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**Equilibrium Constants Warm Up Spec 20’s NOW!**

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

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**Finding equilibrium constant Kc**

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

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**“ICE” Box – Finding the equilibrium concentration**

[Fe]3+ [(NCS)1- ] [Fe(NCS)]2+ Initial Conc M1V1 = M2V2 [A] [B] No product formed yet! Change of Conc -x (x is the limiting rgnt’s conc) -x +x Equil Conc [A]-x [B]-x

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**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

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**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

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**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

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**Formal Lab Typed hard copy by next week in class**

Title Page, Data, Graph, Calculations, Discussion/Analysis, Reference

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**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

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**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

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**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+

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**Part 2: Make Calibration Curve**

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**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+

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**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

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**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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