Study On The Thermodynamic Properties Of The Ternary System Cesium Bromide + Fatty Alcohol/amide/amino Acid + Water

Thermodynamic properties of electrolytes in mixed solvents were widely used in the electroanalysis corrosion,environmental chemistry,oceanographic geochemistry,industrial chemistry,saline lake chemistry and so on.Among these thermodynamic properties,activity coefficient and osmotic coefficient,excess Gibbs energy and standard Gibbs free energy of transference,are used to evaluate the ion-ion and ion-solvent interactions,and further evaluated the non-ideal behavior of the electrolyte systems.Overall,it is very important to study the thermodynamic properties of the electrolyte in the mixed solvents.Based on the continuous works by our group on rubium and cesium halides,CsBr was selected as electrolyte for its larger radius of anion and cation.The thermodynamic properties of CsBr-alcohol(methanol,ethanol,ethylene glycol,1,2-propylene glycol and glycerol),CsBr-amide(formamide,N,N-dimethylformamide,N,N-dimethylacetamide and urea),and CsBr-amino acid(glycine,L-alanine and L-serine)were determined at 298.15 K.The main research and conclusions are as follows:1.The electromotive force,E,of galvanic cells:Br-ISE | CsBr(m),co-solvents,H2O | Cs-ISE,have been measured firstly at 298.15 K.The values of standard electromotive force,E0,were determined together with extended Debye-Hukel,Pitzer and modified Pitzer.The results show good internal consistency,so the average values for E0*of three models were used to calculate the mean ionic activity coefficients ?± by the Nernst equation.Then,the osmotic coefficient ?,the excess Gibbs free energies GE,the standard Gibbs free energy of transfer ?Gt0,the standard solubility product Ksp,s0 and the primary hydration number nhydr were also evaluated.2.The mean ion activity coefficients ?± decrease with the molality of CsBr for all the ternary systems.It can be explained that the higher concentration of CsBr,the stronger of ion-ion interaction.3.The mean ion activity coefficients ?± of CsBr in different mixed solvents depends on the dielectric constant and structures of the organic solvents.The ?±decreases with the decrease of the dielectric constant of the mixed solvents for alcohols,N,N-dimethylformamide,N,N-dimethylacetamide,the dielectric constants were decreased with the content of the organic solvent increased.This suggest that ion-ion interactions(ion association)is the dominant factor.However,for systems containing formamide,urea and the three selected amino acids,the y± increases with the increase in the dielectric constant of the mixed solvents(increasing in concentration of co-solvent).It can be concluded that the ion-solvent interactions(solvation)are much more important.The dielectric constant are very close,such as the alcohol systems,the activity coefficient mainly affected by structural differences of the organic solvent.4.For the standard Gibbs free energy of transference for CsBr from pure water to the mixed solvent,AGt0 is larger than zero for the systems containing alcohol,N,N-dimethylformamide and N,N-dimethylacetamide,which indicates that the transference process is not spontaneous.But the ?Gt0 is negative for the systems containing formamide,urea and the three selected amino acids,which suggests that the transference process is spontaneous.Moreover,the non-linear relationship between?Gt0 and the content of the organic solvent shows that non-electrostatic interactions also exist in the systems.5.The values of Ksp,s0 and primary hydration number nhydr,for CsBr in the mixed solvents were obtained.These parameters may provide supporting information for the solvation of CsBr in solution.6.The apparent molar volumes V?,limiting partial molar volumes V20,the transfer partial volumes?trV20 and hydration numbers Nh of CsBr in amino acids were calculated at 298.15 K.The V? and V20 of three amino acid in CsBr aqueous solution are positive and increase with increasing the molality of CsBr.It indicate that the interaction between ion and the charged centers of the amino acid in mixed solution was dominated.Moreover,?trV20>0 of the three amino acids in CsBr aqueous solution increased with the increasing of the molality of CsBr.At the fixed molality of amino acids,the order of ?trV20 is:L-serine>glycine>L-alanine.The difference of ?trV20 is mainly from the influence of side chain of amino acid.The hydrophilic-hydrophilic interaction gives a positive contribution to the transfer volume,but the hydrophobic-hydrophobic interactions and vice versa.