E5 Fr

SPECTROPHOTOMETRIC DETERMINATION OF THE EQUILIBRIUM CONSTANT OF A REACTION

M. L. SANGA

CHEMICAL ENGINEERING, COLLEGE OF ENGINEERING

UNIVERSITY OF THE PHILIPPINES, DILIMAN, QUEZON CITY, PHILIPPINES

DATE PERFORMED: JANUARY 15, 2014

INSTRUCTOR’S NAME: MOISES JEROME GARRERO

______________________________________________________________________________________________________________________________

ABSTRACT

The experiment aimed to determine the equilibrium constant Keq of the formation of Fe(SCN)2+ from Fe3+ and SCN- in the equation Fe3+(aq) + SCN-(aq) ⇌ Fe(SCN)2+(aq), through spectrophotometric analysis. Acidified solutions (using 0.1 M HCl) of FeCl3 and KSCN were prepared for the calibration of the UV-Vis spectrophotometer (using standard solutions) and the determination of Keq of the Fe(SCN)2+ formation (solutions with unknown concentrations). Absorbance readings of the standard and unknown solutions were obtained through the spectrophotometer. The equation of the trend line of the calibration curve (obtained through the plot of the absorbance readings vs. thiocyanatoiron (III) ion concentration of the standard solutions) is given by y = 4041x – 0.049. Using the absorbance readings and the application of the Beer-Lambert Law on the trend line equation, the average experimental Keq was computed to be 190.85 with a 30.72 % deviation from the theoretical value. Based on the results of the experiment, it can be assessed that the experiment was successful.

______________________________________________________________________________________________________________________________

INTRODUCTION

Spectrophotometry, a branch of spectrometry, is a group of instrumental techniques that measures the atomic and molecular energy levels of a substance [1]. In spectrophotometry, the emission and absorption spectra’s wavelengths identify and measure the concentration of a substance. The wavelength at which the substance’s absorbing ions or molecules has a...