Experiment 10

Experiment 10 - Trevor Austin December 2 2004 Experiment#10...

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Unformatted text preview: Trevor Austin December 2, 2004 Experiment #10: Chemical Equilibrium: Determination of an Equilibrium Constant Experiment #10: Chemical Equilibrium: Determination of an Equilibrium Constant A. SUMMARY In this experiment we evaluated the equilibrium constant for adding an iron(III) solution to a thiocyanate solution to form thiocyanoiron(III). When the iron(III) is added to thiocyanate it does not react to completion, instead ions of the product and reactants can be found in the final solution. In the experiment we measured the absorbance of blue light solutions of different concentrations. From this data an equilibrium constant will be calculated in the calculations section. B. RESULTS Trial (#) 1 2 3 4 Standard Solution Trans (%T) 73.31 80.18 63.59 53.85 8.65 Absorbance 0.135 0.096 0.197 0.269 1.063 C. GRAPHS AND CALCULATIONS Equilibrium reaction: Fe3+ (aq) + SCN- (aq) FeSCN2+ (aq) 1. Calculate initial concentration of Fe3+. [Fe3+]i = ((Fe(NO3)3) mL / total mL) * (0.0020 M) [Fe3+]i = (5 mL / 10 mL) * 0.0020 M [Fe3+]i = 0.0010 M 2. Calculate the initial concentration of SCN-, based on its dilution by Fe(NO3)3 and water. [SCN-]i = (KSCN mL / total mL) * 0.0020 M [SCN-]i = (2 mL/ 10mL) * 0.0020 M [SCN-]i = 4*10^-4 M Trial (#) 1 2 3 4 Concentration (M) 4.0*10^-4 6.0*10^-4 8.0*10^-4 0.001 3. Calculate the concentration of FeSCN2+ for equilibrium. [FeSCN2+]eq = (Aeq /Astd) * [FeSCN2+]std [FeSCN2+]eq = (0.135 / 1.063) * (2.0*10^-4) [FeSCN2+]eq = 2.540*10^-5 M Trial (#) Concentration (M) 1 2.540*10^-5 2 1.806*10^-5 3 3.706*10^-5 4 5.061*10^-5 4. Calculate the concentration of Fe3+ at equilibrium. [Fe3+]eq = ((Fe(NO3)3) mL / total mL) * (0.0020 M) Trial (#) 1 2 3 4 Concentration (M) 5. Calculate the concentration of SCN- at equilibrium. Trial (#) 1 2 3 4 Concentration (M) 6. Calculate Keq values for samples 1-4. Trial (#) 1 2 3 4 Keq 7. Using your four calculated Keq values, determine an average Keq value. How constant were your values? D. DISCUSSION Discuss results in terms of lecatlier’s principal. ...
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This note was uploaded on 04/21/2008 for the course CHEM 107 taught by Professor Generalchemforeng during the Fall '07 term at Texas A&M.

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