chemical thermodynamics of neptunium and plutonium - U.S. ...

396 19. Plutonium group 16 compounds and complexesTable 19.3: (continued)Reference log 10 ∗ β I m log 10 ∗ β ◦ t( ◦ C)[76BAG/RAM2] (4.59±0.11) 2.2 (HClO 4 ) (7.32±0.21) 25(4.45±0.11) 2.2 (HClO 4 ) (7.18±0.21) 25[77BAG/RAM] (4.58±0.01) (a) 2.2 (HClO 4 ) 10(4.38±0.05) (a) 2.2 (HClO 4 ) 10[83NAS/CLE] (4.10±0.09) (a) 2.2 (H,Na)ClO 4 0(4.06±0.07) (a) 2.2 (H,Na)ClO 4 10(4.13±0.07) 2.2 (H,Na)ClO 4 (6.86±0.19) 25(4.11±0.08) (a) 2.2 (H,Na)ClO 4 35Best Value (4.43±0.01) 2.2 (7.18±0.32) 25(a) Used to calculate r H ◦ m only.The most reliable value of log ∗ 10 β ◦ (I)(19.5) atI = 2.2 m is the weighted averageof the results at 25 ◦ C reported in Table 19.3: (4.43 ± 0.01). Based on theionic interaction parameters determined for the analogous U(IV) complex (ε(19.5) =−(0.46 ± 0.08) kg·mol −1 ;[92GRE/FUG]), this value can be extrapolated to standardstate: log10 ∗β◦∗2(19.5) = (7.18 ± 0.32). Caution is advised in the use of log10 β◦ 2 (19.5)outside of the range of H + concentration (1-2 M) in which it was determined. Thereare four independent sets of equilibrium constants determined in identical experimentsover a range of temperatures from which to estimate r Hm ◦ (19.4) and rHm ◦ (19.5):[73PAT/RAM] (including results of [76PAT/RAM]), two from [77BAG/RAM] (includingthe results of [76BAG/RAM] and[76BAG/RAM2]), and [83NAS/CLE]. The fourdeterminations yield r Hm ◦ (19.4) =−(7.1±1.7), (2.4±3.5), (7.2±3.0), and (18.6±1.2) kJ·mol −1 and r Hm ◦ (19.5) = (3.1 ± 1.8), (8.6 ± 1.4), (7.5 ± 2.3), and (1.5 ±3.4) kJ·mol −1 . The unweighted average of these results is indistinguishable from 0( r Hm ◦ (19.4) = (5.3 ± 21.3) kJ·mol−1 and r Hm ◦ (19.5) = (5.2 ± 6.8) kJ·mol−1 ).Aswe have no basis to eliminate any of these experimental results, we recommend no bestvalue, and advise caution in the determination of fundamental thermodynamic propertiesfrom the temperature variation of log ∗10 β 1(19.4) and log ∗10 β 2(19.5) in this system.19.1.1.1.d Pu(III) sulphatesThere are four experimental data sets concerning the Pu(III)-sulphate system(Table 19.4). Although Pu(III)-bisulphate complexes have been postulated(Pu(HSO 4 ) + 2 ,andPu(SO 4)(HSO 4 )(aq); [67NAI/RAO], [83NAS/CLE2]), the resultsare interpreted by this review as consistent with the equilibria:Pu 3+ + HSO − 4Å PuSO + 4 + H+ (19.6)