Van 't Hoff factor

In physical chemistry, the Van 't Hoff factor i is the number of moles of solute actually in a solution in water, per mole of solid solute added. It is named after Jacobus Henricus van 't Hoff, the first winner of the Nobel Prize in chemistry.

Related Topics:
Physical chemistry - Solute - Solution - Jacobus Henricus van 't Hoff - Nobel Prize in chemistry

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For example, glucose has a Van 't Hoff Factor of 1 because one mole of glucose dissolved in water will result in one mole dissolved. The Van 't Hoff Factor of sodium chloride is 2 because one mole will dissociate completely into one mole of Na+ and one mole of Cl- for a total of 2 moles. Substances that dissociate partially, such as acetic acid have a fractional Van 't Hoff factor, which is an average of the different dissociation states, weighted for the occurrence of each. That for acetic acid is just over 1 (representing the equlibrium between HC2H3O2 and the ions H+ and C2H3O2-)

Related Topics:
Glucose - Sodium chloride - Acetic acid

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The Van 't Hoff factor can be calculated by the formula i = 1 + lphaleft(q - 1 ight), where α is the degree of ionization and q is the number of ions formed for each dissociated molecule. For example, for a sulfuric acid (H2SO4) solution, in which 64% of the molecules are ionized, i could be calculated by i = 1 + left(0.64 ight)left(3 - 1 ight) = 2.28, as each molecule results in one sulfate ion and two hydronium ions. That same result could be achieved by realizing that, for each 100 molecules of acid, 36 are kept and 64 are ionized, resulting in 192 ions and 36 molecules, adding up to a total of 228 particles. Therefore, there would be 2.28 times as many ions as there were acid molecules before.

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The Van 't Hoff factor is important in quantitative analysis of colligative properties, such as vapor pressure and freezing point depression.

Related Topics:
Colligative properties - Vapor pressure - Freezing point depression

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