Ionic Strength Calculator - Free Online Tool

Calculate your ionic strength with our free online tool.

Get accurate results instantly.

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How This Tool Works

The ionic strength (I) measures the total concentration of ions in a solution, weighted by ion charge. This calculator uses the standard relationship I = 1/2 x Σ(cizi2).

Enter each ion's molar concentration and charge magnitude. The tool squares each charge, multiplies by concentration, applies the 1/2 factor, and sums the ion contributions.

  • Input: Ion name, concentration in mol/L, and charge magnitude.
  • Output: Ionic strength in mol/L plus each ion's contribution.
  • Example: 0.1 M NaCl contributes 0.05 from Na+ and 0.05 from Cl-, for an ionic strength of 0.1 mol/L.

Why This Matters in Chemistry

Ionic strength affects activity coefficients, solubility, electrochemical measurements, reaction equilibria, and buffer behavior. Solutions with the same molarity can behave differently when multivalent ions are present because charge is squared in the formula.

Use mol/L consistently for each ion concentration, and split salts into their dissolved ions before entering values.

Common Mistakes to Avoid

  • Do not enter the salt only: NaCl should be entered as Na+ and Cl-.
  • Account for stoichiometry: 0.1 M CaCl2 produces 0.1 M Ca2+ and 0.2 M Cl-.
  • Keep concentrations positive: Charge sign does not change the result because the charge is squared.

Frequently Asked Questions

Common questions about the Ionic Strength Calculator - Free Online Tool

Concentration describes how much of a substance is present in a mixture. It can be expressed as mass/volume (mg/L), molar (mol/L), parts per million (ppm), or percentage.
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Sources & References

International System of Units (SI): amount-of-substance concentration

Amount-of-substance concentration is measured in the mole per cubic metre (mol/m³). Conversions between SI and other units use exact, internationally agreed factors maintained by NIST.
→Source: NIST — International System of Units (SI)

International System of Units (SI)

Authoritative definitions for amount-of-substance concentration, from the BIPM SI Brochure (9th edition), the defining reference for the SI.
→Source: BIPM — SI Brochure (9th ed.)

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