Ion Activity

Definition

The effective concentration of an ion that accounts for interactions in solution, which can diverge significantly from measured concentration.

Ksp defines its solubility boundary in terms of ion activity rather than concentration. In real waters activity can diverge from concentration, leading to poor solubility estimates from concentration alone. This divergence is why the industry relies on empirical scale indices rather than direct Ksp calculation.

Related concepts

Solubility Product Constant · Scale Indices · Concentration as Scale Driver

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Part of The Blueprint of Water · 📏 measurement