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Colligative properties

 
Colligative Properties

 
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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
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
; elevation of boiling point
Boiling-point elevation

Boiling-point elevation describes the phenomenon that the boiling point of a liquid will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent....
; depression of freezing point
Freezing-point depression

Freezing-point depression describes the phenomenon that the Melting point of a liquid is depressed when another compound is added, meaning that a solution has a lower freezing point than a pure solvent....
; osmotic pressure
Osmotic pressure

Osmotic pressure is the Fluid_statics#Hydrostatic_pressure produced by a difference in concentration between solutions on the two sides of a surface such as a differentially permeable membrane....
 (see Osmosis
Osmosis

Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....
; Reverse Osmosis
Reverse osmosis

Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
). Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea
Urea

Urea is an organic compound with the chemical formula 2carbonoxygen.Urea is also known by the International Nonproprietary Name carbamide, as established by the World Health Organization....
 or glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 can lead to accurate determinations of relative molecular masses.






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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
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
; elevation of boiling point
Boiling-point elevation

Boiling-point elevation describes the phenomenon that the boiling point of a liquid will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent....
; depression of freezing point
Freezing-point depression

Freezing-point depression describes the phenomenon that the Melting point of a liquid is depressed when another compound is added, meaning that a solution has a lower freezing point than a pure solvent....
; osmotic pressure
Osmotic pressure

Osmotic pressure is the Fluid_statics#Hydrostatic_pressure produced by a difference in concentration between solutions on the two sides of a surface such as a differentially permeable membrane....
 (see Osmosis
Osmosis

Osmosis is the diffusion of a solvent through a Semipermeable membrane, from a solution of low solute concentration to a solution with high solute concentration , up a solute concentration gradient....
; Reverse Osmosis
Reverse osmosis

Reverse osmosis is a filtration process typically used for water. It works by using pressure to force a solution through a semi-permeable membrane, retaining the solute on one side and allowing the pure solvent to pass to the other side....
). Measurements of these properties for a dilute aqueous solution of a non-ionized solute such as urea
Urea

Urea is an organic compound with the chemical formula 2carbonoxygen.Urea is also known by the International Nonproprietary Name carbamide, as established by the World Health Organization....
 or glucose
Glucose

Glucose , a monosaccharide also known as grape sugar, blood sugar, or corn sugar, is a very important carbohydrate in biology....
 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
Raoult's law

Established by Fran?ois-Marie Raoult, Raoult's law states:Once the components in the solution have reached chemical equilibrium, the total vapor pressure p of the solution is:...
, which states that:
The vapor pressure
Vapor pressure

Vapor pressure , is the pressure of a vapor in Thermodynamic equilibrium with its non-vapor Phase s. All liquids and solids have a tendency to evaporate to a gaseous form, and all gases have a tendency to Condensation back into their original form ....
 of an ideal solution
Ideal solution

In chemistry, an ideal solution or ideal mixture is a solution in which the enthalpy of solution is zero; the closer to zero the enthalpy of solution is, the more "ideal" the behavior of the solution becomes....
 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
Raoult's law

Established by Fran?ois-Marie Raoult, Raoult's law states:Once the components in the solution have reached chemical equilibrium, the total vapor pressure p of the solution is:...
.)


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 + ?Tb
where
?Tb = molality * Kb * i, (Kb = ebullioscopic constant
Ebullioscopic constant

In thermodynamics, the ebullioscopic constant, Kb, allows one to relate molality to boiling point elevation. It is the ratio of the latter to the former:...
, which is 0.51°C kg/mol for the boiling point of water; i = Van 't Hoff factor
Van 't Hoff factor

The van 't Hoff factor is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression....
)


Freezing point depression


Freezing Pointsolution = Freezing Pointsolvent - ?Tf

where :?Tf = molality * Kf * i, (Kf = cryoscopic constant
Cryoscopic constant

In thermodynamics, the cryoscopic constant, Kf, allows one to relate molality to freezing point depression. It is the ratio of the latter to the former:...
, which is -1.86°C kg/mol for the freezing point of water, this is very finr; i = Van 't Hoff factor
Van 't Hoff factor

The van 't Hoff factor is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression....
)

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:

  1. The osmotic pressure
    Osmotic pressure

    Osmotic pressure is the Fluid_statics#Hydrostatic_pressure produced by a difference in concentration between solutions on the two sides of a surface such as a differentially permeable membrane....
     of a dilute solution at constant temperature is directly proportional to its concentration.
  2. The osmotic pressure
    Osmotic pressure

    Osmotic pressure is the Fluid_statics#Hydrostatic_pressure produced by a difference in concentration between solutions on the two sides of a surface such as a differentially permeable membrane....
     of a solution is directly proportional to its absolute temperature.


These are analogous to Boyle's law
Boyle's law

Boyle's law is one of several gas laws and a special case of the ideal gas law. Boyle's law describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system....
 and Charles's Law
Charles's law

In thermodynamics and physical chemistry, Charles's law is a gas laws and specific instance of the ideal gas law, which states that:At constant pressure, the volume of a given mass of an ideal gas increases or decreases by the same factor as its temperature increases or decreases....
 for gases. Similarly, the combined ideal gas law
Ideal gas law

The ideal gas law is the equation of state of a hypothetical ideal gas, first stated by Beno?t Paul ?mile Clapeyron in 1834. The law is derived from the fact that in the ideal state of any gas a given number of its "particles" occupy the same volume, and that volume changes are inverse to pressure changes and linear to temperature changes....
, PV = nRT, has an analog for ideal solutions:

pV = nRTi


where: p = 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
Gas constant

The gas constant is a physical constant which is featured in a large number of fundamental equations in the physical sciences, such as the ideal gas law and the Nernst equation....
; i = Van 't Hoff factor
Van 't Hoff factor

The van 't Hoff factor is a measure of the effect of a solute upon colligative properties, such as vapor pressure, osmotic pressure and freezing point depression....
.