Chemistry / Unit 8 Chem 1584 short lesson, about 20 seconds
The van't Hoff Factor
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The idea
The van't Hoff factor is the measured ratio of dissolved particles to formula units dissolved, correcting a colligative calculation for ionization.
In practice
Sodium chloride's factor measures near 1.9, close to but below the 2 predicted for complete dissociation, from residual ion pairing.
Where people slip
A factor visibly below its predicted whole number is not measurement error — it reflects real residual ion-ion attraction in solution.
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