Title: aquamolality
Long Title: IUPAC Gold Book - aquamolality
DOI: 10.1351/goldbook.15314
Status: current

Definition
For a solute \(\ce{B}\) in a system containing solvent \(\ce{A}\) and a reference solvent \(\ce{C}\), \[m_{\ce{B}}^{(\ce{C})} = m_{\ce{B}} \overline M/M_{\ce{C}}\] where \(m_{\ce{B}}\) is the molality of \(\ce{B}\), \(M_{\ce{C}}\) is the molar mass of a reference component, and \(\overline{M}\) is the average molar mass of a mixed solvent, defined for a system containing two solvents as \[\overline M = x_{\nu,\ce{A}} M_{\ce{A}} + (1 - x_{\nu,\ce{A}}) M_{\ce{C}}\] the solvent amount fraction of solvent \(\ce{A}\).

Note
Used most frequently in discussing comparative solubilities in water (\(\ce{C}\)) and heavy water (\(\ce{A}\)) and their mixtures, but applies to any reference component, where solvomolality is a more appropriate term.

Related Term
- amount fraction: https://goldbook.iupac.org//terms/view/15376

Source
- PAC, 2008, 80, 233. 'Glossary of terms related to solubility (IUPAC Recommendations 2008)' on page 239 (https://doi.org/10.1351/pac200880020233)

Other Outputs
- html: https://goldbook.iupac.org/terms/view/15314/html
- json: https://goldbook.iupac.org/terms/view/15314/json
- xml: https://goldbook.iupac.org/terms/view/15314/xml

Citation: Citation: 'aquamolality' 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.15314
License: 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.
Collection: If you are interested in licensing the Gold Book for commercial use, please contact the IUPAC Executive Director at executivedirector@iupac.org .
Disclaimer: 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.
Accessed: 2026-04-21T13:40:54+00:00