conclab8 - affect the product’s concentration measured...

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Calculation of an Equilibrium Constant via Absorption Spectroscopy For this lab, the objective was to determine an equilibrium constant (K) for a reaction where the reaction product is colored- in this case, the color was orange-red. The three main sources for this determination were absorption spectroscopy, Beer’s Law, and LaChatelier’s principle. First, a working solution of Fe(NO 3 ) 3 was made and mixed with KSCN and HNO 3 , and then it’s absorbance was measured in order to form a calibration curve. This calibration curve, representing the Beer’s law plot, contains a trendline with the slope that represents the “E” in Beer’s law equation (A=EbC). Next, Fe 3+ , SCN - , and HNO 3 , were mixed again with different volumes, this time as “unknowns”, and their absorbance were measured. The absorbance was measured using 470nm, providing maximum sensitivity. Had 400nm or 500nm wavelengths been used, these changes would
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Unformatted text preview: affect the product’s concentration measured because absorbance and concentration are directly related in Beer’s Law. Therefore, a change in absorbance would provide a different value for C (concentration). These absorbance values were used to calculate the concentration of the product Fe(SCN) 2 in order to determine the concentrations of each species at equilibrium. Using the concentration of the product, the concentrations of the reactants at equilibrium are found using an ICE chart. With these concentrations, the solutions for the value, K, can be calculated with the equation for equilibrium. Specifically, the average value of K found was 92.99, a relatively large value for K. When K is large, this means that at equilibrium, the concentration is mostly in the products of the equation, in this case the product is Fe(SCN) 2 ....
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