Colligative Properties Calculator Chemistry

Select property and enter data.

What is the Colligative Properties Calculator?

Quick Answer: A tool that calculates the four colligative properties of solutions: relative lowering of vapour pressure, boiling point elevation, freezing point depression, and osmotic pressure. Enter solute and solvent masses, molar mass, and the appropriate constant to see the change in physical properties of the solvent.

Theory of Colligative Properties

Colligative properties depend only on the number of solute particles, not their identity. For a non‑electrolyte (i=1):
1. Relative lowering of vapour pressure: ΔP/P0 = xsolute (mole fraction of solute).
2. Boiling point elevation: ΔTb = i Kb m, where m is molality.
3. Freezing point depression: ΔTf = i Kf m.
4. Osmotic pressure: π = i CRT, where C is molarity.
The tool uses molality (moles of solute per kg of solvent) for boiling/freezing changes and molarity for osmotic pressure. The visual shows a thermometer/beaker with the phase change highlighted.

Step-by-Step Examples

Example 1: Boiling Point Elevation

  1. Select "Boiling Point Elevation". Solute: 5 g urea (M=60 g/mol), solvent: 100 g water, Kb=0.512 K·kg/mol, i=1.
  2. Molality m = (5/60) / 0.1 = 0.833 mol/kg. ΔTb = 1 * 0.512 * 0.833 = 0.426 K. Boiling point rises from 373.15 K to 373.58 K.

Example 2: Freezing Point Depression

  1. Choose "Freezing Point Depression". Same data with Kf=1.86 K·kg/mol. ΔTf = 1.86 * 0.833 = 1.55 K. Freezing point drops to -1.55°C.

Example 3: Osmotic Pressure

  1. Select "Osmotic Pressure". Solute 5 g in 100 mL water (0.1 L). Molarity = (5/60)/0.1 = 0.833 M. π = 1 * 0.833 * 0.0821 * 298 = 20.4 atm.

Frequently Asked Questions

What is the Van't Hoff factor (i)?

It accounts for dissociation of solute into ions. For non‑electrolytes like sugar, i=1. For NaCl, i=2 (complete dissociation).

Why does boiling point increase?

Solute particles lower the vapour pressure of the solvent. To reach atmospheric pressure, a higher temperature is needed, raising the boiling point.

What is molality vs molarity?

Molality (mol/kg solvent) is used for temperature‑dependent properties because it doesn't change with temperature. Molarity (mol/L solution) is used for osmotic pressure.

Can I use grams of solvent directly?

Yes, enter solvent mass in grams. The tool converts to kilograms for molality. For osmotic pressure, you need the solution volume (assumed 100 mL if not provided).

Are the constants correct for any solvent?

The constants Kb and Kf are specific to the solvent. Water: Kb=0.512, Kf=1.86. The tool allows custom values for other solvents.