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Thermodynamic and related studies of aqueous copper(II) sulfate solutions

Akilan, Chandrika (2008) Thermodynamic and related studies of aqueous copper(II) sulfate solutions. PhD thesis, Murdoch University.

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This thesis describes a systematic investigation of the thermodynamic quantities associated with the interaction between Cu2+ and SO42- in aqueous solution. A variety of techniques including UV-Visible spectrophotometry, Cu(II) ion-selective electrode potentiometry, dielectric relaxation spectroscopy and titration calorimetry have been used.

The values for the (aq) association constants determined by UV-Vis spectrophotometry in NaClO4 media as a function of ionic strength were in good agreement with published data but were lower than the values obtained from Cu(II) ion -selective electrode potentiometry. The source of this difference was traced to the presence of solvent-separated ion pairs which are only partially detected by UV-Vis spectrophotometry. This was shown by a detailed investigation of CuSO4(aq) over a wide range of concentrations using modern broad-band dielectric relaxation spectroscopy (DRS). This technique revealed the presence of three ion-pair types: double solvent-separated, solvent-shared and contact ion pairs.

Calorimetric titrations using the log KA values determined by potentiometry, have provided for the first time reliable values for the enthalpy and entropy changes associated with complex formation between Cu2+(aq) and SO42-(aq) system over range of ionic strengths (in NaClO4 media). These data were fitted to a specific ion interaction model to obtain the standard state value which was in excellent agreement with the values obtained in other studies and from the DRS work in this study.

In addition, investigations have been carried out into the physicochemical properties, (osmotic coefficients, densities, heat capacities, solubilities and viscosities) of ternary mixtures of CuSO4(aq) with Na2SO4(aq) or MgSO4(aq). The isopiestic measurements (water activities) of the mixtures were in general well described by Zdanovskii's rule, especially for the mixtures of CuSO4 with MgSO4. The densities of the ternary mixtures of CuSO4 with MgSO4 were found to follow Young's rule of mixing but those of CuSO4 with Na2SO4 deviated from linearity. The solubilities of the salts in their ternary mixtures agree well with literature data and show that the solubility of MgSO4 or CuSO4 decreases with increasing Na2SO4 concentration. The viscosities of all the ternary mixtures show clear negative departures from 'Young's rule' type behaviour.

Item Type: Thesis (PhD)
Murdoch Affiliation: School of Chemical and Mathematical Science
Supervisor(s): Hefter, Glenn and May, Peter
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