Dissociation Pressures of Metal Sulfates by Electromotive Force Measurement on SO₂–O₂–SO₃ Concentration Cells with Nasicon Solid Electrolyte

Abstract

Dissociation pressures of nickel, magnesium and copper sulfates have been measured by the electromotive force measurement of the SO₂–O₂–SO₃ concentration cell using NASICON as a solid electrolyte. The standard free energy changes for the dissociation are obtained as follows:

NiSO₄ = NiO + SO₃,

∆G⁰/J mol₋₁ = (2.432 ± 0.024) × 10⁵ − (1.949 ± 0.027) × 10²T (776–1069 K)

MgSO₄ = MgO + SO₃

∆G⁰/J mol₋₁ = (3.033 ± 0.085) × 10⁵ − (1.937 ± 0.085) × 10²T (932–1066K)

and CuO·CuSO₄ = 2CuO + SO₃

∆G⁰/J mol₋₁ = (2.315 ± 0.037) × 10₅ − (1.864 ± 0.040) × 10²T (802–1062 K).

The three-phase coexisting mixture of Cu₂O–CuO–CuO·CuSO₄ is recommended as the solid reference electrode for a potentiometric solid electrolyte SO _x sensor.