In thermodynamics, the ebullioscopic constant, K_b, allows one to relate molality to boiling point elevation. It is the ratio of the latter to the former:



i is the Vant Hoff factor. It is determined by whether the solute particles in the solution associate or dissociate.
If all the particles of the solute trimerise (Three associate into one) the Vant hoff factor will be 1/3. If they dissociate into two particles (For example NaCl as solute which breaks into Na⁺ and Cl^-), i=2.



R - Ideal Gas constant

T_b - Boiling point of liquid.

L_v - Latent heat of vaporisation per gram.


Through the procedure called ebullioscopy, a known constant can be used to calculate an unknown molar mass

Molar mass

Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...

. The term "ebullioscopy" comes from the Greek language

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 and means "boiling measurement." This is related to cryoscopy, which determines the same value from the 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:\triangle T_f = K_f \cdot m \cdot i...

 (of freezing point depression).

This property of elevation of boiling point is a colligative property. It means that the property, in this case depends on the number of particles dissolved into the solvent and not the nature of those particles.

Some K_b values

• 0.512 Water
• 5.03 Carbon tetrachloride
  Carbon tetrachloride
  Carbon tetrachloride, also known by many other names is the organic compound with the formula CCl4. It was formerly widely used in fire extinguishers, as a precursor to refrigerants, and as a cleaning agent...
  
  
• 3.63 Chloroform
  Chloroform
  Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
  
  
• 2.53 Benzene
  Benzene
  Benzene is an organic chemical compound. It is composed of 6 carbon atoms in a ring, with 1 hydrogen atom attached to each carbon atom, with the molecular formula C6H6....
  
  
• 2.34 Carbon disulfide
  Carbon disulfide
  Carbon disulfide is a colorless volatile liquid with the formula CS2. The compound is used frequently as a building block in organic chemistry as well as an industrial and chemical non-polar solvent...
  
  
• 2.02 Diethyl ether
  Diethyl ether
  Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
  
  
• 5.95 Camphor
  Camphor
  Camphor is a waxy, white or transparent solid with a strong, aromatic odor. It is a terpenoid with the chemical formula C10H16O. It is found in wood of the camphor laurel , a large evergreen tree found in Asia and also of Dryobalanops aromatica, a giant of the Bornean forests...
  
  
• 3.08 Acetic acid
  Acetic acid
  Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
  
  
• 2.79 Cyclohexane
  Cyclohexane
  Cyclohexane is a cycloalkane with the molecular formula C6H12. Cyclohexane is used as a nonpolar solvent for the chemical industry, and also as a raw material for the industrial production of adipic acid and caprolactam, both of which being intermediates used in the production of nylon...
  
  
• 1.07 Ethanol
  Ethanol
  Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
  
  

See also

• Ebullioscope
  Ebullioscope
  An ebullioscope is an instrument for measuring the boiling point of a liquid. This can be used for determining the alcoholic strength of a mixture, or for determining the molecular weight of a non-volatile solute based on the boiling-point elevation...
  
  
• List of boiling and freezing information of solvents
• Boiling-point elevation
  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. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such...
  
  
• Colligative Properties
  Colligative properties
  Colligative properties are properties of solutions that depend on the number of molecules in a given volume of solvent and not on the properties/identity of the molecules. Colligative properties include: relative lowering of vapor pressure; elevation of boiling point; depression of freezing point...