The colligative properties calculator computes all four colligative properties in one place: boiling point elevation (ΔTb), freezing point depression (ΔTf), osmotic pressure (π), and vapor pressure lowering (ΔP). Enter the solute molality or molarity plus the van't Hoff factor and solvent constants to get instant results for AP Chemistry, general chemistry, and physical chemistry problems.
Solution Parameters
1=nonelectrolyte, 2=NaCl, 3=CaCl₂
Quick presets:
Results
Boiling Point Elevation (ΔTb)
°C above normal boiling point
Freezing Point Depression (ΔTf)
°C below normal freezing point
Osmotic Pressure (π)
atm
Vapor Pressure Lowering (ΔP)
mmHg
New Boiling Point
New Freezing Point
Formulas Used
Calculation Summary
| Property | Formula | Result |
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How to Use the Colligative Properties Calculator
This colligative properties calculator handles all four solution properties that depend on the concentration of solute particles, not their chemical identity. Whether you need the boiling point elevation for a sugar solution or the osmotic pressure of a saline IV, this tool covers all four in one calculation.
What You Need to Enter
Select your solvent from the dropdown (water, benzene, acetic acid, cyclohexane, or chloroform — or enter custom constants). Enter the molality for ΔTb and ΔTf calculations, molarity and temperature for osmotic pressure, and mole fraction of solute for vapor pressure lowering. Set the van't Hoff factor: 1 for glucose and other non-electrolytes, 2 for NaCl or KCl, 3 for CaCl₂.
The Four Formulas
Boiling point elevation: ΔTb = i × Kb × m — the solution boils higher than the pure solvent. Water with 1 molal NaCl (i=2) boils at 101.024°C instead of 100°C.
Freezing point depression: ΔTf = i × Kf × m — the solution freezes lower. This is why antifreeze (ethylene glycol, i=1) at 5 molal in water freezes at −9.3°C rather than 0°C.
Osmotic pressure: π = iMRT, where R = 0.08206 L·atm/(mol·K). A 1 M glucose solution at 25°C (298 K) has π ≈ 24.4 atm — roughly 250 times atmospheric pressure. This is why IV saline must be carefully concentration-matched to blood plasma.
Vapor pressure lowering: ΔP = x₂ × P° (Raoult's law, non-electrolyte approximation). A solution with x₂ = 0.01 mole fraction solute in water at 25°C (P° = 23.8 mmHg) has its vapor pressure lowered by 0.238 mmHg.
Worked Example: Road Salt
NaCl (i = 2) at 1 molal in water: ΔTf = 2 × 1.86 × 1.0 = 3.72°C. The new freezing point is 0 − 3.72 = −3.72°C. At 2 molal: −7.44°C. At 5 molal: −18.6°C — which is why concentrated brine effectively de-ices roads down to about −18°C.
Solvent Constants Reference
The ebullioscopic constant (Kb) and cryoscopic constant (Kf) differ by solvent. Water has Kb = 0.512°C·kg/mol and Kf = 1.86°C·kg/mol, making it one of the smallest-constant solvents. Cyclohexane has Kf = 20.2, meaning even small solute concentrations cause large freezing point changes — useful for molecular weight determination.
FAQ
What are colligative properties?
Colligative properties are solution properties that depend only on the number of solute particles, not their identity. The four main colligative properties are boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering.
Is this calculator free?
Yes, completely free with no signup or account required. All calculations run in your browser.
Is my data private?
Yes. All calculations run locally in your browser. No data is sent to any server.
What is the van't Hoff factor (i)?
The van't Hoff factor (i) accounts for ionization — the number of particles a formula unit produces in solution. For non-electrolytes like glucose, i = 1. For NaCl (Na⁺ + Cl⁻), i = 2. For CaCl₂ (Ca²⁺ + 2Cl⁻), i = 3. Higher i means greater colligative effect.
What is molality and why is it used for colligative properties?
Molality (m) is moles of solute per kilogram of solvent. It's temperature-independent, unlike molarity, making it the correct concentration unit for colligative property calculations. Even at 100°C boiling water, the molality doesn't change.
How does osmotic pressure work?
Osmotic pressure (π = iMRT) is the pressure needed to stop solvent from flowing through a semipermeable membrane from dilute to concentrated solution. It uses molarity (M) rather than molality, and R = 0.08206 L·atm/(mol·K) or 8.314 J/(mol·K).
Why do roads use salt to melt ice?
Salt (NaCl, i = 2) dissolved in water depresses the freezing point by 2 × 1.86°C per molal unit. A 1 molal NaCl solution freezes at about −3.72°C instead of 0°C. This is freezing point depression — a colligative property that makes salt effective for de-icing down to roughly −10°C.