molality for ΔTb and ΔTf, and molarity with temperature for π. In practice, enter masses for solute and solvent, then add solution volume and temperature only when you need π.

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