Alfred L. M. Bothwell

Standard potentials of the silver–silver chloride electrode in t-butyl alcohol–water mixtures and the thermodynamics of solutions of hydrochloric acid at different temperatures

Electromotive force measurements of cells of the type Pt,H2(g, 1 atm)|HCl(m), ButOH (X),H2O(100 –X)|AgCl-Ag at 5, 15, 25, 35, and 45°C have been used to evaluate (i) the standard potentials of the Ag–AgCl electrode for X= 10, 20, 40, and 70%(w/w) by a polynomial curve-fitting technique, (ii) the mean molal activity coefficients of hydrochloric acid (0·005–0·2 mol kg–1), (iii) the primary medium effects, (iv) the relative partial molal enthalpies, and (v) the thermodynamic functions for the transfer of HCl from water to the respective solvent media. The values of Em° in each solvent have been represented as a function of temperature. The significance of the results has been discussed in relation to the acid–base properties and the breakdown of the structure of water on the addition of t-butyl alcohol.

The activity coefficient and related thermodynamic quantities of HCl in 5 wt-% 1-butanol☆

Abstract Emf measurements of the cells of the type Pt; H 2 (g, 1 atm)/HCl ( m ) in 5 wt-% 1-butanol, AgCl/Ag at five different temperatures ranging from 5–45°C were used to derive (i) the standard potentials of the silver/silver-chloride electrode, (ii) the mean activity coefficients of HCl, (iii) the primary and secondary medium effects, (iv) the relative partial molal enthalpy, and (v) the thermodynamic constants for the process of transfer of HCl from water to 5 wt-% 1-butanol—water. The thermodynamic functions were calculated from the E N ° values and their temperature coefficients for 5 wt-% 1-butanol. The standard emf varied with temperature ( t , °C) according to the equation E m ° = 0·2029 − 7·135 × 10 −4 ( t − 25) − 15·21 × 10 −7 ( t − 25) 2 . The molality of the acid ranged from 0·005 to 0·09 mol/kg. The results are discussed in terms of the acid—base properties and the structure of the solvent.

Thermodynamics of hydrochloric acid in 1-propanol from e.m.f. measurements at 5 to 45 °C

The standard electromotive force of the cell: Pt | H 2 ( g , 1 atm ) | HCI ( m ) in 1 − propanol | AgCI | Ag has been determined at nine temperatures ranging from 5 to 45 °C. The standard e.m.f. E ° varied with Celsius temperature θ according to the equation: E ° / V = − 0.1200 − 15.874 × 10 − 4 ( θ / ° C − 25 ) − 6.529 ( θ / ° C − 25 ) 2 . The activity coefficients of hydrochloric acid, the primary medium effect, and the thermodynamic functions Δ G ° t , Δ H ° t , and Δ S ° t for the transfer of HCl from water to pure 1-propanol have been determined from the e.m.f. measurements. The molality of the acid ranged from 0.006 to 0.099 mol kg −1 . A large positive value for the Gibbs free energy of transfer suggests that the affinity of 1-propanol for HCl is less than that of water. The electrostatic contribution toward the total Gibbs free energy of transfer was evaluated on the basis of Borns electrostatic model and hence the chemical effect has been obtained by subtracting the electrostatic free energy from the total Gibbs free energy. At 25 °C the solvent has a dielectric constant of 20.1.

Thermodynamic properties of hydrochloric acid in dimethylformamide–water mixtures at different temperatures

The standard potential of the Ag–AgCl electrode has been determined from the e.m.f. of a cell of the type Pt,H2(gas 1 atm)|HCL (m), Me2N·CHO (X), H2O (100 –X)|AgCl, Ag at five different temperatures in the range 5–45 °C. Measurements were made in dimethylformamide–water mixtures [X= 5 and 10%(w/w)] for acid concentrations in the range 0·005–0·2 mol kg–1. The mean activity coefficients of HCl have been calculated. The standard thermodynamic quantities (ΔG°, ΔH°, ΔS°, and ΔCp°) accompanying the transfer of HCl from water to the respective solvent media have been computed from the variations of ΔEN°(the difference in standard e.m.f. between the ordinary water and the mixed solvent on the mole-fraction scale) with temperature. The results have been discussed with respect to the solvent structure and acid–base behaviour on the transfer process.

Thermodynamics of hydrochloric acid in propylene carbonate–water mixtures from e.m.f. measurements between 5 and 45 °C

E.m.f. measurements of cells of the type Pt,H2(g, 1 atm)∣HCl(m), PC(X), H2O(100 –X)∣AgCl, Ag at five temperatures from 5 to 45 °C have been used to derive (i) the standard potentials of the Ag–AgCl electrode, (ii) the mean molal activity coefficient of HCl, (iii) the primary medium effects, and (iv) the thermodynamic constants for the transfer of HCl from water to the respective propylene carbonate–water mixtures. The molality of the acid ranged from 0·005 to 0·2 mol kg–1. The standard e.m.f. varied with temperature (t/°C) according to equations (a)–(c) where X=%(W/W) of propylene carbonate. The results of the thermodynamic functions have been interpreted in terms of the acid–base properties and the breakdown of the solvent structure. (a)Em°(X= 5)= 0·2209 – 5·635 × 10–4(t– 25)– 3·293 × 10–6(t– 25)2(b)Em°(X= 10)= 0·2188 – 5·843 × 10–4(t– 25)– 5·165 × 10–6(t– 25)2(c)Em°(X= 20)= 0·2130 – 6·616 × 10–4(t– 25)– 2·725 × 10–7(t– 25)2

Standard potential of the Ag–AgCl electrode and related thermodynamic quantities in butan-1-ol at different temperatures

E.m.f. measurements of cells of the type Pt, H2|HCl(m), BuOH|AgCl–Ag at nine temperatures ranging from 5 to 45 °C were used to derive the standard e.m.f. of the cell in butan-1-ol, the mean activity coefficient of HCl, the primary medium effect, the relative partial molal enthalpy of HCl, and the standard changes of Gibbs energy, enthalpy, entropy, and heat capacity for the transfer of HCl from water to butan-1-ol. These thermodynamic quantities were calculated from ΔE°N and its temperature coefficient. The molality of the acid ranged from 0·005 to 0·15 mol kg–1. The results have been discussed in the light of acid–base properties and the effect of structure of the solvent on the transfer process.

Standard potential of silver-silver chloride electrode and related thermodynamic quantities in glycerol at 5 to 45°C

Summary Standard potentials of the Ag−AgCl electrode in glycerol have been determined by a polynomial curve-fitting program from e.m.f. measurements of cells of the type Pt; H 2 (g, 1 atm) |HCl (m), glycerol| AgCl, Ag, at nine different temperatures in the range 5 to 45°C. The primary medium effect of the solvent upon HCl was also calculated. The temperature variation of the difference in standard e.m.f. in two solvents (water and pure glycerol) was utilized to calculate the thermodynamic quantities (Δ G o , Δ H o , Δ S o , and Δ C p o ) for the transfer of one mole of HCl from water to glycerol. The results have been interpreted in regard to the acid-base properties and the structure of the solvent.

Thermodynamic studies of hydrochloric acid in propan-2-ol from electromotive force measurements between 5 and 45°C

The e.m.f. of the cell Pt, H2(g, 1 atm)| HCl(m), propan-2-ol | AgCl, Ag at 5°C intervals from 5 to 45°C for hydrochloric acid solutions in the range 0.005 to 0.1 mol kg–1 has been used to calculate (a) the standard e.m.f. of the cell at each temperature, (b) the mean molal activity coefficients of HCl at 25°C, (c) the primary medium effet, and (d) the thermodynamic transfer quantities, ΔG°t, ΔH°t, ΔS°t, and ΔC°pt for the transfer of HCl from water to propan-2-ol. The significance of the evaluated thermodynamic functions for the transfer process has been discussed in relation to the acid-base strength, as well as the structural features of the solvents (water and propan-2-ol).

Medium effects and other thermodynamic quantities in 5 wt.% 2-methyl-1-propanol between 5 and 45°C

Summary The standard potentials of the Ag−AgCl electrode in 5 wt.% 2-methyl-1-propanol at five temperatures from 5 to 45°C have been determined by a polynomial curve-fitting technique, using a cell of the type: Pt; H 2 (g, 1 atm) | HCl ( m ) in 5 wt.% 2-methyl-1-propanol | AgCl, Ag. The values can be fitted in the form of equation obtained by using the least squares method: E o m = 0.20350-6.891 x 10 -4 ( t -25) - 17.563 x 10 -6 ( t - 25)These values have been used to derive (a) the activity coefficients of HCl, (b) the relative partial molal enthalpy and heat capacity of HCl, (c) the primary medium effect, and (d) the thermodynamic functions (Δ G o , Δ S o , and Δ H o ) for the transfer of HCl from water to 5 wt.% 2-methyl-1-propanol. The molality of the acid ranged from 0.005 to 0.09 mol kg −1 . The significance of the data has been discussed in terms of the acid-base properties and the structure of water and of mixed solvents on the transfer process.