Under certain condition, Pr(IV,III) basic carbonates are soluble in aqueous solution of malonic acid to yield an yellow complex Pr(IV)-CH2(CO2)22- which shows a broad characteristic absorption band at 265 nm. The complex composition ratio of Pr(IV)-CH2(CO2)22- determine by equilibrium shift is 1:2. Reduction kinetics of Pr(IV)-OH2(CO2)22- complex in aqueous solution is pseudo a first order reaction for Pr(IV). The various factors effecting the stability of Pr(IV)-CH2(CO2)22- complex in the solution were also studied by spectrophotometric methods.

Key words: SPECTROPHOTOMETRY, STABILITY, AQUEOUS SOLUTION, REACTION KINETICS, REDUCTION, EDTA, XYLENOL ORANGE, IODOMETRY, MALONIC ACID, PRASEODYMIUM