Lab 7: Spectro Chemical Series Background and Procedure

CHEM& 163 –Zijlstra – Summer 2026 Lab 7 Background/Procedure Lab 7. Coordination Chemistry - Synthesis and Spectroscopy Background & Procedure Pre-Lab Assignment ❑ Read this entire handout, watch the video on filtrations and review the Ch. 21 slides in this week’s Canvas module ❑ Prepare your notebook: ▪ Table of contents ▪ Lab header ▪ Intro/purpose statement (including ALL equations and spectrochemical series) ▪ Draw the data tables (with descriptive titles!) that you will be completing during the lab make sure to include space for observations and calculations ▪ You do NOT need to provide a flow chart, you can use the provided instructions or this lab directly. ❑ Complete the pre-lab questions posted on Canvas (electronically or directly in your notebook) ❑ Submit a single scan of your pre-lab questions to the pre-lab 7 assignment ─ Due by 11:59pm night before lab Lab Activity On lab day: ❑ Attend the in-person lab session. ❑ Bring your goggles, calculator, pen, and prepped notebook ❑ Do the experiment. ❑ Fill in your data and calculated results, writing directly in your lab notebook. ❑ Have your instructor’s initial approval of your data at the end of the lab period. ❑ Submit a single pdf of your notebook pages to the In-Lab 7 assignment found in Canvas. ─ Due by 11:59p on the day of your lab. Post-Lab Assignment ❑ Do the Post-Lab Report, completing the calculations, tables, and analysis questions and writing a brief discussion as described in the Lab 7 Post-Lab Report handout. ❑ Submit a single pdf (scan or convert the word document) of your entire Report to the Post-Lab 7 assignment. ─ Due by 11:59p on Aug 26th. CHEM& 163 –Zijlstra – Summer 2026 Lab 7 Background/Procedure Knowledge and Skills This laboratory exercise will provide experience to further your understanding of the following concepts: • • • Coordination complexes Spectrochemical series Spectrophotometry After you complete this laboratory exercise, you will be able to: • Set up and perform gravitational and vacuum filtrations • Apply spectrophotometric techniques to determine λmax • Use λmax to calculate energy differences and validate the spectrochemical series Background Transition metal complexes often have bright and vivid colors, that originate from d-d electron transitions. Crystal field theory allows us to explain this phenomena through dorbital splitting. In CHEM&162 we treated all d-orbitals as degenerate (having the same energy), this is true in a “free” metal ion but when ligands (ion, atoms, or molecule that attaches to the metal ion) they change the relative energy of the d-orbital depending on their orientation. Depending on the number of ligands and coordination number different geometrical arrangements around the central metal ion occur. • • • 6-coordinate complexes are octahedral. 5-coordinate complexes are trigonal bipyramidal or square planar depending on the nature of the ligand. 4-coordinate complexes are tetrahedral or square planar. d8 and d9 complexes favor square planar geometry whereas all others favor tetrahedral geometry. An example of an octahedral coordination compound if [Co(NH3)5Cl]Cl2. Cobalt is surrounded by six ligands, 5 NH3s and 1 Cl, forms a complex ion, [Co(NH3)5Cl]2+ and it’s overall +2 charge is balanced out by 2 Cl- counter ions. We know that NH3 is neutral and Cl has a – 1 charge, as there are also two Cl- counter ions the metal must have a +3 charge. Depending on the geometry around the metal the ligand field changes and the d-orbitals are split up. This splitting explains spectral and magnetic properties that cannot be explained using Hund’s rule and the Aufbau principle. The magnitude of the ΔE between groups of degenerate d-orbitals depends on the following: CHEM& 163 –Zijlstra – Summer 2026 Lab 7 Background/Procedure 1. The strength of the ligands attached to the metal ion 2. The charge of the metal ion 3. The geometry of the complex ion In this lab we will be investigating the relative strength of ligands attached to the same type of metal ion. As the charge on the metal increases ligands are drawn closer to the metal and the ΔE increases due to increased electron repulsions. The effect of geometry on the magnitude of orbital splitting can be seen when comparing the splitting diagrams shown in figure 1. This effect is dependent upon the proximity of the d orbitals to the ligand point charges and the effect of electron repulsion. Figure 1. d-orbital splitting diagrams in common geometries. One way to measure ΔE of the split d-orbitals is to promote an electron from a lower energy level to a higher one. This can be done by shining a light on the sample and observing the absorbance spectrum to check which wavelengths of lights are absorbed. Figure 2. Excitation of a d-electron from the ground into the excited state (shown for octahedral d-orbital splitting). In this lab we will be determining the ΔE for a number of copper complexes by measuring the absorbance spectrum and determining the λmax. As part of the post-lab you will calculate the ΔE, using ΔE = hc/λ. CHEM& 163 –Zijlstra – Summer 2026 Lab 7 Background/Procedure Procedure Work in pairs for this experiment. The complex prepared in part A needs about 45 min. to react. Move onto the 2nd part while the reaction is proceeding to complete the whole lab. Part A 1. Weigh 0.5 g of copper (II) sulfate pentahydrate and place it into a 100 mL beaker. Record the exact mass in table 1. 2. Add 3 mL of 1M HCl to your beaker to dissolve the copper complex 3. Add 0.25 g of glycine, NH2CH2CO2H, to the solution. Record the exact mass of glycine used in table 1. 4. Prepare a water bath by placing a clay pipe triangle in a crystallization dish and filling the dish half full of tap water. 5. Warm the water bath on a hotplate and place your beaker containing the solution in the water bath so that it rests on the triangle. 6. Warm the solution for 45 minutes on the hot plate – make sure the water is not boiling- proceed with Part B. 7. Add sodium bicarbonate, NaHCO3, in small portions (dropwise). Slowly keep adding NaHCO3 until no more CO2 is released. A blue precipitate should form. 8. Obtain 125 mL filtration flask + funnel and set up your vacuum filtration 9. Obtain a piece of filter paper, label it and weight it. Record the weight in table 1. 10. Turn on the vacuum and filter you reaction mixture, using a rubber policeman to scrape content onto the filter as needed. 11. Let the vacuum run for a few minutes after filtration to ensure the solid sample is dry 12. Carefully weigh the filter paper and note the weight in Table 1. 13. Transfer solid material in a 100 mL beaker, add 20 mL of deionized water, and filter the solution to remove any remaining solids. 14. Transfer the some of the solution to your cuvette and record the λ max for the Cu(gly)2·H2O solution. Part B **for all absorbance spectra – if more than 1 peak appears note the λmax with the highest wavelength** 1. Obtain 10 mL of 0.1 M copper (II) sulfate solution from the stock bottle 2. Obtain a spectrophotometer and connect it to the computer via USB (use the USB ports in the computer don’t use the port in the screen). 3. Open spectral analysis and open an abs. vs. wavelength experiment. 4. Fill your cuvette with deionized water, insert it into the photometer and click “finish calibration”. 5. Empty your cuvette and transfer 1 mL of 0.1 M copper (II) sulfate into your cuvette using a disposable pipette. Add 2 mL of DI water and use the pipette to mix the solution in the cuvette. 6. Load your cuvette in the spectrophotomer and press collect. Click the graph botton and go to view statistics to obtain your λmax. Record this value in table 2. Rinse your cuvette with deionized water after usage. CHEM& 163 –Zijlstra – Summer 2026 Lab 7 Background/Procedure 7. Using a graduated cylinder measure 5 mL of copper (II) and transfer to a large test tube. Add 10 mL of water and 2g of solid NaCl. Stopper the tube and vortex thoroughly. 8. Transfer your solution to the cuvette and take an absorbance spectrum by pressing collect. Record its λmax in table 2 (if absorbance is higher than 2 dilute your sample and run again). Rinse your cuvette with DI water after usage. 9. Use a graduated cylinder to measure 5 mL of the complex prepared in step 7 and transfer it to a clean test tube. Transfer your test tube to the hood and add 1 mL of NH4OH. A precipitate might initially form, still your solution until everything is dissolved (add more NH4OH if needed). 10. Transfer your solution to the cuvette and take an absorbance spectrum by pressing collect. Record its λmax in table 2 (if absorbance is higher than 2 dilute your sample and run again). Rinse your cuvette with DI water after usage. 11. Finish part A and transfer that solution to the cuvette and take an absorbance spectrum by pressing collect. Record its λmax in table 2 (if absorbance is higher than 2 dilute your sample and run again). Rinse your cuvette with DI water after usage. Table 1. Mass of CuSO4·5H2O (g) Mass of glycine (g) Mass of Cu(gly)2·H2O (g) Table 2. Compound λmax This lab is adapted from the UW spectrochemical series lab.