A Thermodynamic Study on the Hydrolysis of Beryllium Ion in Dioxane–Water Mixed Solvents

Abstract

Abstract The hydrolytic reactions of beryllium(II) ions were calorimetrically studied at 25 °C in aqueous solution and dioxane–water mixtures, both containing 3.0 mol dm−3 (Li)ClO4 as a constant ionic medium. On the basis of the formation constants previously determined, the enthalpy and entropy changes for the reaction, qBe2++pH2O=Beq(OH)p(2q−p)++pH+, were estimated for the Be2OH3+ and Be3(OH)33+ complexes in aqueous solution and 0.1 mole fraction dioxane–water mixture and for Be2OH3+, Be3(OH)33+, and Be2(OH)22+ complexes in 0.2 mole fraction dioxane–water mixture. The enthalpy and entropy changes of formation of the Beq(OH)p(2q−p)+ complex obtained in solutions of various mole fractions of dioxane were as follows: 2Be2++H2O=Be2OH3++H+; ΔH12 (mole fraction: 0.0)=18.6±0.2 kJ mol−1, TΔS12(mole fraction: 0.0)=1.3±0.2 kJ mol−1, ΔH12(0.1)=15.2±0.2 kJ mol−1, TΔS12(0.1)=−3.4±0.2 kJ mol−1, ΔH12(0.2)=8.4±0.4 kJ mol−1, TΔS12(0.2)=−12.4±0.4 kJ mol−1, 3Be2++3H2O=Be3(OH)33++3H+; ΔH33(0.0)=61.7±0.2 kJ mol−1, TΔS33(0.0)=12.2±0.2 kJ mol−1, ΔH33(0.1)=59.4±0.2 kJ mol−1, TΔS33(0.1)=10.0±0.2 kJ mol−1, ΔH33(0.2)=59.0±0.4 kJ mol−1, TΔS33-(0.2)=9.1±0.4 kJ mol−1, 2Be2++2H2O=Be2(OH)22++2H+; ΔH22(0.2)=42.3±0.4 kJ mol−1, TΔS22(0.2)=1.3±0.4 kJ mol−1. The enthalpy and entropy changes of the reaction, H2O=H++OH−, in the solutions of the same compositions were also determined as ΔHw(0.0)=56.6±0.1 kJ mol−1, TΔSw(0.0)=−22.6±0.1 kJ mol−1, ΔHw(0.1)=58.1±0.1 kJ mol−1, TΔSw(0.1)=−25.3±0.1 kJ mol−1, ΔHw(0.2)=61.2±0.1 kJ mol−1, TΔSw(0.2)=−26.6±0.1 kJ mol−1. These results were discussed in connection with interactions between the hydroxo complexes and the solvent molecules and with those between solvent molecules in the mixed solvents.