Use the calculator to find concentration from moles and solution volume (Direct Molarity tab). For a specific ion produced by a dissolved salt, use the From Compound tab (assumes complete dissociation and anhydrous formulas). The dilution tab applies the standard dilution relationship C1V1 = C2V2.

Ionic Concentration Calculator

From a Salt
Dilute a Solution

Pick the salt, enter the mass dissolved and the solution volume.

Ionic Concentration (for a specified ion) Formula

The following formula is used to calculate the concentration of a specified ion (or any other specified dissolved species) in a solution.

C_i = n_i / V

Variables:

  • Ci is the molar concentration of the specified ion/species i (mol/L)
  • ni is the amount (in moles) of that ion/species i present in the solution (mol)
  • V is the volume of the solution (L)

To calculate an ion’s concentration, divide the moles of that ion (ni) by the solution volume (V). If you start from a fully dissociated ionic compound, the moles of a given ion are found from the compound amount using stoichiometry (for example, 1 mol CaCl2 produces 1 mol Ca2+ and 2 mol Cl−). For weak electrolytes, dissociation may be incomplete, so ion concentrations can be lower than stoichiometric estimates.

What is an Ionic Concentration?

Ionic concentration refers to the amount (typically in moles) of a specified ion in a given volume of solution (for example, [Na+] or [Cl−]). Ions are atoms or molecules that have lost or gained electrons, resulting in a positive or negative charge. Concentration is commonly reported in moles per liter (mol/L), meaning “moles of that specified ion per liter of solution.” For ionic compounds, the ion concentration depends on how many ions each formula unit produces and how completely the compound dissociates in the solvent.

How to Calculate Ionic Concentration?

The following steps outline how to calculate the Ionic Concentration using the formula Ci = ni / V.

  1. First, determine the amount of the ion/species of interest (ni) in moles (using dissociation stoichiometry if starting from a compound).
  2. Next, determine the volume of the solution (V) in liters.
  3. Next, gather the formula from above: Ci = ni / V.
  4. Finally, calculate the concentration in mol/L.
  5. After inserting the values of ni and V into the formula and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

amount of compound = 0.5 mol NaCl (assume complete dissociation)

volume of the solution (V) = 0.2 L