Fr 1 Spectrophotometric Determination of the Equilibrium Constant of a Reaction
Topics: Chemical reaction, Light, Concentration, Solution, Chemistry, Chemical equilibrium / Pages: 5 (1062 words) / Published: Jan 7th, 2013

Spectrophotometric Determination of the Equilibrium Constant of a Reaction

DEPARTMENT OF MATERIALS, METALLURGICAL AND MINING ENGINEERING, COLLEGE OF ENGINEERING
July 26, 2012
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ABSTRACT
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Before proceeding to test the next solution, we must first clean the cuvette, using similar steps earlier. First, we rinse with water, then with the solution, and then we fill it up and test. We tested for the wavelength standard 5 at which there was maximum absorption. At this wavelength, we tested the absorbance of all the standards.

Table 1: Volumes and Concentrations of Standards and Analysis Standard in ml | | | 0.002M FeCl3 | 0.2M KSCN | 0.1 M HCl | 0 | 5 | 5 | 1 | 5 | 4 | 2 | 5 | 3 | 3 | 5 | 2 | 4 | 5 | 1 | 5 | 5 | 0 | Analysis in ml | | | 0.002M FeCl3 | 0.2M KSCN | 0.1 M HCl | 0 | 3 | 11 | 2.1 | 3 | 8.9 | 2.3 | 3 | 8.7 | 2.5 | 3 | 8.5 | 3 | 3 | 8 | 4 | 3 | 7 | The experiment determined the equilibrium constant for the formation of the FeSCN2+ complex. Using a spectrophotometer, the absorbance of FeCl3, KSCN and HCl standard solutions of known concentration was measured and graphed to determine the absorptivity coefficient. This coefficient was then used to calculate the actual concentrations of the FeSCN2+ complex. Having the initial concentration of Fe3+ and SCN- ions along with the complex, the equilibrium constant can be determined. INTRODUCTION The equilibrium constant (Keq) relates the concentrations of the reactants and products in a reaction in equilibrium. However, the Keq cannot be determined with calculations because only the concentrations of reactants are known. By using a spectrophotometer, the products’ properties can show the concentration of the product using Beer-Lambert’s Law, which relates Absorbance and concentration. METHODOLOGY 250 ml of 0.1M HCl, 100 ml of

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