Studies on metal oxalate complexes. I. Validation of the reversibility of the Hg,Hg2C2O4(s) electrochemical couple

A second kind electrode, based on the Hg,Hg2C2O4(s) couple, is proposed for the potentiometric determination of the oxalate ion concentration. The nernstian behaviour of the electrochemical couple is demonstrated not o nly by analyses of solutions with a known content of C2O42- bur also by det ermining, in 1M NaClO4 at 25 degrees C, the equilibrium constants of the fo llowing reactions Hg2C2O4(s) = Hg-2(2+) + C2O42- (1) logK(s) = -11.19 +/- 0.05 nH(3)O(+) + C2O42- = HnC2O4(n-2) + nH(2)O (2) with n = 1,2 and the formation constants log beta(1) = 3.57 +/- 0.02 and log beta(2) = 4.57 +/- 0.02 The electrode was also employed to study potentiometrically the complex for mation between uranyl and oxalate. At [H+] congruent to 0.1M and U(VI) conc entrations not exceeding 0.020M, only mononuclear species are formed, accor ding to the following general reaction UO22+ + pC(2)O(4)(2-) = UO2(C2O4)(p)((2-2P)) (3) with p = 1,2,3. The overall stability constants, written as log(beta(1p) +/ - 3 sigma), are the following: log beta(11) = 6.03 +/- 0.03 log beta(12) = 10.87 +/- 0.07 log beta(13) = 1 4.0 +/- 0.3.