Spectrophotometric Determination of Iron(III)-Glycine Formation Constant in Aqueous Medium Using Competitive Ligand Binding

Division of Chemical Education of the American Chemical Society. Subscription Department, P.O. Box 1267, Bellmawr, NJ 08099-1267. Tel: 800-691-9846; Tel: 856-931-5825; Fax: 856-931-4115; e-mail: [email protected]; Web site: http://www.jce.divched.org

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Teachers

Science Laboratories; Science Experiments; Teaching Methods; Spectroscopy; Science Instruction; Laboratory Experiments; Undergraduate Study; College Science; Computer Uses in Education; Computer Software; Chemistry; Computation

0021-9584

The formation constant of iron(III) complex with glycine (Gly) ligand in aqueous acidic medium (0.2 M HNO[subscript 3], I = 0.2 M at 28 plus or minus 1 degree C) was determined spectrophotometrically in which a competing color reaction between Fe(III) and SCN[superscript -] was used as an indicator reaction. Under the specified conditions Fe(III) formed 1:1 complexes, [Fe(SCN)][superscript 2+] and [Fe(Gly)][superscript 2+], with both of these ligands. The molar absorption coefficient and the formation constant of the [Fe(SCN)][superscript 2+] complex were determined graphically as well as through dynamic optimization of six parallel equations using Solver tool in Excel. Values thus obtained were subsequently used to calculate concentrations of uncoordinated iron(III) and glycine in the mixed-ligand solution. The principal advantage of the proposed method is that it offers a simple and convenient approach for an undergraduate laboratory demonstration of quantitative comparisons of formation constants using an inexpensive spectrophotometer and Excel software that are readily available in most teaching laboratories. (Contains 2 figures and 2 tables.)

As Provided

16

2009

EJ832505