Separation and identification of chloride, bromine and iodine anions: An education proposition in qualitative analytical chemistry

Abstract

Qualitative analytical chemistry course features the study of cations and anions, approaching identification and separation of these species. Cations are classified into groups and analyzed systematically, according to their similarities. Several analytical methods have been proposed for anion determination. However, a practical difficulty to analyze certain anions mixtures is notable, due to chemical incompatibility or even to similarity between these species. The objective of this study was to develop a methodology for separation and identification of chloride (Cl-), bromine (Br-) and iodine (I-) anions for practical classes. Precipitation of anions Cl-, Br-and I-was carried out using silver nitrate reagent. Part of formed precipitate was solubilized with ammonium hydroxide, resulting on Cl-separation from other anions. Identification of Cl-anion was performed by shifting equilibrium reactions that lead to silver chloride formation, a white-colored solid. The precipitate, containing Br-and I-anions, was solubilized by thioacetamide, which aimed to release sulfide ions into silver sulfide form. I-anion was oxidized to elemental iodine and characterized by chloroform extraction. Br-anion characterization was possible due to an oxidation of elemental bromine anion and subsequent extraction with chloroform, presenting an orange color at such stage.