Van 't Hoff factor

In the physical chemistry of the dimensionless van ' t Hoff factor i denotes the relationship which forms the sum of the amounts of a solute ( the solute ) in an aqueous solution with the molar amount of the originally added the starting material.

The factor is thus a measure of the extent to which the dissociated solute and - if it is at least partially dissociated - in the number of particles it is divided in the dissociation. The designation goes to Jacobus Henricus van ' t Hoff back, the first winner of the Nobel Prize for Chemistry.

Importance

The Van ' t Hoff factor is especially important for colligative processes play an important role, since it depends here on the absolute number and not on the nature of the particles. For example, the osmotic pressure of a saline solution is nearly twice as high as that of a sugar solution with the same molar concentration (see examples).

Calculation

The following applies:

• The dissociated fraction of the original amount of substance ( is the degree of dissociation; ) any shares in the solution Walking into a number of particles; it is reflected by the following factor:

• Also, the undissociated portion of the original amount of substance in the solution is counted ( the degree of association ):

Thus, the following applies:

Examples

As an example, glucose has a Van ' t Hoff factor of 1, since it is undissociated soluble in water:

In contrast, the Van ' t Hoff factor of sodium chloride equal to 2, for one mole of NaCl is dissociated substantially completely in a respective mole of Na and Cl-:

Substances such as weak electrolytes dissociate only partially, have a broken van ' t Hoff factor, depending on the dissociation equilibrium.

Swell

• Rompp CD 2006, Georg Thieme Verlag 2006

• Physical chemistry