Notizen: Electrometric Studies on the Compositions of Uranyl Isopolytungstates

Abstract

Todate, available literature, furnishes no informa tion regarding the application of electrometric methods, to study the nature and compositions of the compound formed by the interaction of uranyl nitrate and various tungstate isopolyanions. Much earlier L e f o r t x, ob tained uranyl compounds of the compositions U02 -W04 and U02W04 • 2 W035 H20 etc. by analytical means. His results, however, could not be confirmed by later workers.There is a great difficulty in assigning a definite composition to such a metallic tungstate precipitated by analytical methods, because of the presence of con stitutionally bounded water molecules and hydration of the products, as well as the possibility of formation of double compounds, coprecipatation and occlusion. Analytical results alone fail, therefore, to give a true picture of the polysalt thus formed.Owing to lade of any specific and sensitive electrometric method, the present work was initiated with a view to study the reaction equilibria between uranyl nitrate U02 (N03) 2 and various isopolytungstate by amperometric, pH and conductometric methods of titra tions. The results are being incorporated in the present paper in-continuation of our earlier similar investiga tions 2' 3. Experimental AnalaR (B.D.H.) U02 (N03) 2 -6H20, Na2W04 -2H20, NaC104 and gelatine were used. Air free conductivity water was used for preparation and subsequent dilu tions of the solutions.A manual polarograph with a scalamp galvanometer, was used for entire polarographic and amperometric work. Polarographic behaviour of 1 mm U022® was studied in 0.1 m NaC104 as supporting electrolyte and 0.001% gelatine as maxima supressor. A dropping mer cury electrode with characteristics m2,3tlj6 = 2.52 mg2/s sec~1/2 was used in conjunction with a saturaded calo mel electrode connected through a salt bridge. A reduc tion potential of -1.00 V (vs S.C.E.) was applied for all amperometric titrations, which is beyond the limiting current plateau of the second step of the wave. The first step limiting current plateau was also tried but was found to be unsuitable. The procedure adopted in entire amperometric work is the same as described in our earlier communications 3' 4.The various alkalituungstate solutions were prepared by addition of requisite amounts of A.R. HC1 to standard normal Na2W04 solution at 100 °C. A series of ampero metric titrations were performed using 0.1 m NaC104 as Supporting electrolyte and 0.001% gelatine as a maxima suppressor. pH titrations were carried out with the help of a Cambridge null deflection type pH meter using a glass electrode of 0 -1 2 range and con ductance were recorded by a Tesla Conductivity Bridge.3 C. M. G u p t a , Bull. chem. Soc. Japan 33, 837 [1966]. 4 M. P. J o s h i and C. M. G u p t a , Ind.

Amperometric titrations

“…The titration of CrCl3 or ferric alum with potassium hydroxycyanotungstate(IV) has been used to study the compositions of the complexes so produced (124). The compositions of uranyl isopolytungstates have been examined by amperometric titrimetry (121). Other titrations that involve tungstate are with silver (242) or lead (88).…”