experiment 34 formal.docx - Sabrina Fregoso Professor...

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Sabrina Fregoso Professor Farnum Chem 112 MW 7:35 am 27 September 2018 Experiment 34: An Equilibrium Constant
Abstract: In this experiment, the equilibrium constant of a chemical system was determined using a spectrophotometer. This process was done using a spectrophotometer connected to the Pasco Capstone software to determine the absorbance and percent transmittance. First, a set of standard solutions were prepared and calibrated through a spectrophotometer to establish a calibration curve from the absorbance and percent transmittance. Then that same process was followed to get the absorbance for a set of test solutions. The data collected in the first part was plotted using Microsoft Excel. The equilibrium constant for a soluble equilibrium was determined through calculations using the slope from the calibration curve. As a result, the average magnitude of an equilibrium constant, K c , was ~ 309.36. The standard deviation of K c was ~55.025. The relative standard deviation of K c was ~17.79%RSD. The quality of the data taken through the Pasco Capstone software was executed well and the graphs that were as a result, were neat and precise. Introduction: The main objective of this experiment is to determine the equilibrium constant, K c , of a set of test solutions. This objective will be met by conducting a series of chemical mixtures and gathering the absorbance and transmittance using a spectrophotometer connected to the Pasco Capstone software. The Pasco software constantly records the absorbance and percent transmittance simultaneously. There is a total of five test solutions that have 5 mL of 0.002 M Fe(NO 3 ) 3 , different volumes (mL) of 0.002 M NaSCN, and different volumes (mL) of 0.1 M HNO 3 . The overall reaction is expressed as: Equation 1: Fe 3+ (aq) + SCN - (aq) ↔ FeSCN 2+ (aq) It is assumed that the position of the equilibrium is driven so far to the right due to the excess Fe 3+ , this as a result complexes all the SCN - to form FeSCN 2+ . Spectrophotometric methods involve the interaction of electromagnetic (EM) radiation with matter. The most common EM spectrums used for analysis are the ultraviolet, visible, and infrared regions. The degree of absorbed radiation or the intensity of the transmitted radiation is measured using a spectrophotometer, which measures transmitted light intensities with photosensitive detector at a specific visible wavelength. The wavelength that the absorbing ions or molecules have a maximum absorption of visible radiation is determined and set in the

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