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+ + H2O

“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

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

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

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

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

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

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

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+

Part 2: Make Calibration Curve

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+

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

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