samarium chloride: activity coefficients
Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Abstract A comprehensive array of electrochemical cell measurements for the system HCl +SmCl3 + H2O was made from 5 to 55°C using a cell without liquid junction ofthe type:Pt; H2(g, 1 atm)|HCl (m A) + SmCl3 (m B)|AgCl, Ag (A)The present study, unlike previous studies of trivalent ions, are not complicatedby hydrolysis reactions. Measurements of the emf were performed for solutionsat constant total ionic strengths of 0.025, 0.05, 0.1, 0.25, 0.5, 1.0, 1.5, 2.0, 2.5,and 3.0 mol-kg−1. The mean activity coefficients of HCl (γHCl) in the mixtureswere calculated using the Nernst equation. All the experimental emf measurements(about 850) were first treated in terms of the simpler Harned's rule. Harnedinteraction coefficients (αAB and βAB) were calculated. The linear form of Harned'srule is valid for most ionic strengths, but quadratic terms are needed at I = 1.5and 3 mol-kg−1. The Pitzer model was used to evaluate the activity coefficientsusing literature values, β(0), β(1), and C φ, for HCl from 0 to 50°C and 25°C forSmCl3. The effect of temperature on the parameters for SmCl3 has been estimatedusing enthalpy and heat-capacity data. The mixing parameter ΘH,Sm wasdetermined at 25°C. The addition of the ΨH,Sm,Cl coefficient did not improve the fitsignificantly and no temperature dependence was found to be significant. Thevalue of ΘH,Sm = 0.2 ± 0.01 represented the values of γHCl with a standarddeviation of σ = 0.009 over the entire range of temperatures and ionic strength.The use of higher-order electrostatic effects (EΘH,Sm, EΘH,Sm) was included as itgave a better fit of the activity coefficients of HCl.
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