Determination Of Thermodynamic Properties Of Systems MCl-Alcohol-H₂O (M=Rb, Cs) By Electromotive Force Measurements

It is well known that the rubidium, cesium and their salts are rare all over the world. They can not form any minerals of their own because of the extremely reactivity. The market for them is very small, and the price is high. There are less thermodynamic property data for the two metals and their salts than other alkali metals and the related compounds. Actually, some studies on rubidium and cesium show us that both metals and their salts have many uses, such as specialty glasses used in fiber optic telecommunication systems, night-vision equipment, and an ingredient of metal-ion catalysts and so on. For our work, it is useful to provide the related thermodynamic property data with all alkali salts system; to develop electrolyte solution theories. What's more, we eager to apply such researches to develop the corresponding industry, medical science and other areas.This experimental work mainly includes two parts:In the one part, determination of thermodynamic properties of systems by electromotive force measurements, we have combined the rubidium or cesium ion selective electrode and Ag|AgCl electrode to establish galvanic cells:Rb-ISE|RbCl(m), alcohol(Y), H₂O(100-Y)|Ag|AgClCs-ISE|CsCl(m), alcohol(Y), H₂O(100-Y)|Ag|AgClHere, m was the molality of RbCl or CsCl in solvent; Y was the mass fraction percent of alcohol. The emf readings were carried out at the different molalities of RbCl or CsCl in the methanol/ethanol-water mixtures at 298.15 K, in the range 0-40% (Wt.%) alchohol and in the methanol-water mixtures at 308.15 K, in the range 0-40% (Wt.%) methanol. While the Pitzer model was adopted to describe the behavior of electrolyte; the activity coefficients, E⁰ and the related model parameters were calculated in different ratios of alcohol-water mixtures. The Pitzer-Simonson-Clegg model was also applied to correlate the data of RbCl or CsCl in the methanol-water systems at 298.15 K and 308.15 K. It is found that the Pitzer model and the Pitzer-Simonson-Clegg model are both satisfactory for our work.On the foundation of the models, the osmotic coefficients, the medium effects and the free energies of transfer of rubidium chloride or cesium chloride from water to alcohol-water mixtures were calculated. Moreover, the densities and the refractive indices of every system were determined as well.The other part is solubility prediction. We have made a prediction of solubility of CsCl in system CsCl-MeOH-H₂O at 298.15 K on the basis of Pitzer model and free energies minimum measurement. The result showed that this measurement of solubility prediction was satisfactory for system MCl-MeOH-H₂O. This is the significant research on the solubility prediction for electrolyte in alcohol-water mixtures. It could be said that our work laid the foundation of the future work about this area and was of profound theoretical and practical significance.