Use this formula to calculate ionic strength: I= 1/2 n∑i (CiZi )squared, where "I" represents ionic strength, "n" represents the number of ions in solution, "i" represents the specific ion in solution, "Ci" represents the concentration to the /th species, such as moles per liter, "Zi" represents the valence or oxidation number of the /th species and "∑" represents the summation of concentrations and valences of all ions. Remember positive and negative ions cannot separate, which needs to be considered as a factor in the equation.

For example, say you want to find the ionic strength of 1.0 M La2(SO4) plus 1.0 M CaCl2.

List the concentrations. For example, La 3+= 2.0 M, SO4 2- =3.0 M, Ca2 1+= 1.0 M, Cl 1- = 2.0 M.

Input concentrations and valences into the Debye and Huckel equation.

I = ½(2_3(Squared)+3_2(Squared)+1_2(Squared)+2_1(Squared)).

Calculate for result, understanding that the formula is the molar concentration of the ion multiplied by the valence squared. Take {2*32} in the formula above for example. The 2 is the molar concentration of La (Lanthanum), the 3 is the valence of electrons of La, and the valence is squared. The ionic strength is 18.0.