ebullioskopi

Ebullioscopy is a colligative property of solutions. It refers to the rise in the boiling point of a solvent when a solute is added. This phenomenon is a direct consequence of the solute's presence, which lowers the vapor pressure of the solvent. According to Raoult's law, the vapor pressure of a solution is proportional to the mole fraction of the solvent. By lowering the solvent's vapor pressure, the solute makes it necessary to reach a higher temperature to achieve a vapor pressure equal to the external atmospheric pressure, which is the definition of boiling.

The extent of the boiling point elevation is directly proportional to the molality of the solute. This relationship is expressed by the ebullioscopic formula: ΔTb = Kb * m, where ΔTb is the boiling point elevation, Kb is the ebullioscopic constant of the solvent (a characteristic property of each solvent), and m is the molality of the solution (moles of solute per kilogram of solvent). Ebullioscopy can be used to determine the molar mass of an unknown non-volatile solute. By measuring the boiling point elevation of a solution of known concentration, and knowing the ebullioscopic constant of the solvent, the molality can be calculated. From the molality, the number of moles of the solute can be determined, and subsequently, its molar mass can be found if the mass of the solute is known. This method is particularly useful for non-volatile organic compounds.