Colligative properties

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In chemistry, the term colligative property refers to any physical property of a dilute solution dependent on the number of solute particles present, but wholly independent of the solute's identity. Examples of colligative properties include vapor pressure, boiling point, freezing point, and osmotic pressure.

## Contents

* 1 Vapor pressure of a dilute solution
* 2 Boiling point elevation
* 3 Freezing point depression
* 4 Osmotic pressure
* 5 General References

### Vapor pressure of a dilute solution[edit]

The vapor pressure (Pi) of a dilute solution may be determined by Raoult's Law:

Pi=XjP*i

where Xj is the mole fraction of the solute and P*i is the vapor pressure of the pure solvent. The vapor pressure of a dilute solution is a colligative property because the vapor pressure reduction is independent of the solute's identity.

### Boiling point elevation[edit]

Concomitant with a reduction in vapor pressure is the elevation of a dilute solution's boiling point relative to the pure solvent. The relationship between boiling point elevation (ΔT) and the molality (m) of a dilute solution is expressed as follows:

ΔT=Kbm

where Kb is the ebullioscopic constant of the solvent.

### Freezing point depression[edit]

The relationship between freezing point depression (ΔT) and the molality (m) of a dilute solution is expressed as follows:

ΔT=Kfm

where Kf is the cryoscopic constant of the solvent.

### Osmotic pressure[edit]

## General References[edit]

Atkins, P.W. Physical Chemistry (5th ed.), New York: W.H. Freeman and Co, 1994.