15335 IUPAC Gold Book - ionic mole fraction 10.1351/goldbook.15335 15335 current synonyms: ionic amount fraction, species amount fraction, species mole fraction 1 For an ionized salt \(\ce{B}\) in solution, \[x_{+\rm{B}} = \frac{\nu_{+\ce{B}}x_{\ce{B}}}{1 + \sum \limits_{i=1}^{s} \left(\nu_{i} - 1 \right)x_{i}},x_{-\ce{B}} = \frac{\nu_{-\ce{B}}x_{+\ce{B}}}{\nu_{+\ce{B}}}\] where the summation is over all $s$ solute components \(i\) and \(\nu_{i} = \nu_{+i} + \nu_{-i}\) is the sum of the stoichiometric numbers of the ions formed from salt \(i\). For a single solvent \(\ce{A}\) in an ionic solution, \[x'_{\ce{A}} = \frac{x_{\ce{A}}}{1 + \sum \limits_{i=1}^{s} \left(\nu_{i} - 1 \right)x_{i}}\] Note 1: These are generalizations of terms and are used in formulating fitting equations for solubility of salts, in defining activity coefficients on the mole fraction scale, and in discussing salt effects on solubilities of gases.Note 2: Note that \[\sum \limits_{i=1}^{s} \left(x_{+i} - x_{-i} \right) + x'_{\ce{A}} = 1\] components https://goldbook.iupac.org//terms/view/16268 mole fraction https://goldbook.iupac.org//terms/view/15376 PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 250 (https://doi.org/10.1351/pac200880020233) https://goldbook.iupac.org/terms/view/15335/html https://goldbook.iupac.org/terms/view/15335/json https://goldbook.iupac.org/terms/view/15335/plain Citation: 'ionic mole fraction' in IUPAC Compendium of Chemical Terminology, 5th ed. International Union of Pure and Applied Chemistry; 2025. Online version 5.0.0, 2025. 10.1351/goldbook.15335 The IUPAC Gold Book is licensed under Creative Commons Attribution-ShareAlike CC BY-SA 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) for individual terms. If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org . The International Union of Pure and Applied Chemistry (IUPAC) is continuously reviewing and, where needed, updating terms in the Compendium of Chemical Terminology (the IUPAC Gold Book). Users of these terms are encouraged to include the version of a term with its use and to check regularly for updates to term definitions that you are using. 2026-04-21T01:39:36+00:00