This MedLibrary.org supplementary page on Colligative properties is provided directly from the open source Wikipedia as a service to our readers. Please see the note below on authorship of this content, as well as the Wikipedia usage guidelines. To search for other content from our encyclopedia supplement, please use the form below:
Related Sponsors
 |
This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unverifiable material may be challenged and removed. (March 2008) |
Colligative properties are properties of solutions that depend on the number of particles in a given volume of solvent and not on the mass of the particles. Colligative properties include: lowering of vapor pressure; elevation of boiling point; depression of freezing point; osmotic pressure (see Osmosis; Reverse Osmosis). Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea or glucose can lead to accurate determinations of relative molecular masses. Alternatively, measurements for ionized solutes can lead to an estimation of the percentage of ionization taking place.
Contents |
Vapor pressure
The relationship between the lowering of vapor pressure and concentration is given by Raoult's law, which states that:
- The vapor pressure of an ideal solution is dependent on the vapor pressure of each chemical component and the mole fraction of the component present in the solution. (For details, see the article on Raoult's law.)
Boiling point and freezing point
Both the boiling point elevation and the freezing point depression are proportional to the lowering of vapor pressure in a dilute solution
Boiling point elevation
- Boiling Pointtotal = Boiling Pointsolvent + ΔTb
where
- ΔTb = molality * Kb * i, (Kb = ebullioscopic constant, which is 0.51 K kg/mol for the boiling point of water; i = Van 't Hoff factor)
this content is provided by vikash kumar.
Freezing point depression
Freezing Pointtotal = Freezing Pointsolvent - ΔTf
where :ΔTf = molality * Kf * i, (Kf = cryoscopic constant, which is 1.86 K kg/mol for the freezing point of water; i = Van 't Hoff factor)
Osmotic pressure
Two laws governing the osmotic pressure of a dilute solution were discovered by the German botanist W. F. P. Pfeffer and the Dutch chemist J. H. van’t Hoff:
- The osmotic pressure of a dilute solution at constant temperature is directly proportional to its concentration.
- The osmotic pressure of a solution is directly proportional to its absolute temperature.
These are analogous to Boyle's law and Charles's Law for gases. Similarly, the combined ideal gas law, PV = nRT, has an analog for ideal solutions:
- πV = nRTi
where: π = osmotic pressure; V is the volume; T is absolute temperature; n is the number of moles of solute; R = 8.3145 J K-1mol-1, the molar gas constant; i = Van 't Hoff factor.
Wikipedia content modification information:
- This page was last modified on 3 September 2008, at 13:30.
Wikipedia Authorship and Review
Wikipedia content provided here is not reviewed directly by MedLibrary.org. Wikipedia content is authored by an open community of volunteers and is not produced by or in any way affiliated with MedLibrary.org.
Wikipedia Usage Guidelines
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article on "Colligative properties".
The URL for this specific entry is:
All Wikipedia text is available under the terms of the GNU Free Documentation License. (See Copyrights for details). Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc.