Isentropic Compressibility of Aqueous and Methanolic Sodium Thiocyanate Solutions

The speed of sound in aqueous and methanolic sodium thiocyanate solutions was measured as a function of temperature (∼293.15 ≤ T /K ≤ 323.15) and concentration (∼0.0146 ≤ m /(mol kg - 1 ) ≤ 17.328). The isentropic compressibility isotherms for aqueous sodium thiocyanate systems converge at a particular concentration characteristic of the primary hydration shell of the solute. For the methanolic sodium thiocyanate system isentropic compressibility isotherms vary smoothly with concentration. The primary solvation number of the thiocyanate ion has been estimated to be 12.8 in aqueous medium. The total primary solvation number of sodium thiocyanate in methanol medium was found to be 3.7.