Koeficijenti aktivnosti u trokomponentnim vodenim rastvorima elektrolita sa zahedničkim kalijum jonom na T=298,15 K

Abstract

Predmet ovog rada je proučavanje termodinamičkih osobina trokomponentnih vodenih rastvora elektrolita sa zajedničkim kalijumovim jonom: {yKCl+(1-y)K2HPO4}(aq), {yKNO3+(1-y)K2HPO4}(aq), {yKBr+(1-y)K2HPO4}(aq) na temperaturi 298.15 K. Primenom izopiestičke metode određeni su osmotski koeficijenti u navedenim sistemima kao i rastvorljivost K2HPO4 u sistemu K2HPO4(aq) na temperaturi 298.15 K. Obrada eksperimentalnih rezultata za čiste rastvore elektrolita K2HPO4(aq), KNO3(aq) i KBr(aq) izvedena je proširenim modelom Pitzer-a i modelom Clegg-a. Oba modela daju zadovljavajuće rezultate fitovanja eksperimentalnih podataka i standardnu devijaciju reda veličine 10–3. Na osnovu izopiestičkih rezultata utvrđeno je da molalnost zasićenog rastvora K2HPO4(aq) na temperaturi 298,15 K u ravnoteži sa K2HPO4∙xH2O(cr) iznosi msat=10.6 mol∙kg–1 a u ravnoteži sa K2HPO4∙3H2O(cr) iznosi msat= 9.7429±0.0023 mol⋅kg-1. Obrada eksperimentalnih rezultata mešanih rastvora elektrolita izvedena je modelima: Scatchard–a, Pitzer-a i Clegg-a, pri čemu je u modelima Pitzer–a i Clegg-a razmatran i uticaj elektrostatičkih članova višeg reda. Primena članova ne daje znatno bolje rezultate fitovanja. Sva tri modela daju zadovoljavajuće rezultate fitovanja osmotskih koeficijenata u ispitivanim sistemima a standardna devijacija je reda veličine 10-3.. Model Scathard–a sa šest parametara mešanja daje najbolje slaganje eksperimentalnih i proračunatih vrednosti osmotskih koeficijenata. Vrednosti koeficijenta aktivnosti K2HPO4 u sva tri sistema opadaju sa porastom jonske jačine sistema i rastu sa porastom udela jonske jačine drugog elektrolita u sistemima {yKCl+(1-y)K2HPO4}(aq), {yKBr+(1-y)K2HPO4}(aq) a opadaju u sistemu {yKNO3+(1-y)K2HPO4}(aq). Vrednosti koeficijenta aktivnosti KCl i KBr opadaju sa porastom jonske jačine do I ≈4 mol∙kg–1 a rastu sa porastom udela jonske jačine KCl i KBr. U sistemu {yKNO3+(1-y)K2HPO4}(aq) koeficijent aktivnosti KNO3 opada sa porastom jonske jačine i udela jonske jačine KNO3...

The object of this work is the study of thermodynamic properties of ternary aqueous solutions of electrolytes with common, potassium cation: {yKCl+(1-y)K2HPO4}(aq), {yKNO3+(1-y)K2HPO4}(aq), {yKBr+(1-y)K2HPO4}(aq) at temperature 298.15 K. Isopiestic method was used for determination of osmotic coefficients of former ternary systems as well as for solubility of K2HPO4 in the system K2HPO4(aq) at temperature 298.15 K. Treatment of experimental data of binary aqueous solutions of electrolytes K2HPO4(aq), KNO3(aq) and KBr(aq) is performed by the Extended Pitzer model and Clegg’s model. Both models are giving satisfying results of fitting the experimental data with standard deviation of fit being of the order 10–3. On the bases of isopiestic results it is determined that the molality of saturated solution K2HPO4(aq) at temperature 298,15 K in equilibrium with solid phase K2HPO4∙xH2O(cr) is msat=10.6 mol∙kg–1. and in equilibrium with K2HPO4∙3H2O(cr) is msat= 9.7429±0.0023 mol⋅kg-1. Treatment of experimental results of ternary aqueous solutions of electrolyte was perfomed using the Scatchard, Pitzer and Clegg models where in last two models the influence of higher order electrostatic terms was taken into account. These higher order electrostatic terms didn’t give much of improvement in fitting the results. All three models gave standard deviation of fitting osmotic coefficients of the order 10-3. The Scatchard model with six mixing parameters gave the best agreement between experimental and calculated osmotic coefficients values for all the investigated systems. Values of activity coefficient of K2HPO4 in all three systems decrease with increasing total ionic strength of the system and with higher ionic strength fraction of other electrolyte show increasment in the systems {yKCl+(1-y)K2HPO4}(aq), {yKBr+(1-y)K2HPO4}(aq) and decreasment in the system {yKNO3+(1-y)K2HPO4}(aq). Values of activity coefficient of KCl and KBr decrease with increasing total ionic strength of the system up to I ≈4 mol∙kg–1 but increase with higher ionic strength fraction of KCl and KBr. In the solution {yKNO3+(1-y)K2HPO4}(aq) mean ionic activity coefficient of KNO3 is lowering with the increase of both total ionic strength and ionic strength fraction of KNO3...