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Van 't Hoff factor
In physical chemistry, the van 't Hoff factor i is the number of moles of solute actually in solution per mole of solid solute added. Equivalently, i refers to the ratio of true molecular mass to calculated molecular methods by colligative methods. It is named after Jacobus Henricus van 't Hoff, the winner of the first Nobel Prize in chemistry.
Additional recommended knowledge
Physical significance of i
In NaCl for example, i = 2 indicates that by using the colligative properties equations without the i factor, we're actually calculating the molar mass of each of the Na+ and Cl- ions in solution. The molar mass of NaCl should be twice that number because it originally dissociated to produce one Na+ ion and one Cl- ion per formula unit of NaCl; the sum of the masses of the two ions should yield the mass of one formula unit of NaCl. Note that even if the mass of Na+ and Cl- weren't equal (which is the case), we're only calculating the average mass of the two particles using our colligative properties analysis. Hence multiplying that average number by two, we would be calculating the molar mass of NaCl.
Relation to degree of dissociation
Where α is the degree of association/ dissociation and n is the number of particles produced during association or dissociation per molecule or formula unit of the solute.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Van_'t_Hoff_factor". A list of authors is available in Wikipedia.|