Ion Pair Formation of 1-Amidino-O-ethylurea Nickel(II) Chloride and 1-Amidino-O-ethylurea Nickel(II) Bromide in Aqueous Medium at Different Temperatures- A Conductance Method

Abstract

Aqueous solutions of 1-amidino-O-ethylurea nickel(II) chloride and 1-amidino-O-ethylurea nickel(II) bromide have been investigated at different temperatures (303-318 K) by conductance method over wide range of salt concentrations. The limiting equivalent conductances (L₀) and ion association constants (K_A) for various compositions have been calculated using Shedlovsky method. For both electrolytic salts, the limiting equivalent conductances increased linearly with increased in temperature and the ion association constants values increased with rise in temperature. Based on the K_A values and temperature dependence of L_o, the thermodynamic parameters viz., free energy (DGº), enthalpy (DHº) and entropy (DSº) have been determined. The values of L₀ for the electrolytes increase invariably with increase in temperature in aqueous medium, indicating less solvation or higher mobility of ions. This is due to the fact that the increase thermal energy results in bond breaking and leads to higher frequency and higher mobility of the ions. Values of L₀ for [Ni(AEUH)₂]Cl₂ are always greater than those values of complex [Ni(AEUH)₂]Br₂. The values of the K_As for these two complexes increase with rise in temperature. The higher K_A values in case of simple salt compared to complexes salt may be ascribed to the more coulombic type of interaction (specific short-range interaction) between the nickel ion and chloride ion. This is so because the charge density of [Ni(AEUH)₂]Cl₂ is greater than that of the charge density of [Ni(AEUH)₂]Br₂.