The solubilities of the metal halides LiF, LiCl, LiBr, LiI, NaF, NaCl, NaBr, NaI, KF, KCl, KBr, KI, RbCl, CsCl,
CsI, were measured at temperatures ranging from 298.15 to 378.15 K in the ionic liquid 1-butyl-3-
methylimidazolium trifluoromethanesulfonate ([C4C1im][OTf]). Li+
, Na+
and K+
salts with anions
matching the ionic liquid have been also investigated to determine how well these cations dissolve in
[C4C1im][OTf]. This study compares the influence of metal cation and halide anion on the solubility of
salts within this ionic liquid. The highest solubility found was for iodide salts and the lowest
solubility, for the three fluoride salts. There is no outstanding difference in the solubility of salts with
matching anions in comparison to halide salts. The experimental data were correlated employing
several phase equilibria models, including ideal mixtures, van’t Hoff, the λh (Buchowski) equation,
the modified Apelblat equation, and the non-random two-liquid model (NRTL). It was found that the
van’t Hoff model gave the best correlation results. On the basis of the experimental data the
thermodynamic dissolution parameters (ΔH, ΔS, and ΔG) were determined for the studied systems
together with computed gas phase metathesis parameters. Dissolution depends on the energy
difference between enthalpies of fusion and dissolution of the solute salt. This demonstrates that
overcoming the lattice energy of the solid matrix is the key to the solubility of inorganic salts in ionic
liquids.