# Spectrophotometric Determination of Equilibrium Formal Report

Topics: Mathematics, Concentration, Solution Pages: 7 (1281 words) Published: July 15, 2014
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Spectrophotometric Determination of Equilibrium Formal Report Matt DeLuca
The Department of Chemistry, SUNY College at Brockport
Brockport, NY 14420
CHM 206.04

Abstract:

The main objective of this experiment was incorporating the use of spectrophotometry in an attempt to study the position of equilibrium. Furthermore, after the completion of this experiment, the formation of the equilibrium constant of the iron thiocyanate complex could be determined. In order to accomplish these tasks, five different solutions were made. Upon completion of the experiment, the results of the aforementioned experiments were calculated to an average of the final formation constant of 183.

Introduction:

The experiment for the Spectrophotometric Determination of Equilibrium had the main objectives of determining the position of equilibrium and the formation of the equilibrium constant of the iron thiocyanate complex. In order to do so, the use of a spectrophotometer was incorporated into the experiment. In order to obtain an accurate end result, the absorbance of five various samples was used.

In order to determine the formation equilibrium, the constant obtained from Beer’s Law was factored into the calculation. The equation for Beer’s Law is A=bbc. It is important to note that Beer’s Law states that the concentration of a solution is directly proportional to the absorbance. Formally, Beer’s Law relates two factors; the absorption of light, and the properties of the material through which the light is traveling through. Upon further examination of the equation for Beer’s Law, each variable has a corresponding purpose within the overall equation. ‘A’ represents the absorbance of light, and ‘’ is representative of the molar absorptivity. It is also important to note that  is highly dependent upon the species measured and its respective wavelength. ‘B’ represents the optical path length of the containing the absorbing solution and is measured in centimeters. Finally, ‘C’ is a measure of the molarity of the absorbing species. In order to study the position of equilibrium and the formation of the equilibrium constant, within the realm of the experiment, the absorbance was used for the purpose of monitoring the changes in concentration.

The iron thiocyanate complex formation can be observed below: Fe3+ (aq) + SCN- (aq)  FeSCN2+ (aq) In order to complete the calculations required within this experiment, the equilibrium equation was needed. This equation is an accurate representation of the bonding between two molecules. The iron thiocyanate complex formation equation can and will lead to the respective equilibrium constant expression seen below: Kf = [FeSCN2+] [Fe3+][SCN-]

This equilibrium constant expression represents the concentrations of the products over the concentrations of the reactants. In order to accurately determine the equilibrium constant expression, the products or reactants which represent concentrations in the liquid or solid state must be omitted from the equation. The use of the equilibrium constant expression was of paramount importance because the absorbance of light is proportional to the concentration of the absorbing species in solution for any given absorbing species at a specific wavelength. The thickness of the solution through which light passes is also proportional to the absorbance.

The use of a spectrophotometer was utilized for the purpose of determining the absorbency of five different solutions. After the respective absorbency of each solution was determined, the formation equilibrium constant of the iron thiocyanate complex was calculated.

Experimental Method:
The five different solutions required in this experiment were prepared in...

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