Ionic Strength Calculator

Your details

Manual lets you specify up to five individual ions. Salt preset handles complete dissociation automatically for common salts.
Molarity (mol/L) is most common for aqueous solutions. Molality (mol/kg of solvent) is preferred for temperature-sensitive work. The ionic strength formula structure is identical for both.
Molar or molal concentration of ion 1.
mol/L
Signed charge number. Use +1 for Na+, -1 for Cl-, +2 for Ca2+, -2 for SO4 2-, etc.
Leave blank to use only ions 1 and above.
mol/L
Signed charge number for ion 2.
Optional third ion.
mol/L
Signed charge number for ion 3.
Optional fourth ion.
mol/L
Signed charge number for ion 4.
Optional fifth ion.
mol/L
Signed charge number for ion 5.
Ionic strengthModerate
0.15mol/L

I = 0.5 * sum(c_i * z_i^2)

Activity coeff. (z = 1)0.6351
Activity coeff. (z = 2)0.1627
Activity coeff. (z = 3)0.0168
0.15 mol/L
Very dilute<0.01Dilute0.01-0.1Moderate0.1-0.5High0.5+

Ionic strength: 0.1500 mol/L

  • The ionic strength is 0.1500 mol/L. At this level, inter-ionic interactions are significant and the Debye-Huckel limiting law may underestimate deviations from ideality.
  • Mean activity coefficient for monovalent ions (z = 1): 0.6351. For divalent ions (z = 2): 0.1627. Higher-charge ions deviate more from ideal behaviour because the Debye-Huckel exponent scales with z squared.

Next stepUse the activity coefficients above to convert measured concentrations to thermodynamic activities when calculating equilibrium constants, solubility products, or electrode potentials.

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