CHEM10006 Lecture Notes - Lecture 33: Water Softening, Transition Metal, Hematite

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The acidity of the aqua complex depends on the charge of the metal ion. Equilibrium is further to the right for an fe3+ complex than an fe2+ complex. Oxido and hydroxide anions bridge metal ions to make large insoluble structures. Aqua complexes tend to be discrete and soluble. With no o2 present, h+ was the strongest oxidant in the primitive earth; In an oxygenless environment, iron was only avaiable as fe2+, as it could not have been oxidised by. Fe2+ is incorporated into many enzymes that use the feiii and feii couple to catalyse one-electron redox reactions - fe(ii) more stable. O2 present in the atmosphere - the o2/h2o becomes important. Thus fe(ii) will be oxidised to fe(iii) - fe(iii) more stable. Fe3+ solubility depends on ph stable at < 3-4, rust stable at > 3-4, haematite stable under anhydrous conditions. Cadmium: soluble but not as abundant as zn; Zinc: soluble and available as zn2+ (aq)