Treat your data sets independently. Enter your data in two columns in a spreadsheet. Your goal is to plot In K vs. 1/T (remember to use the absolute temperature). To determine K, you need to calculate the concentrations of all species that appear in the equilibrium expression. Do this as follows: [COC142-]: Use Beer's Law to calculate this concentration ( = 572 L mol-1 cm-1). However, you need to "adjust" your measured absorbance. Since both compounds absorb at 692 nm, not all of the light absorbed is due to the blue, chloride species. A small amount is due to the pink, aquo complex. Fortunately, this is a small amount, but it becomes important when the concentration of the chloro complex is very low. To compensate, divide the absorbance of the [Co(H2O)6]2+ at 511 nm by 29 ( this is the ratio of the molar absorptivity of this complex at 512 nm to that at 692 nm) and subtract this value from every absorbance measurement in your data set.* Use this "adjusted" absorbance to calculate the CoC142- concentration. *Note that this approach assumes that the concentration of [Co(H20)6]2+ does not change. While this is not true, the relative change in concentration is small enough that it does not introduce significant error. [Co(H20)62+]: Use the total cobalt concentration of the solution and the concentration of the CoC142- to calculate [Co(H2O)6]2+ by the following equation:[Co2 +Jtotal [CoC142-]+[Co(H2 0)62+] [CI]: Assume this to be 4.0, the molarity of the acid solvent, at all temperatures, i.e., assume that the change in chloride concentration is negligible as the reaction progresses. Using these three concentrations, calculate K for each temperature. Is it increasing or decreasing? Why? Prepare a graph of In K vs. 1/T and calculate EH and S. Repeat the analysis for your second data set. Average your two values for each quantity. Post-Lab Questions 1. Using your values of H and IIS, explain the temperature dependence of the equilibrium constant for your reaction using LeChatelier' s Principle. 2. From a molecular level, interpret the S value for the reaction. THE TEMPERATURES ARE 10-90 CELSIUS AND THE ABSORBANCE CAN BE MADE UP NUMBERS

Treat your data sets independently. Enter your data in two columns in a spreadsheet. Your goal is to plot In K vs. 1/T (remember to use the absolute temperature). To determine K, you need to calculate the concentrations of all species that appear in the equilibrium expression. Do this as follows: [COC142-]: Use Beer's Law to calculate this concentration ( = 572 L mol-1 cm-1). However, you need to "adjust" your measured absorbance. Since both compounds absorb at 692 nm, not all of the light absorbed is due to the blue, chloride species. A small amount is due to the pink, aquo complex. Fortunately, this is a small amount, but it becomes important when the concentration of the chloro complex is very low. To compensate, divide the absorbance of the [Co(H2O)6]2+ at 511 nm by 29 ( this is the ratio of the molar absorptivity of this complex at 512 nm to that at 692 nm) and subtract this value from every absorbance measurement in your data set.* Use this "adjusted" absorbance to calculate the CoC142- concentration. *Note that this approach assumes that the concentration of [Co(H20)6]2+ does not change. While this is not true, the relative change in concentration is small enough that it does not introduce significant error. [Co(H20)62+]: Use the total cobalt concentration of the solution and the concentration of the CoC142- to calculate [Co(H2O)6]2+ by the following equation:[Co2 +Jtotal [CoC142-]+[Co(H2 0)62+] [CI]: Assume this to be 4.0, the molarity of the acid solvent, at all temperatures, i.e., assume that the change in chloride concentration is negligible as the reaction progresses. Using these three concentrations, calculate K for each temperature. Is it increasing or decreasing? Why? Prepare a graph of In K vs. 1/T and calculate EH and S. Repeat the analysis for your second data set. Average your two values for each quantity. Post-Lab Questions 1. Using your values of H and IIS, explain the temperature dependence of the equilibrium constant for your reaction using LeChatelier' s Principle. 2. From a molecular level, interpret the S value for the reaction. THE TEMPERATURES ARE 10-90 CELSIUS AND THE ABSORBANCE CAN BE MADE UP NUMBERS

Fundamentals Of Analytical Chemistry

9th Edition

ISBN:9781285640686

Author:Skoog

Publisher:Skoog

Chapter7: Statistical Data Treatment And Evaluation

Section: Chapter Questions

Problem 7.9QAP

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