Colligative properties
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'''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]]; [[Boiling-point elevation|elevation of boiling point]]; [[Freezing-point depression|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.
==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 Point<sub>total</sub> = Boiling Point<sub>solvent</sub> + ΔT<sub>b</sub>
where
:ΔT<sub>b</sub> = [[molality]] * K<sub>b</sub> * ''i'', (K<sub>b</sub> = ebullioscopic constant, which is 0.51 K kg/mol for the boiling point of water; ''i'' = [[Van 't Hoff factor]])
===Freezing point depression ===
Freezing Point<sub>total</sub> = Freezing Point<sub>solvent</sub> - ΔT<sub>f</sub>
where :ΔT<sub>f</sub> = [[molality]] * K<sub>f</sub> * ''i'', (K<sub>f</sub> = 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 [[van't Hoff|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 = nRT''i''
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]].
[[Category:Solutions]]
[[Category:Physical chemistry]]
[[ca:Propietat col·ligativa]]
[[de:Kolligative Eigenschaft]]
[[es:Propiedad coligativa]]
[[hu:Kolligatív sajátság]]
[[ja:束一的性質]]
[[pt:Propriedades coligativas]]
[[sv:Kolligativa egenskaper]]