1. Equilibrium Constants Warm 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
[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

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