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Equilibrium Constants Warm Up Spec 20’s NOW!

Equilibrium Constants Warm Up Spec 20’s NOW!. First things first…. Turn on Spec 20’s to warm up Quiz Lab. Finding equilibrium constant Kc. SIMPLIFIED: [Fe] 3+ + [(NCS)] 1- ↔ [Fe(NCS)] 2+ + H 2 O. “ICE” Box – Finding the equilibrium concentration. Part A: Making Calibration Curve.

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Equilibrium Constants Warm Up Spec 20’s NOW!

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  1. Equilibrium ConstantsWarm Up Spec 20’s NOW!

  2. First things first… • Turn on Spec 20’s to warm up • Quiz • Lab

  3. Finding equilibrium constant Kc

  4. SIMPLIFIED: [Fe]3+ + [(NCS)]1- ↔ [Fe(NCS)]2+ + H2O

  5. “ICE” Box – Finding the equilibrium concentration

  6. Part A: Making Calibration Curve ***Note Change: You are not making the test tube solutions, it has been pre-made in the proper ratios. ***** For each test tube: Set Spec to 450 nm wavelength Blank the spec, using water solution (go to Crystal Violet Lab on how to blank spec) Now insert test tube with solution (1/2 full), record the %T

  7. Part B: Finding your sample conc Lab TA will assign you three test tubes Make the test tube solutions Blank the spec before finding the %T for each test tube solution

  8. End of class • Lab Clean up (check out by lab prep) • Turn in : • Lab notebook yellow carbon copies, pre-lab notebook copies, filled out data table

  9. Formal Lab • Typed hard copy by next week in class • Title Page, Data, Graph, Calculations, Discussion/Analysis, Reference

  10. Formal lab continue • Data table (via excel) • Calibration curve raw/analyzed data with columns: • Columns : (Test Tube #, Reagent Volumes, %T,Abs, [Fe(NCS)]2+ • Assigned Test Tube Raw Data Data With columns: • (Test Tube #, Reagent Volumes, %T, Abs, [Fe(NCS)]2+ • Assigned Test Tube Analyzed Data with columns • Test Tube #, Equilibrium Conc Fe3+, Equil Conc NCS-, Kc, Ave Kc for all tubes, and Stdev of Kc

  11. Calc Part 1: Finding Initial Conc • Part 1 Solve for calibration and assigned test tubes • Calcs A and B: Determine [Fe]3+ and [(NCS)1-] at the start (Initial Conc) • You made a solution so the concentration is diluted and thus DIFFERENT from bottle conc. MstockVstock = MsolnVsoln M1V1 = M2V2 • Where: V2 = Vtotalsoln = 7.00 mL

  12. Calibration curve graph • For your calibration curve data, you will make a graph of [Fe(NCS)]2+ vs. Absorbamce • The initial conc of Fe(NO3)3 = conc [Fe(NCS)]2+

  13. Part 2: Make Calibration Curve

  14. Part 2: Find reacted conc (Make calibration curve, get linear trendline) Solve for assigned test tubes Calc C: Determine[Fe(NCS)]2+ of unknowns • Use linear trendline to find equil [Fe(NCS)]2+ Calc D and E: Determine the reacted conc (Change Concentration) • [Fe]3+ and [(NCS)1-] reacted = equil [Fe(NCS)]2+

  15. Calc F and G: unreacted [Fe]3+ and [(NCS)1-] (Equilibrium Conc) • Calc A-D and B-E • Aka Conc beginning – Conc reacted • Calc H: Find Kc!! • Get ave Kc • Get stdev kc

  16. Conclusion • 1 page double spaced • Discuss the kc’s you got – precision/accuracy, trends • Discuss the graph – what you got and what it means • Error analysis

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