Raoult's Law Calculator

What the Raoult's Law Calculator does

Use this page when solvent mole fraction and pure-solvent vapor pressure are known.

Raoult's Law Calculator keeps the calculation local in the browser session and reports both the primary result and supporting context. The page separates formula, assumptions, examples, warnings and references so the result is easier to audit.

Formula and variables

P_solution = x_solvent x P_pure.

• P_solution is solution vapor pressure
• x_solvent is solvent mole fraction
• P_pure is pure-solvent vapor pressure

Step-by-step worked example

Use the default calculator values as the worked example for Raoult's Law Calculator. After Calculate, the result card shows the substituted formula and a table with the same values used by the engine.

The example is intentionally simple so the unit conversion and formula direction are visible. More advanced chemistry problems should still be checked against class conventions or laboratory procedure.

• x solvent = 0.80, P pure = 100 mmHg gives P solution = 80 mmHg
• Lower solvent mole fraction lowers vapor pressure
• Multiple volatile components require summing component vapor pressures

Additional examples

These examples are covered by the Chemistry Phase 1 test fixtures or by the same calculation path.

• x solvent = 0.80, P pure = 100 mmHg gives P solution = 80 mmHg
• Lower solvent mole fraction lowers vapor pressure
• Multiple volatile components require summing component vapor pressures

How to read the dynamic chemistry visual

The visual for this page is a liquid mixture vapor-pressure contribution visual. It is not shown before Calculate, so no fake default result appears.

After a valid calculation, the visual includes the current output and concept labels. Visual proportions are normalized for readability, so treat them as explanation aids rather than physical measurements.

Common mistakes

Most errors come from using the wrong unit, selecting the wrong mode or applying a formula outside its assumptions.

• Using solute mole fraction instead of solvent mole fraction.
• Entering percent as 80 instead of 0.80.
• Applying ideal-solution behavior to strongly nonideal mixtures.

Assumptions and limitations

Chemistry formulas are compact models. They are useful for coursework and planning, but real samples, laboratory glassware, purity, temperature and activity effects can change measured values.

• The solution behaves ideally.
• The selected vapor pressure is for the pure solvent at the same temperature.
• Mole fraction is between 0 and 1.
• Nonideal mixtures can show positive or negative deviations.
• Multi-component vapor pressures need each volatile component.

Practical and lab-safety note

This calculator provides educational chemistry calculations from the values and assumptions you enter. It does not replace laboratory measurement, instructor guidance, safety procedures, chemical compatibility checks or professional analysis.

For lab preparation, verify chemical identity, hydration state, concentration standardization, significant figures and safety data before using a result.

Frequently asked questions

References

• IUPAC Gold Book, mole. Relevance: mole definition and Avogadro constant relation. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Formula Mass and the Mole Concept. Relevance: formula mass, molar mass and mole calculations. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Molarity. Relevance: concentration and dilution equations. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Quantitative Chemical Analysis. Relevance: titration and stoichiometric concentration relationships. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, pH and pOH. Relevance: hydrogen ion, hydroxide ion, pH and pOH formulas. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Buffers. Relevance: Henderson-Hasselbalch buffer estimates. Last verified: July 22, 2026. Source.
• NIST Special Publication 811, Guide for the Use of the International System of Units. Relevance: SI units and unit symbols. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Ideal Gas Law. Relevance: PV = nRT, gas density and gas-state unit relationships. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Gaseous Mixtures. Relevance: gas density and Dalton partial-pressure calculations. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Solubility. Relevance: Henry's Law and dissolved gas pressure relationships. Last verified: July 22, 2026. Source.
• OpenStax Chemistry 2e, Colligative Properties. Relevance: Raoult's Law, boiling point elevation and freezing point depression. Last verified: July 22, 2026. Source.

Chemistry references and local atomic-weight data reviewed on July 22, 2026.