Freezing Point Depression

When a solution freezes, the solid is usually pure solvent. Thus the solid-vapor equilibrium (sublimation) P-T curve is unaffected by the presence of solute. The intersection of this curve and the liquid-vapor curve is the triple point (nearly the same temperature as the freezing point, which is measured at atmospheric pressure). Since a solute lowers the solvent vapor pressure, the triple point is shifted to lower temperature, as shown in Figure 1.1. Detailed calculations show that the decrease in freezing point for a dilute solution is proportional to the total molal concentration of solutes

Kfp is the molal freezing-point constant of the solvent. Like K_bp, K_fp is a property of the solvent, independent of the nature of the solutes.

Example

The freezing point of pure camphor is 178.4°C and K_fp = 40.0 K kg/mol. Find the freezing point of a solution containing 1.50 g of a compound of molar mass 125 g/mol in 35.0 g of camphor. The molality of the solution is

Thus

Figure 1.1. Solid-liquid, solid-vapor and liquid-vapor equilibrium curves for pure water (solid curves) and for a solution (dashed curves). The triple point (where solid, liquid, and vapor coexist and at nearly the same temperature as the freezing point) is shifted to lower temperature for the solution.

مواضيع ذات صلة

تطبيقات الامتزاز Applications Of Adsorption

الامتزاز من المحلول ِAdsorption from Solution

أنواع الامتزاز Types of adsorption

البوليمرات الموصلة المالئة Filled Conductive Polymer

البوليمرات الموصلة كهربائياًElectrically Conducting Polymers

المواد فائقة التوصيلية Super Conductors

أشباه الموصلات Semiconductors

المواد العازلة Insulators

الموصلات المعدنية أو الالكترونية Conductors or Metals

التوصيلية والتركيب الالكتروني للمواد الموصل Conductivity and electronic structure of conducting materials

قانون أوم

التوصيلية الكهربائية Electrical Conductivity