6114 Chm 202 Lab 6 Equilibrium Rev 2 65 19 3 Absorbance Measurements To Determine The Equilibrium Constant 3 1 You Will 1 (68.36 KiB) Viewed 136 times
6114 Chm 202 Lab 6 Equilibrium Rev 2 65 19 3 Absorbance Measurements To Determine The Equilibrium Constant 3 1 You Will 2 (61.11 KiB) Viewed 136 times
6114 Chm 202 Lab 6 Equilibrium Rev 2 65 19 3 Absorbance Measurements To Determine The Equilibrium Constant 3 1 You Will 3 (34.89 KiB) Viewed 136 times
6114 Chm 202 Lab 6 Equilibrium Rev 2 65 19 3 Absorbance Measurements To Determine The Equilibrium Constant 3 1 You Will 4 (41.22 KiB) Viewed 136 times
6114 CHM-202 Lab 6 Equilibrium Rev 2 65-19 3. Absorbance measurements to determine the Equilibrium Constant 3.1 You will perform this portion of the experiment with 0.0025M Fe(NO) and KSCN solutions Do not use the concentrated KSCN (IM) or diluted Fe(NO) 3.2 Prepare the solutions described in the table below. You may find it convenient to prepare halfer the solutions and measure the absorbance and then prepare the rest of the solutions. We will stay numbering with test tube 10 in order to ensure that the equilibrium constant data is kept separate from the Beer's Law data. Test Tube Number 10 11 12 13 14 15 16 17 18 19 0.0025 M Fe(NO3)2 ml 1.0 1.0 1.0 2.0 2.0 2.0 2.0 2.0 0.0025 M KSCN mL 1.0 2.0 3.0 1.0 1.5 2.0 2.5 3.0 1.0 2.0 0.1 M HNO, mL 5.0 4.0 3.0 4.0 3.5 3.0 2.5 2.0 3.0 2.0 on mielenils olol 3.0 3.0 3.3 Measure the absorbance (not transmittance) of each solution using the spectrophotometer provided at the lambda max measured in 2.8 and record this data in the space provided. Be sure to rinse the cuvette (test tube in the spectrophotometer) with 1-2 mL of solution prior to measuring the absorbance. 4. Calculation of the Equilibrium Constant ko Note: The calculations below can be performed manually or using a spreadsheet computer program such as MS excel. If you use a spreadsheet program indicate using one set of data (one test tube number) how the values were calculated. It will save you time if you calculate the initial concentrations of iron ion for all test tubes and the initial concentrations of thiocyanate ion for test tubes 10-19 prior to the laboratory session. Calculate the initial Fe" and SCN concentrations for test tubes 10-19 using the concentration of the reagents used (0.0025M) and their subsequent dilution. For example the Fe concentration in test tube 10 is (0.0025M)*(1.0 mLy(7.0mL). Record these values in the table provided. 4.2 Calculate the equilibrium concentration of the Fe(SCN) - complex using the absorbance at lambda max nm (A at Amm) for each test tube and the slope determined from the Beer's Law analysis. Use the equation below to solve for the equilibrium concentration of the complex (FeSCN* Jeq). 4.1 A at an = ebe = (cb) [Fe(SCN)" Jeq - (slope)[Fe(SCN)?leq
CHM-202 Lab 6 Equilibrium Rev 2 G5-19 43 . 7/14 The iron ion (Fe) can exist in one of two forms in solution: as the free ion and as the Fe(SCN) complex. As a result the sum of the free ion and the complex must equal the total amount of iron present which is the initial iron concentration calculated in 4.1. Therefore it must be true that the iron present as the free ion can be calculated as follows: [Fe Jeq = [Fe') initial - [Fe(SCN)? Jeq = Total Fe" - complexed Fe Use this information to calculate the free iron ion present at equilibrium ([Fe3+ Jeq)for test tubes 10-19 and enter this information into the table provided. relationship is true for the thiocyanate ion. Calculate the equilibrium concentration of the thiocyanate ion [SCN- Jeq) for test tubes 10-19 and enter this information into the table The same 4.4 provided. 4.5 [SCN" Jeq = [SCN') initial - [Fe(SCN)?" Jeq = Total SCN - complexed SCN You now have values for all of the species present in the equilibrium: iron ion, thiocyanate ion, and the complex. Calculate the equilibrium constant for test tubes 10-19 from the equilibrium constant expression. Kc = [Fe(SCN)? Jeg [Fe" Jeq [SCN Jeq Record the values obtained in the table provided and calculate the average value for all the Ko values obtained. Record this average value in the table provided.
CHM 202 Lab 6 Equilibrium Rev 2 G5-19 3. Absorbance measurements to determine the Equilibrium Constant 19.133.86MY Slope of Beer's Law Plot from previous page [Fe(SCN)) A at Test Tube Number 10 0.175 11 0.276 12 0.396 13 0.346 14 0.377 15 0.482 16 0.624 17 0.664 18 0.364 19 0.676
11/14 CM22 Lab 6 Equilibrium Rev 2 G5-19 Calculation of the Equilibrium Constant K Initial [Fe' A at may Initial (SCN) Test Tube Equil [Fe(CN)") Equil [Fe Equil (SCN) K K Number 10 11 12 13 14 15 16 17 18 19 Average value for Kc =
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