semisodium

Semisodium is a historical or nonstandard term that has been used to describe a salt in which only part of the acidic protons of an acid has been replaced by sodium ions. In such a salt, sodium is present alongside remaining hydrogen-bearing groups, resulting in a compound with both sodium ions and protonated components. The term is not part of modern IUPAC nomenclature and its precise meaning can be ambiguous.

In current chemical practice, such species are usually described by explicit formulas or by standard names that indicate the degree of neutralization, such as monosodium salt, disodium salt, or mixed salts with defined stoichiometry. Because semisodium lacks a universally fixed structure, its usage can lead to confusion about composition, charge balance, and properties.

In solution, semisodium formulations, if they are mixtures rather than discrete well-defined compounds, may equilibrate with other protonation states of the anion depending on pH and counterions. Consequently, the observed properties—solubility, acidity, and reactivity—often reflect a distribution of species rather than a single, well-defined compound.

Overall, semisodium is rarely used in modern chemistry. When encountered, it is advisable to refer to the exact chemical formula or to the specific nomenclature that conveys the intended degree of neutralization, such as the monosodium, disodium, or other clearly defined salt. See also monosodium salt, disodium salt, mixed salt, and salt nomenclature.