Spectrophotometric Determination of Equilibrium Constant...

DATE PERFORMED: JULY 20, 2007 SPECTROPHOTOMETRIC DETERMINATION OF EQUILIBRIUM CONSTANT FOR A REACTION ABSTRACT UV-VIS spectrophotometry is one of the most widely-used methods for determining and identifying many inorganic species. During this experiment, this spectrophotometry was used to determine the equilibrium constant, Keq, of the Fe3+(aq)+SCN-(aq)↔ FeSCN2+(aq) reaction. By determining the amount of light absorbed, the concentration of the colored FeSCN2+ solution was also quantitatively determined. From that data, the concentrations of the reagents at equilibrium may also be determined. This experiment should thus provide a Keq value without computing for the concentration of each of the species in the reaction. This†¦show more content†¦Beer’s Law states that absorbance is directly proportional to the concentration c of the absorbing species, and to the path length b of the absorbing medium by a proportionality constant called the absorptivity a. In our experiment, we expressed the concentration of the absorbing species in terms of mol/L and the path lengt h in centimetres. Thus, the proportionality constant becomes the molar absorptivity ÃŽ µ. We set the wavelength of the spectrophotometer to 447 nm so we could achieve maximum sensitivity. At this point, the change in absorbance per unit of concentration is greatest and there is greater adherence to Beer’s Law. Table I. Absorbance of Unknown Solutions |Solution |Absorbance |[Fe3+]init |[SCN-]init | |Unknown 1 |0.158 |0.001 |2.00 x 10-4 | |Unknown 2 |0.308 |0.001 |4.00 x 10-4 | |Unknown 3 |0.457 |0.001 |6.00 x 10-4 | |Unknown 4 |0.604 |0.001 |8.00 x 10-4 | |Unknown 5 |0.743 |0.001 |1.00 x 10-3 | Table II. Determination of the Equilibrium Constant, Keq |Solution |[Fe3+] |[SCN-] |[[Fe(SCN)]2+] |Keq | |Unknown 1 |9.57 x 10-4 |1.57 x 10-4 |4.34 x 10-5Show MoreRelatedChemical Equilibrium and Santa Monica College3366 Words   |  14 PagesChemistry 12 Santa Monica College Determination of Kc for a Complex Ion Formation Objectives †¢ †¢ Find the value of the equilibrium constant for formation of FeSCN2+ by using the visible light absorption of the complex ion. Confirm the stoichiometry of the reaction. Background In the study of chemical reactions, chemistry students first study reactions that go to completion. Inherent in these familiar problems—such as calculation of theoretical yield, limiting reactant, and percent yield—isRead MoreThe Spectrophotometric Determination of an Equilibrium Constant1968 Words   |  8 PagesThe Spectrophotometric Determination of an Equilibrium Constant. Abstract: The report presents determination of equilibrium constant for the formation of a complex ion FeSCN2+. This was accomplished using a colorimeter to measure absorbance of some known concentration solutions in order to generate the calibration curve. The equation of the graph was used to compute the equilibrium concentrations of the reactants and products, needed to calculate the equilibrium constant forRead MoreVolumetric Analysis1212 Words   |  5 Pagesthe reagent solution -the titrant-are added to the analyte until their reaction is complete. 3. The most common titrations are based on: - acid-base - oxidation-reduction - complex formation and - precipitation reactions 1. Methods of determining when the analyte has been consumed include: - detecting a sudden change in the voltage or current between a pair of electrodes - monitoring a spectrophotometric absorbance change - observing an indicator color change 1Read MoreSpectrophotometric Determination of the Acid Dissociation Constant of Methyl Red3606 Words   |  15 PagesDate Performed: September 9 ,2011 SPECTROPHOTOMETRIC DETERMINATION OF THE ACID DISSOCIATION CONSTANT OF METHYL RED M.C. Caligagan ,M.N.Q. Tolentino and M.Q. Clores Institute of Chemistry, College of Science University of the Philippines, Diliman, Quezon City, Philippines Received :September 21,2011 ABSTRACT This experiment aims to determine the acid dissociation constant value of Methyl Red by means of spectrophotometry. Ten samples were spectrophotometrically analyzed under a UV-Vis