✍ Scribed by A.M.Shams El Din; A.A.A. Gerges
No coin nor oath required. For personal study only.
The feasibility of the Cu/CuO electrode for O*--ion determination and for acid-base titrations in molten KNO, at 350°C has been established. The potential of the electrode varies linearly with log [0*-l and the slope of the calibration curve is 2.303(RT/2F) at the working temperature. This allows the determination of the Cu/CuO/OB-standard potential. The CuO electrode is used for titrating the acid K&,0, with NasOII in molten KNO,. Sharp potential drops are recorded at the equivalence points. The equilibrium constant of the reaction CrBO,e-+ O*-= 2CrO,"-is calculated as cu l-8 x lo'*. The standard O.JO*-potential in fused KN08 at 350°C has been calculated indirectly. With this value and the potentiometric titration curves obtained with the oxygen electrode, the first known acid-base equilibrium constants in fused salts are computed, as follows: 2P09-+ OS-= P*0,4-, K = 3.1 x 1016 2HaP0,-+ 02-= 2HP0,2-+ HeO, K = 3.9 x lOI V*O,'-+ 02-= 2vo,*-, K = 4.5 x 108 P,O,"-+ OS-= 2POaS-, K = 6.6 x IO6 2HP0,a-+ Oa-= 2P04'-_t HaO, K = 2.8 x lo6 2HAs0,2-+ O*-= ~AsO,~-+ HeO, K = 2,6 x lop. A correlation is drawn between the equilibrium constants calculated in the present study and the acidity numbers of the same oxy-anions previously proposed. R&um&L'on Ctablit que l'electrode Cu/CuO convient a la determination de [Oe-] et aux titrages acide-base en KNO, fondu a 350°C. La tension reversible varie lineairement avec log [0*-J, avec une pente 2,303(RT/2F), ce qui permet le calcul de la tension standard Cu/CuO/O*-. Application au titrage de K&&O, par Na,O en KNOI fondu; des pentes abruptes sont obtenues aux points d'equivalence; on en d&luit la constante 1,8 . lOI* de l%quilibre CrBO,a-+ Oa-e 2Cr0,a-. .On peut aussi obtenir indirectement la tension standard OJO*-a 350°C en KNOJ fondu et les courbes de titrages avec electrode a oxygene permettent d&s lors de calculer les constantes de equilibres 2POa-+ O*-z P,O,'-; 2H,PO,-+ 02-e 2HPOa2-+ HzO; v,o,*-+ o*-* 2v015-; P*o,4-+ o*-* 2POaS-; 2HPOa2-+ 02-s 2POls-+ H*O; 2HAsOaZ-+ 02-e 2AsO,+ + H,O. 11 existe une correlation entre ces constantes d'bquilibre et des "nombres d'aciditt" prtidemment proposes. ZusammenfassunS-Die Eignung von Cu/CuO-Elektroden zur O*--1onenBestimmung und fiir S&m-Basen-Titrationen in geschmolzenem KNOIl bei 350°C wurde untersucht. Das Potential der Elektrode iindert sich linear mit log [0*-J und die Steigung der Eichkurve betragt genau 2,303(RT/2F) bei der Arbeitstemperatur. Diese Tatsache ermoglicht die Bestimmung des Cu/CuO/O*-Standardpotentials.
Die CuO-Elektrode wird verwendet zur Titration der S&.ue K
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