Ionic strength

Ionic strength measures the concentration of dissolved ions, weighting each ion by the square of its charge. It summarizes how strongly ions influence electrostatic interactions in a solution.

Ionic atmosphere: The uneven distribution of surrounding ions around a charged particle in an electrolyte solution. Ionic strength controls how strongly surrounding ions screen a central charge.
Electrolyte: A substance that produces mobile ions when dissolved or molten, enabling electrical conduction. Ionic strength summarizes the ions supplied by dissolved electrolytes.
Buffer solution: A solution that resists changes in pH when modest amounts of acid or base are added. Ionic strength affects activity-based pH calculations and can shift measured equilibria.
Ionic concentration: The concentration of a specified ion or, in broader use, the total concentration of ions in solution. Unlike an unweighted total, ionic strength gives multivalent ions greater influence.
Debye length: A characteristic distance over which electrostatic interactions are screened in an electrolyte. Increasing ionic strength shortens this distance, weakening long-range electrostatic effects.
Ion: An atom or molecule with a net electric charge from losing or gaining electrons. Each dissolved ion contributes according to its concentration and squared charge.
Solubility equilibrium: The equilibrium between a dissolved substance and its undissolved solid phase. Activity corrections involving ionic strength can change predicted solubilities.
Electrolyte concentration: The amount of dissolved electrolyte per unit volume or mass of solution. Equal electrolyte concentrations can produce different ionic strengths when dissociation or ion charges differ.
Activity coefficient: The factor relating a species’ thermodynamic activity to its concentration. Ionic strength helps determine how far ion activities depart from concentrations.
Molar concentration: The amount of a substance, in moles, per unit volume of solution. The standard ionic-strength formula uses each ion’s molar concentration.

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