= Ionic strength
{title2=$I_c=\frac12\sum_i c_i z_i^2$}
{wiki}
The concentration-based <ionic strength> is $I_c=\frac12\sum_i c_i z_i^2$, where $c_i$ is each dissolved <ion>'s <concentration> and $z_i$ its signed <electric charge> number. It has the same units as $c_i$; some formulas instead use the <dimensionless> ratio $I_c/c^\circ$. All dissolved <ions> contribute, including those that balance the <electric charge> of a <buffer solution>'s <conjugate base>. <Ionic strength> helps describe the interactions represented by <activity coefficients>. See https://eprints.whiterose.ac.uk/id/eprint/167121/1/BM_5_2020_Unterricht_Hippler_Metcalfe.pdf[Hippler and Metcalfe, activity coefficients and dimensionless ionic strength].
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