The Chemical EducatorISSN: 14304171 (electronic version) Abstract Volume 17
(2012) pp 038041 Mistake in the Considerations of Hydrolysis Constants and Chlorideion Complex Formation on the Solubility of Rare Earth ElementsHilario LópezGonzález*^{,†}, Alberto RojasHernández^{‡} † Instituto Nacional de Investigaciones Nucleares.
Dirección de Investigación Científica, Gerencia de Ciencias Básicas,
Departamento
de Química. Apdo. Postal 181027, 11801, México, D. F., hilario.lopez@inin.gob.mx;
‡Universidad Autónoma Metropolitana.
Departamento de Química. Área de Química Analítica, Apdo. Postal 55534, 09340,
México, D. F. Published: 16 March 2012 Abstract. Simplifications of chemical calculations are used frequently in teaching general and analytical chemistry to undergraduate students. However, oversimplifications can give inconsistent solutions to chemical calculation problems. In this paper we discuss this topic over a common example of solubility calculations of the Ln(III) hydroxide in 2M at 303 K. The procedures for the calculation of the solubility of rare earth elements (REE) considering both hydrolysis and chlorideion complex formation are presented. Solubility products (K_{sp}), hydrolysis (b_{Ln,H}), and chloridecomplex stability (b_{Ln,Cl}) constants for lanthanum, praseodymium, and lutetium in 2MNaClO_{4} and 2MNaCl at 303K were taken from the literature. It is important to distinguish between the minus logarithm of the hydronium concentration (pC_{H}) and the experimental pH value measured in systems with high ionic strength. According to the results, when pC_{H(sat)} £ pb_{Ln,H} – 1, Ln^{3+} is the only soluble species; for the interval pb_{Ln,H} – 1 < pC_{H(sat)} < pb_{Ln,H} + 1, a twosolubilityequilibrium model is required due to the presence of the soluble first hydrolysis species, (Ln(OH)^{2+}). Moreover, for a high chlorideion concentration a soluble chloride complex may also be relevant. In fact, Ln(OH)^{2+} controls the behavior of the highcharge density REE, whereas LnCl^{2+} is the most import for the lowcharge density REE.
Key Words: In the Classroom; general chemistry; analytical chemistry (*) Corresponding author. (Email: hilario.lopez@inin.gob.mx) Article in PDF format (118 KB) HTML format
