Colligative Properties Calculator

Calculate boiling point elevation, freezing point depression, osmotic pressure, and vapor pressure lowering for solutions.

Boiling Point
Freezing Point
Osmotic Pressure
Vapor Pressure
Moles of solute per kg of solvent
Boiling point elevation constant for the solvent
For water: 100°C
Number of particles the solute dissociates into
Moles of solute per kg of solvent
Freezing point depression constant for the solvent
For water: 0°C
Number of particles the solute dissociates into
Moles of solute per liter of solution
Number of particles the solute dissociates into
Moles of solute divided by total moles
For water at 25°C: 23.8 mmHg
Number of particles the solute dissociates into
Calculating...
Colligative Properties Calculation Results

Understanding Colligative Properties

Colligative properties are properties of solutions that depend on the ratio of the number of solute particles to the number of solvent molecules in a solution, and not on the nature of the chemical species present. These properties include:

Key Insight: Colligative properties are proportional to the concentration of solute particles, not their identity. This makes them particularly useful for determining molecular weights of unknown compounds.

The Four Colligative Properties

1

Vapor Pressure Lowering: The presence of a non-volatile solute lowers the vapor pressure of a solvent. Described by Raoult's Law: P = Xsolvent × P°

2

Boiling Point Elevation: Adding a solute increases the boiling point of a solvent. The change is given by: ΔTb = i × Kb × m

3

Freezing Point Depression: Adding a solute decreases the freezing point of a solvent. The change is given by: ΔTf = i × Kf × m

4

Osmotic Pressure: The pressure required to prevent osmosis. Described by: π = i × M × R × T

Common Solvent Constants

Solvent Kb (°C/m) Kf (°C/m) Boiling Point (°C) Freezing Point (°C)
Water 0.512 1.86 100.0 0.0
Benzene 2.53 5.12 80.1 5.5
Acetic Acid 3.07 3.90 118.1 16.6
Chloroform 3.63 4.70 61.2 -63.5
Ethanol 1.22 1.99 78.4 -114.6
Carbon Tetrachloride 5.03 29.8 76.8 -22.8

Van't Hoff Factor (i)

The Van't Hoff factor represents the number of particles a solute dissociates into in solution. For example:

  • Non-electrolytes (sucrose, glucose): i = 1 (no dissociation)
  • Strong electrolytes (NaCl, KCl): i = 2 (dissociates into 2 ions)
  • Strong electrolytes (CaCl2, MgCl2): i = 3 (dissociates into 3 ions)
  • Weak electrolytes: i is between 1 and the theoretical maximum (depends on degree of dissociation)

Practical Application: Colligative properties have numerous real-world applications, including antifreeze in car radiators, salting icy roads, preserving food, and in medical applications like intravenous solutions.

Frequently Asked Questions

Colligative properties are properties of solutions that depend on the concentration of solute particles but not on their identity. The four main colligative properties are vapor pressure lowering, boiling point elevation, freezing point depression, and osmotic pressure.

When salt dissolves in water, it dissociates into ions that disrupt the formation of the crystalline ice structure. This makes it harder for water molecules to arrange into a solid, requiring a lower temperature to freeze. The freezing point depression is proportional to the molality of the salt solution.

The Van't Hoff factor (i) represents the number of particles a solute dissociates into when dissolved. For non-electrolytes like sugar, i=1. For strong electrolytes like NaCl, i=2 (as it dissociates into Na+ and Cl- ions). For CaCl2, i=3 (as it dissociates into Ca2+ and two Cl- ions).

Intravenous solutions are carefully formulated to match the osmotic pressure of blood (isotonic solutions). If an IV solution has higher osmotic pressure (hypertonic), it would draw water out of blood cells, causing them to shrink. If it has lower osmotic pressure (hypotonic), water would enter the cells, causing them to swell and potentially burst.

Molality (moles solute/kg solvent) is used because it doesn't change with temperature, whereas molarity (moles solute/L solution) does change with temperature due to thermal expansion. Since boiling and freezing points are temperature-dependent properties, molality provides a more consistent measure of concentration.