The Electromotive Force Method Was Used To Study The Thermodynamic Properties Of RbF/CsF In Aqueous Mixed Electrolyte Solution

The thermodynamic properties of electrolyte solutions were used widely in the salt lake chemistry,environmental protection,metallurgy,biochemistry and so on.Among them,activity coefficient and the related magnitudes can evaluate the ion-ion and ion-solvent interactions,and further reflect the non-ideal behavior of electrolyte solutions.Thus,it is very important to study the thermodynamic properties of electrolyte solutions in theory and practice.Based on the continuous work by our group on Rb and Cs salts,this paper studied the thermodynamic properties of RbF/CsF in the eight mixed electrolyte solution systems by the EMF(electromotive force)method.The galvanic cells without liquid junction were set up with Rb/Cs-ISE and F-ISE(ion selective electrode):(a)Rb/Cs-ISE | A(mA0)| F-ISE(b)Rb/Cs-ISE | A(mA),B(ms)| F-ISEAmong them,electrolyte A is RbF/CsF;electrolyte B is RbCl/CsCl,RbBr/CsBr,RbNO3/CsNO3,Rb2SO4/Cs2SO4.The cells(a)were performed to calculate the Nernst response of the electrode pairs Rb/Cs-ISE and F-ISE at 298.2 K.The results indicated that the electrode pairs had a reasonable Nernst response and can be used for the EMF measurements in this work.The cells(b)were applied for the mixed electrolyte solutions at the ionic strengths ranging from 0.01 to 0.70 mol·kg-1 for different ionic strength fractions of electrolyte B with yB=0.30,0.60,and 0.90,at 298.2 K.The mean ionic activity coefficients of electrolyte A in the different mixed solutions were calculated by the Nernst equation.Then,the experimental data were correlated via the Pitzer model and Hamed model.The Pitzer mixing ionic interaction parameters and Harned empirical parameters of the eight systems have been evaluated.The results show that the eight systems obey the Pitzer model and Harned model.Besides,the mean ionic activity coefficients of electrolyte B,the osmotic coefficients and excess Gibbs free energies of the eight systems,were calculated and discussed in terms of ion-ion and ion-solvent interactions,as well as salt-in and salt-out effects.In addition,the difference of anions and cations in the mixed electrolyte solutions influence on the thermodynamic properties(the mean ionic activity coefficients,the osmotic coefficients and excess Gibbs free energies)was investigated.