Ionic Strength Calculator
Sum the concentration weighted charge squared terms to estimate ionic strength for electrolyte solutions.
Ionic strength
0.1 mol/L
How to Use This Calculator
List every ion
Add each ionic species in the solution, including counter ions and spectator ions.
Enter concentrations
Use molar concentrations (mol per liter). For ionic strength, molality can often be substituted for dilute solutions.
Provide ionic charges
Charges may be positive or negative. The calculator squares them automatically.
Interpret the result
Ionic strength controls activity coefficients and screening lengths in electrolyte theory.
Formula
I = 0.5 sum(ci zi2)
Sum over all ions where ci is concentration (mol/L) and zi is the ionic charge. Multiply by 0.5 to avoid double counting interactions.
Example
A 0.1 M NaCl solution has I = 0.5[(0.1)(12) + (0.1)(-12)] = 0.1 mol/L. A 0.05 M CaCl2 solution gives I = 0.5[(0.05)(22) + 2(0.05)(12)] = 0.15 mol/L.
Full Description
Ionic strength measures the electrostatic environment created by dissolved ions. Higher values compress the electrical double layer and reduce activity coefficients.
Useful in equilibrium, kinetics, and electrochemistry, ionic strength helps correct concentrations to activities using Debye-Huckel or extended models.
Frequently Asked Questions
Do neutral species contribute?
No. Only ions with nonzero charge affect ionic strength.
Can I use molality instead?
For dilute aqueous solutions, molarity and molality are similar. Use molality for more concentrated or non-aqueous systems.
What about multivalent ions?
Multiply the concentration by the square of the charge. High valence ions quickly increase ionic strength.
How does ionic strength impact equilibrium constants?
Activity coefficients change with ionic strength, modifying the effective equilibrium constant. Correct by using activity-based constants.
Do I need to consider temperature?
Ionic strength itself does not include temperature, but activity coefficient models that use it often depend on temperature.