<Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2009) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article does not cite any sources . Please help improve this article by adding citations to reliable sources . Unsourced material may be challenged and removed . (January 2009) (Learn how and when to remove this template message) </Td> </Tr> <P> The van&nbsp 't Hoff factor i (named after Dutch chemist Jacobus Henricus van' t Hoff) is a measure of the effect of a solute upon colligative properties such as osmotic pressure, relative lowering in vapor pressure, boiling - point elevation and freezing - point depression . The van' t Hoff factor is the ratio between the actual concentration of particles produced when the substance is dissolved and the concentration of a substance as calculated from its mass . For most non-electrolytes dissolved in water, the van' t Hoff factor is essentially 1 . For most ionic compounds dissolved in water, the van' t Hoff factor is equal to the number of discrete ions in a formula unit of the substance . This is true for ideal solutions only, as occasionally ion pairing occurs in solution . At a given instant a small percentage of the ions are paired and count as a single particle . Ion pairing occurs to some extent in all electrolyte solutions . This causes the measured van' t Hoff factor to be less than that predicted in an ideal solution . The deviation for the van' t Hoff factor tends to be greatest where the ions have multiple charges . </P> <P> The degree of dissociation is the fraction of the original solute molecules that have dissociated . It is usually indicated by the Greek symbol α (\ displaystyle \ alpha). There is a simple relationship between this parameter and the van' t Hoff factor . If a fraction α (\ displaystyle \ alpha) of the solute dissociates into n (\ displaystyle n) ions, then </P>

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