I keep getting “van't Hoff factor (i)” questions wrong in Solutions & Colligative Properties. What's the trap?
ignoring dissociation, so predicting equal effects for salt and sugar.
The usual trap: ignoring dissociation, so predicting equal effects for salt and sugar. How to avoid it: multiply the colligative effect by i for anything that dissociates. Go back to the definition — the number of particles one formula unit gives in solution — about 2 for NaCl, 3 for CaCl₂, 1 for glucose.
Key point
van't Hoff factor (i)
Common mistake
ignoring dissociation, so predicting equal effects for salt and sugar.
Memory tip
multiply the colligative effect by i for anything that dissociates.
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