highionicstrength

High ionic strength refers to solution conditions in which the ionic strength I is large. In solution chemistry, ionic strength is defined as I = 1/2 sum c_i z_i^2, where c_i is the molar concentration and z_i the charge of each ionic species. High ionic strength typically denotes values on the order of 0.5 M or greater and is commonly encountered in seawater, brines, and concentrated electrolyte solutions.

At high I, electrostatic interactions between ions are screened and the activity coefficients gamma_i depart from unity, leading to changes in ion activities that are not captured by concentration alone. The Debye length, a measure of the effective range of electrostatic forces, shortens as I increases, reducing long-range ion–ion interactions.

Consequences span multiple properties. Solubility and precipitation equilibria depend on activity coefficients; high ionic strength can promote salting-out of certain solutes or, in other cases, stabilize otherwise poorly soluble species. Reaction rates can be altered through changes in ionic strength, affecting ion pairing and transition-state stabilization. In biology, high salt can cause protein precipitation or alter macromolecular stability and aggregation.

Modeling high ionic strength requires beyond-ideal theories. The Debye–Hückel equation is limited in concentrated solutions; extended Debye–Hückel, Davies, and, for very high I, Pitzer models are used to estimate activity coefficients and equilibrium constants.

Common contexts include industrial crystallization, desalination brines, biochemical buffers with high salt, and electrochemical systems where shielding and double-layer properties influence electrode processes.