Spectrophotometric methods for the determination of cerium with thenoyltrifluoroacetone (TTA) were developed by Khopkar and De, and Onishi and Banks. The composition of the cerium-TTA complex extracted with xylene from 1
N sulfuric acid solution containing bromate (the conditions of Onishi and Banks) is probably CeT
4, where HT is the enol form of TTA. The extraction constant of this system is calculated to be 2×10
3. An attempt to obtain a precipitate of the complex under similar conditions was not successful.
The composition of the cerium-TTA complex extracted under Khopkar and De's conditions could not be determined, because the plot of log
DCe versus log [TTA] was not a straight line (
DCe : distribution ratio of cerium). Apparent molar absorptivities for cerium (IV) in benzene are 4.1×10
3 and 3.6×10
3 at 440 and 450mμ, respectively.
Although Khopkar and De suggested the oxidation of cerium(III) by bromate and dichromate in slightly acid solution, this oxidation is incomplete. The oxidation of cerium(III) (1020mg) is almost complete when 10m
l of a solution that is 1
N in sulfuric acid and 0.3
M in sodium bromate is heated at 70°C for 1 hour.
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