Détermination par voie électrochimique des propriétés acido-basiques et oxydo-réductrices des solutions concentrées en acide phosphorique progressivement neutralisées par la soude

Abstract

Acid–base properties in 7 M H3PO4 medium neutralized by soda are characterized with an R(H) acidity function and R(H2PO4−), R(HPO42−), R(PO43−) basicity functions, which respectively represent the H+ activity in these media and their ability to donate H2PO4−, HPO42−, PO43− ions. The acidity level of these media (Na/P = 0.0–1.6), changes from R(H) = −2.7 to R(H) = +7.5. The accessible potential domain for the media studied is close to 1.23 V. Activities of these solutions in water vary between 0.66 and 0.81. The ranges of electroactivity for platinum, carbon, and mercury electrodes are also determined.

Electrochemistry in Concentrated Hydrochloric Acid (C ≤ 5 M) Progressively Neutralized by Sodium Hydroxide Pellets: Acid−Base, Oxidation−Reduction, and Solvation Properties of the Medium

“… One can notice that the acidity level is lowered up to 2.5 units when the ratio Na/H is raised from 0.0 to 1.0. Of course, this is essentially due to the addition of sodium hydroxide pellets, although Bessiere et al assigned part of this decrease to the water that originates from the neutralization process itself.

1 Variation of the Ro(H) function in 5 M hydrochloric acid progressively neutralized by sodium hydroxide.

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“…Generally, the potential of the Q/QH 2 system in concentrated media is obtained by the carbon paste electrode technique. This is the case for the concentrated phosphoric media, 6,9,[11][12] for which the zero current potential obtained with a carbon paste electrode that comprises both chloranil and hydrochloranil (Q, QH 2 ) is well defined and perfectly stable. By contrast, in the present work, a different behavior is observed with the neutralized HCl.…”

“…Concentrated media with various compositions have been the subject of experiments so far, and it appears that salt solutions of various acidity levels are among the most convenient . As a matter of fact, concentrated chloride media are often used in hydrometallurgy either in their hydrogen form or in their alkaline-earth form.…”

“…Concentrated media with various compositions have been the subject of experiments so far, and it appears that salt solutions of various acidity levels are among the most convenient. 6 As a matter of fact, concentrated chloride media are often used in hydrometallurgy either in their hydrogen form or in their alkaline-earth form. The knowledge of their chemical properties in view of a better understanding of the behavior of solutes thus appears as a matter of crucial scientific interest.…”