4-2b. In-Lab Assignment Transition Metal Synthesis - Week 2 PDF

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Transition Metal Synthesis - Week 2 In-Lab Assignment

Note: Although it was not discussed in class, the nickel octahedral complexes you will be studying have 3 spin-allowed transitions. We are focusing on the middle band that falls in the visible region. In the water complex, the first band that is typically in the UV may fall at the tail end of the visible region, but you do not need to record that peak. The third and highest wavelength band is in the IR, you may notice the beginning of this peak in your spectra. Data Use this space to record all data in an organized fashion for the addition of ligands to the nickel-water complex. Be sure to include specific color observations. You should have 7 wavelengths (1 for nickel-water, 3 for the phenanthroline (phen) ligand, and 3 for the ethylenediamine (en) ligand). 50 mL of a 0.100 M NiCl2 solution M = mol/L 0.100M NiCl = x mol/0.050L x = 0.005 mol MM NiCl = 237.72 g/mol Grams of NiCl = 237.72 * 0.005 mol = 1.189 g NiCl2 (also actual measured value) mL of en: 20.00 mL mL of phen: 20.00 mL 5.00 mL of [Ni(OH2)6]2+ complex for both en and phen starting solution Table 1. Wavelength and color change with addition of en mL of en added Color of complex 0.00 Green 1.00 Light blue-green 2.00 Blue 3.00 Blue 4.00 Blue 5.00 Blue 6.00 Blue-purple 7.00 purple 8.00 purple 9.00 purple 10.00 purple Table 2. Wavelength and color change with addition of phen mL of en added Color of complex 0.00 Green 1.00 blue-green 2.00 Blue 3.00 Blue 4.00 Blue-purple

Max wavelength (nm) 660.9

624.5

571.1

555.6

Max wavelength 660.9

579.6

5.00 6.00 7.00 8.00 9.00 10.00

purple purple Purple-pink pink pink pink

564.9

525.3

In-Lab Questions 1. What is the maximum wavelength observed for the nickel-water [Ni(OH 2)6]2+ complex? The max wavelength for the complex was 660.9 nm at the peak we were particularly looking at with an absorbance value of 0.185 2. After the full addition of each ligand, you should have observed a pink or purple color. Complete the chart below. Ligand

λmax (nm)

Formula of Complex

phen

525.3

[Ni(phen)3]2+

en

555.6

[Ni(en)3]2+

3. How many d electrons does Ni2+ have? Ni2+ has 8 d electrons 4. What type of transition is responsible for the colors in these complexes? d-d transitions are responsible for the color changes in these complexes. This is because they contain unfilled d-split orbitals 5. Using your data above, draw conclusions about the d-splitting for each ligand (H 2O, en, phen). Order the complexes from least to greatest d-splitting, and discuss the reason for your ordering. In order from least to greatest d-splitting: H 2O, en, then phen. This means that phen creates the largest d-splitting when bonded to the metal ion, while water creates the weakest d-splitting observed when bonded to metal. This is backed up by our data since water absorbs light of higher energy than phen was. This gave the complex a green appearance with water, while the en and phen complexes appeared purple and pink respectively because the complex was absorbing lower energy photons in the red section of the spectrum and transmitting electrons in purple end of spectrum. En was found to be weaker than phen since 2 chelated phen transmitted the same color as 3 chelated en....