# Ionic strength

﻿
Ionic strength

The ionic strength, "I", of a solution is a function of the concentration of "all" ions present in a solution.

m B}=1}^{n} c_{ m B}z_{ m B}^{2}

where "c"B is the molar concentration of ion B (mol dm-3), "z"B is the charge number of that ion, and the sum is taken over all ions in the solution. For a 1:1 electrolyte such as sodium chloride, the ionic strength is equal to the concentration, but for MgSO4 the ionic strength is four times higher. Generally multivalent ions contribute strongly to the ionic strength.

For example the ionic strength of a mixed 0.0050M Na2SO4 + 0.0020M NaCl solution is :

I = 1/2(2 * (+1)2 * 0.005) + (+1)2 * 0.0020 + (-2)2 * 0.005 + (-1)2 * 0.002)= 0.017M

Because in non-ideal solutions volumes are no longer strictly additive it is often preferable to work with molality (mol/kg H2O ) rather than amount concentration. In that case, ionic strength is defined as:

m B}=1}^{n} m_{ m B}z_{ m B}^{2}

Importance

The ionic strength plays a central role in the Debye–Hückel theory that describes the strong deviations from ideality typically encountered in ionic solutions. It is also important for the theory of Double Layer (interfacial) and related Electrokinetic phenomena and Electroacoustic phenomena in colloids and other heterogeneous systems. That is, the Debye length, which is the inverse of the Debye parameter ("κ"), is inversely proportional to the square root of the ionic strength. Debye length is characteristic of the Double layer thickness. Increasing the concentration or valence of the counterions compresses the double layer and increases the electrical potential gradient.

Media of high ionic strength are used in stability constant determination in order to minimize changes, during a titration, in the activity quotient of solutes at lower concentrations. Natural waters such as seawater have a non-zero ionic strength due to the presence of dissolved salts which significantly affects their properties.

References

*GoldBookRef|title=ionic strength, "I"|file=I03180

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• ionic strength — joninė jėga statusas T sritis Standartizacija ir metrologija apibrėžtis Jonų sąveikos elektrolito tirpale suminis rodiklis. atitikmenys: angl. ion strength; ionic strength vok. Ionenstärke, f rus. ионная сила, f pranc. force ionique, f …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• ionic strength — joninė jėga statusas T sritis chemija apibrėžtis Jonų sąveikos elektrolito tirpale suminis rodiklis. atitikmenys: angl. ion strength; ionic strength rus. ионная сила …   Chemijos terminų aiškinamasis žodynas

• ionic strength — joninė jėga statusas T sritis fizika atitikmenys: angl. ion strength; ionic strength vok. Ionenstärke, f rus. ионная сила, f pranc. force ionique d’une solution, f …   Fizikos terminų žodynas

• ionic strength — joninis stipris statusas T sritis Standartizacija ir metrologija apibrėžtis Apibrėžtį žr. priede. priedas( ai) Grafinis formatas, Grafinis formatas atitikmenys: angl. ionic strength vok. Ionenstärke, f rus. ионная сила, f pranc. force ionique, f …   Penkiakalbis aiškinamasis metrologijos terminų žodynas

• ionic strength — joninis stipris statusas T sritis fizika atitikmenys: angl. ionic strength vok. Ionenstärke, f rus. ионная сила, f pranc. force ionique, f …   Fizikos terminų žodynas

• ionic strength — a quantity proportional to the amount of electrostatic interaction between ions in solution; equal to where mi is the molar concentration of the medium i, and Zi is the ionic charge. Symbol I …   Medical dictionary

• ionic strength — relating to the mineral requirements in water for supporting the health of fishes residing in that water …   Dictionary of ichthyology

• ionic strength — …   Useful english dictionary

• Total ionic strength adjustment buffer — A Total Ionic Strength Adjustment Buffer ( TISAB ) is a buffer solution which increases the ionic strength of a solution to a relatively high level. This is important for potentiometric measurements, including ion selective electrodes, because… …   Wikipedia

• intermediate; intermittent; internal; internal medicine; intervention; intestine; involvement of a single lymph node [Ann Arbor staging system for Hodgkin disease]; iodine; ionic current; ionic strength; iris; ischemia; isochromosome; isoleucine; isotope; isotropic; nuclear spin quantum number; regi — electric current; incisor [deciduous]; insoluble; isochromosome; optically inactive …   Medical dictionary