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Chemistry 112 Chemical Equilibrium

Chemistry 112 Chemical Equilibrium - Drew Rasmussen...

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Drew Rasmussen Chemistry 112 Lab – 011 Partner: Andy Zola Instructor: Katri Truhler March 3, 2011 Chemical Equilibrium Laboratory Write-up A. Research Question a. What is the experimentally determined K c for the reaction at room temp? b. What is the sign of Delta-H for the reaction? What does this mean? c. What were the effects of adding/removing reactants to/from the equilibrium mixture? (Fe(NO 3 ) 3 and EDTA) B. Theoretical Approach a. In this lab an equilibrium constant (K c ) was determined experimentally using the reaction Fe 3+ (aq) + SCN - (aq)  FeSCN 2+ (aq). To determine the constant, an equilibrium equation was created (and can be found on page 85) from the balanced equation of the reaction. Using spectrophotometry and the relationships between A eq and A std , it was possible to determine the concentration of FeSCN 2+ at equilibrium. Since the reaction is a 1:1 reaction (1 mole of SCN - produces 1 mole of FeSCN 2+ ) it is possible to solve for both Fe 3+ and SCN - at equilibrium, by using the three known concentrations, and then ultimately solving for K c in the end. b. For this equilibrium reaction Le Chatelier’s Principle was also studied and observed. This principle is important because when a variable is introduced into the reaction (such as heat, or Fe(NO 3 ) 3 ), the equilibrium of the reaction will adjust accordingly. This principle also explains temperature and allowed the question what is the sign of Delta-H to be answered. By having four different test tubes,
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and recording a standard A 470 and then introducing heat, removing heat, and adding other solutions this principle was further tested. C. Observations and Results a. FeSCN 2+ is an orange-red color, and is not very viscous. It’s almost the color of the orange tootsie pops. At room temperature, the stock solution had an Abs. of 0.969 @ 468.54nm. b.
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Chemistry 112 Chemical Equilibrium - Drew Rasmussen...

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