The number of particles a solute produces in solution, correcting colligative formulas for electrolytes.
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The van't Hoff factor i is the effective number of particles produced when one formula unit of a solute dissolves in a solvent. It corrects the colligative property equations for solutes that dissociate into ions or associate into aggregates. For a strong electrolyte the ideal value equals the number of ions per formula unit, so i = 2 for NaCl and i = 3 for CaCl2, while nonelectrolytes such as glucose have i = 1. In real solutions the measured i is slightly less than the ideal value, because ions pair and interact at higher concentrations. Association of solute molecules gives i less than 1.
Key ideas: Compute ideal i by counting ions: glucose 1, NaCl 2, CaCl2 3, Al2(SO4)3 5, K3[Fe(CN)6] 4. For partial dissociation of a weak electrolyte, i = 1 + alpha (n - 1). For association, i = 1 - alpha/2 for dimers. Measured i approaches the ideal value as the solution becomes more dilute.
Common mistakes and connections: Students use ideal i without considering weak electrolytes like acetic acid, which has i barely above 1. Another error is counting charges rather than ions or forgetting polyatomic ions stay together. Ion pairing explains deviations at higher concentration. Links to colligative property equations, electrolytes and degrees of dissociation.
The van't Hoff factor i counts particles per formula unit: about 1 for glucose, nearly 2 for NaCl, nearly 3 for CaCl2. The interactive lesson shows this as a live animation or chart.
A 0.1 molal NaCl solution has a measured van't Hoff factor of about 1.9, slightly below the ideal value of 2.
The number of particles a solute produces in solution, correcting colligative formulas for electrolytes.
van't Hoff Factor is a advanced topic in States of Matter & Solutions. It builds on beginner and intermediate topics, so review those first if needed.
Study these earlier topics in States of Matter & Solutions first: Osmosis, Osmotic Pressure, Reverse Osmosis.
The next topics in States of Matter & Solutions are Abnormal Molar Mass and Colloids.
Yes. The interactive lesson includes a self-check question on van't Hoff Factor, and the States of Matter & Solutions quiz draws on every topic in this area.
van't Hoff Factor is topic 93 of 109 in States of Matter & Solutions.