Compute ionic strength from the molality and charge of one or two ions.
| Ionic strength I | – |
Use this calculator when preparing a buffer or a Debye–Hückel estimate: you know the salt recipe and need I before looking up an activity coefficient.
The calculation is I = ½ (m₁z₁² + m₂z₂²). For 0.10 mol/kg NaCl, enter m1 = 0.10, z1 = 1 and m2 = 0.10, z2 = 1 (cation and anion). Leave the second ion at 0 if you only have one species. Charge is squared, so the sign of z does not matter; type 2 for sulfate, not −2.
This is the two-ion form of the definition. Extra ions are omitted unless you fold them into one of the two slots.
m1: Molality (or molarity in dilute water) of the first ion, mol/kg or mol/L.
z1: Charge number of that ion. 1 for Na⁺, 2 for SO₄²⁻.
m2: Molality of a second ion, or 0 if you enter only one species.
z2: Charge number of the second ion. Ignored if m2 is 0.
Ionic strength I: I in the same concentration unit as m, typically mol/kg.
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