Spectrophotometric Determination of the Ligand/metal Ratio and Kf in a Complex Ion

Spectrophotometric Determination of the Ligand/Metal Ratio and Kf in a Complex Ion

Objectives: Three methods of spectrophotometric techniques were used in this experiment to determine the ligand: mole ratio for coordinate compounds in solution. The three methods used included the Mole Ratio Method, the Slope Ratio Method, and JobЎЇs Method of Continuous Variation. JobЎЇs Method was used to determine the stability constant, Kf, for the reaction. The Slope Ratio Method was used to determine the molar absorptivity, ¦Е, for the ligand-metal complex.

Introduction: Transition metals form coordinate covalent bonds with Lewis bases to make coordination complexes. The anion or neutral compound reacting with the metal are called ligands. A general reaction for the formation of the complex follows:

One of the characteristics of transition metal complexes is that they absorb light in the visible region of the spectrum. The instrument used for analysis is a spectrophotometer. The instrument works by passing a beam of light through a cuvette, which contains the solution in a closed chamber. The beam passes through the sample and into a detector. The detector measures the intensity of the light that was passed through the solution, as a measurement of percent transmittance. Photons are passed through the solution and the absorbing species transitions to a higher energy state.