Abstract
Bismuth (III) ion reacts with thiourea to form yellow water-soluble complex in an acidic solution. This complex can be extracted into methyl isobutyl ketone (MIBK) or ethyl acetate as an ion pair with perchlorate ion. The extracted species gave an absorption maximum at 472 nm in each solvent, and the molar absorption coefficients at 472 nm were 1.04×104 (in MIBK) and 1.07×104 cm-1 mol-1 dm3 (in ethyl acetate). The effect of the concentrations of perchlorate ion and thiourea on the distribution ratio of bismuth was investigated, and it was concluded that the composition of the extracted species was [Bi (thiourea)2] (ClO4)3. The conditional formation constant of bismuth-thiourea complex, the ion association constant between the complex and perchlorate ion, and the distribution constant of the extracted species were determined at the ionic strength of 3.60 mol dm-3 at 25°C. The respective values obtained in MIBK extraction system were 3.0×10, 0.085 and 6.0, and those in ethyl acetate extraction system were 5.2×10, 0.028 and 7.9, respectively. The reaction among bismuth (III) ion, thiourea and perchlorate ion in aqueous solution was then investigated spectrophotometrically at the ionic strength of 3.60 mol dm-3. Two species, [Bi (thiourea)2] and [Bi(thiourea)2]-(ClO4)3, were formed, and their molar absorption coefficients at 468 nm (absorption maximum wavelength) were 6.0×103 and 8.4×103cm-1 mol-1 dm3, respectively. The constants obtained at 24.2°C for the complex formation and ion association were 3.2×10 and 0.14, respectively. In addition, the ΔH and ΔS values obtained for the complex formation were -19 and -35, respectively, and those for the ion association were -7.7 kJ mol-1 and -45 J mol-1 K-1, respectively.
