Colligative properties 456234 224421009 2008-07-08T19:45:04Z Thijs!bot 1392310 robot Adding: [[ca:Propietat col·ligativa]] {{unreferenced|date=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]]; [[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]]