how can we calculate vanta hoff factor of organic compounds

Asked by  | 13th Jul, 2008, 03:59: PM

Expert Answer:

The number of moles of particles per mole of solute is the van't Hoff factor. Theoretically, you should be able to determine this from the formula of strong electrolyte. For example, since 1 mole of K2S dissociates into 2 moles of potassium ion and 1 mole of sulfide ion, its van't Hoff factor should be 3. However, because ions often associate with each other in solution, forming ion pairs, the true van't Hoff factor is often less than its theoretical value. True van't Hoff factors can be calculated from any of the colligative properties, by adding the van't Hoff factor i to the equation. (e.g., T = iKm). If the van't Hoff factor is used in the equation, the concentration refers to the moles of overall solute rather than to moles of particles.

When a solute is dissolved in a solvent, the boiling point of the solution is raised according to the equation:

T = change in temperature
i = the van't Hoff factor, which is the number of particles into which the solute dissociates
m = the molality, which is the moles of solute per kilograms of solvent
Kb = the molal boiling point constant (for water, Kb = 0.515C/m)


The van't Hoff factor is an important factor in the extent of the change in boiling point or freezing point of a solution after solute has been added.  For substances that do not dissociate in water, such as sugar (C12H22O11), has an i value of 1.  Substances that dissociate in water to give two ion particles, such as salt (NaCl), have an i value of 2.  This pattern continues for any number of particles into which a solute can dissociate.

Answered by  | 14th Jul, 2008, 05:09: PM

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