According to the recommendations of the IUPAC , the ionic strength can be defined both via the molar concentration and via the molality of the dissolved ions:
Since the ions charge in the square in the ionic strength is received, a doubly charged ion provides four times the contribution to the ionic strength in comparison with a monovalent ion at the same concentration.
In the case of singly charged ions, the ionic strength of completely dissociated electrolytes is equal to the salt concentration. For a saline solution with (NaCl) = 0.001 mol / l, the concentration of the two types of ions Na + and Cl - is also 0.001 mol / l. The ionic strength is due to (Na + ) = 1 and (Cl - ) = −1:
In the case of a 1: 2-valent or 2: 1-valent electrolyte, for example calcium chloride , the ionic strength is three times the salt concentration. For example, for calcium chloride with the charge numbers (Ca 2+ ) = 2 and (Cl - ) = −1 and the stoichiometric ratios (CaCl 2 ) = (Ca 2+ ) = (Cl - ):
Application of the ionic strength I in the Kohlrausch square root equation for the calculation of equivalent conductivities as well as the calculation of activity coefficients of ions in salt solutions; In: Kunze / Schwedt: Fundamentals of qualitative and quantitative analysis, Thieme Verlag Stuttgart, 1996, p. 270 and 47, ISBN 3-13-585804-9
Individual evidence
^ GN Lewis, M. Randall, J. Am. Chem. Soc. , 43, 1921 , 1112.
^ S. Glasstone, An Introduction To Electrochemistry , 2007 , 140.