Standard potentials of silver–silver bromide electrode in ethylene glycol–water mixtures at different temperatures and related thermodynamic quantities

Abstract

Standard potentials of the Ag–AgBr electrode in ethylene glycol–water mixtures (containing 10, 30, 50, 70, and 90% by weight of glycol) have been determined at 5, 15, 25, 30, 35, and 45°, using a cell of the type: Pt, H₂(gas, 1 atmosphere)|HBr(m), glycol(X), H₂O(Y)| AgBr–Ag

The values of E°_m as a function of the temperature in each solvent can be represented in the form of an equation as shown below: (i) 10% Glycol; E°_m= 0·0676 – 4·85 × 10^–4(t– 25)– 2·92 × 10^–6(t– 25)²(ii) 30% Glycol; E°_m= 0·0585 – 5·27 × 10^–4(t– 25)– 2·50 × 10^–6(t– 25)²(iii) 50% Glycol; E°_m= 0·0480 – 6·59 × 10^–4(t– 25)– 1·64 × 10^–6(t– 25)²(iv) 70% Glycol; E°_m= 0·0328 – 8·65 × 10^–4(t– 25)– 1·21 × 10^–6(t– 25)²(v) 90% Glycol; E°_m=–0·0115 – 1·13 × 10^–3(t– 25)– 9·28 × 10^–7(t– 25)²

The activity coefficients of hydrobromic acid (0·005 – 0·1m) in these media at 5, 25, and 45° have been evaluated. The relative partial molal heat content as well as the medium effect of hydrobromic acid in each solvent has been calculated at 25°. The dependance of the standard electrode potentials on the dielectric constants of the media in the light of the Born equation as well as the volume fraction of water (ϕ_W) in the light of French–Feakins relationship has been examined.