Experiment 1 - Spectrophotometric Determination of the Stability constant of a Complex Ion

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Experiment 1 Spectrophotometric Determination of the Stability constant of a Complex Ion Student Name: Adam Sadowski Student Number: 1000142071 Other Member(s) of the Team: Kartik Moza Practical Section Number: 0122 Date the Experiment was Performed: 16/01/2013 Date the Report was Submitted: 25/01/2013 Submitted to Dr. I-San Chan
2 Purpose Knowing various stability constants is relevant to our safety and economy when considering which solutions will react with and damage water-supplying drainage pipes; these constants are quantified representations of a reaction’s direction and extent when the concentrations of its ions or gaseous atoms are not in equilibrium. Complex ions can be the products of mixing metal ions (as the Lewis acids) with ligands (as the Lewis bases). Transition metal cations, such as iron (III), can produce especially stable complex ions when reacted with ligands such as SCN - . In this experiment, ferric ions reacted with thiocyanate ions to form complex ions of one form: Fe +3 (aq) + SCN - (aq)  Fe(SCN) +2 (aq) The above is a reversible equation omitting the water, whose concentration is nearly constant, and for which the stability constant is K = [Fe(SCN) +2 ]/[Fe +3 ][SCN - ] . This constant has been determined in steps: 1) by mixing solutions with an excess of thiocyanate ions and utilizing a spectrophotometer to acquire absorbance values for differing concentrations of complex ion; 2) by mixing solutions without an excess of either reactant to thereby establish

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