Freezing-point depression

From Biocrawler, the free encyclopedia.

Freezing-point depression is the difference between the freezing points of a pure solvent and a solution of a nonelectrolyte in that solvent. It is directly proportional to the molal concentration of the solution according to the equation:

freezing-point depression = i · K_f · molality

• molality is in units of mol/kg
• K_f, the freezing-point depression constant is a colligative property.
  • K_f for water is 1.86 K·kg/mol which means that per mole of solute dissolved in a kilogram of water the freezing point depression is 1.86 kelvins.
• i is the i factor or the van 't Hoff i factor see van 't Hoff
  • i is the factor that takes into account the presence of ions in a solution, it indicates the number of particles formed.

Examples:

• i = 1 for sugar in water
• i = 2 for NaCl in water
• i = 3 for CaCl₂ in water
• i = 2 for HCl in water (complete dissociation)
• i = 1 for HCl in benzene (no dissociation)

Wikipedia (http://en.wikipedia.org/wiki/Main_Page) Freezing-point_depression (http://en.wikipedia.org/wiki/Freezing-point_depression) version history (http://en.wikipedia.org/w/index.php?title=Freezing-point_depression&action=history) GNU Free Documentation Lizenz (http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License) CC-by-sa (http://creativecommons.org/licenses/by-sa/2.5/)

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