Solvation Ion Volumes from Solution Densities

Aqueous ion volumes are as useful as they are tricky to quantify. By focusing on the initial slope of solution density versus molarity─an uncommon approach─the partial molar volumes of 48 salts have been reliably quantified, along with uncertainty ranges, and found to be higher than previously reported. Deconvoluting these salt volumes into the volumes of their 24 constituent ions leads to a reliable list of ion volumes in aqueous solution. Specific values (mL/mol) include sodium (4.0 ± 0.2), ammonium (23.2 ± 0.3), nitrate (22.8 ± 0.4), acetate (37.5 ± 0.5), and chloride (12.6 ± 0.2). This work could readily be extended to include even more ions since ultimately it depends on elementary lab technique and careful data analysis.