Jason Stackhouse Chemistry 151L Experiment 1

OVERALL 25/100 PRESENTATION: 0/10 Grammar and sentence structure really needs to be improved I stopped grading your intro because it was extremely poorly written. You need to redo your intro for the next report. Also, see me 11am on Monday in my office (PSB 253) to discuss your report. You also didnt answer the questions on the handout. Synthesis of Hexamminecobalt(III) Chloride
Abstract The Synthesis of hexamminecobalt(III) Chloride with Cobalt(II) Chloride requires the oxidation of Cobalt metal in order to be able to add as many ammonia ligands needed for the
Comment [YA2]: Awkward sentence Comment [YA1]: 2/10 Your statements are redundant and dont clearly state what is going on in the experiment. You are missing important results! Formatted: Justified

hexammines to bond on cobalt. This process is a strong example of crystal field theory and dorbital splitting energy. In this experiment the crystal field theory will be applied using charcoal
Comment [YA3]: No possessives!

as a physical catalysts for the oxidation of cobalt. With applied heat we will be able to yield hexamminecobalt(III) Chloride. Introduction The preparation of cobalt(III) would be normally hard to find in nature because cobalt(III) easily reduces to cobalt(II) when put in contact with other negative ions. By occupying all free orbitals with ammonia and balancing the charge with chloride ions, cobalt(III)
Comment [YA4]: 11/25 I dont think you understand the theory at all. You need to see me. Comment [YA5]: How does nature prepare cobalt 3? Comment [YA6]: Reference?

Comment [YA7]: colloquial

can be solidified after oxidation. But ammonia does more than just occupy the free electrons in cobalt(III)s orbitals, as stated by the crystal field theory nitrogen helps keep the orbital electrons in the ground valence band. Cobalt(II) and (III) both should be paramagnetic because both of them have unpaired electrons in their atomic orbitals. Crystal field theory explains how metal electrons are able to occupy different high spin and low spin configurations depending on the band gap energy between the conduction and valence bands. This only applies to d orbital elements because in the d-orbital the five atomic orbitals usually split into high spin (2 orbitals) and low spin (3 orbitals) orbitals. As electrons fill the atomic orbitals, normally electrons would fill each atomic orbital with one electron first,
Comment [YA13]: Run-on sentence Comment [YA8]: this information came out of nowhere. You need to transition into this material. Comment [YA9]: This is incorrect. This needed to be in the discussion as well. Deleted: Crystal Field Theory Comment [YA10]: This is not band theory! Band theory is used for electronics Comment [YA11]: What? Comment [YA12]: Nope. This is completely incorrect

high spin and low spin included, then start to double up with opposite spins. . But as the d orbitals split, the electrons have to compete against the band gap energy to occupy the higher atomic orbitals. When the band energy becomes higher than the energy it takes to fill a low spin orbital with two electrons, electrons will begin to double up on the low spin atomic orbitals instead of jumping to the high spin orbitals. The band gap energy begins to increase as a metal gets oxidized and gains a higher positive charge. Ligands may also increase band gap energy by creating a strong field and a more covalent bond. Ligands with lower electronegativity such as ammonia, cyanide, carbon monoxide, and water are good ligands for increasing band gap energy between high spin and low spin configurations. In this experiment the starting reagent is cobalt(II) chloride hexahydrate, which is a lower oxidation state cobalt with water as the ligands and two chlorides to balance out the charge. By oxidizing the cobalt(II) to cobalt(III) in air under heat and adding stronger ligands to the cobalt, cobalts orbital split gap energy is significantly increased making it more

Comment [YA14]: Dont start sentence with but Deleted: This is the normal electronic configurations for s and p orbitals Deleted: s Deleted: high spin

Comment [YA15]: This is a bad sentence. Comment [YA16]: We didnt heat it Deleted: a

energetically favorable for the electrons to double up in a low spin configuration rather than overcome the energy gap to occupy a high spin configuration. The product with the stronger field ligand, ammonia, is hexamine cobalt(III) chloride.

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The mechanism for reaction is physically catalyzed by charcoal. Cobalt(II) chloride hexahydrate substitutes five of its six waters for ammonia during the heating process but
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requires extra energy for the addition of the last ammonia. Two cobalt ions are caught in the charcoal active site and form a peroxo-bridge . During this time the bond between cobalt and the peroxo-bridge is weaker allowing for ammonia to attack the cobalt and reduce the cobalt(II)

Deleted: a Deleted: n Deleted: with its remaining H2O ligands

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to cobalt(III).
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The color of Cobalt(III) should be reddish in color because its absorbance wavelength is
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around that of 440 to 490 nanometers. This means that Cobalt(III) absorbs blue light and
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transmits red light giving it a red color. On the UV-Vis spectra of Cobalt(III) we should see a peaks over the region of 420-490 nanometers. Experimental For my procedure I used a handout from the chemistry 151 lab class experiment 1.

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Comment [YA20]: 7/10 Color of product? Note that you got the IR from us. Also reference the handout.

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Instead of analyzing the product with IR and there was no time to complete those spectroscopy at the end of the experiment so only percent yield was collected. The end drying process lasted over a span of 24 hours to obtain the best drying results. Results and Discussion
Comment [YA21]: 0/25 You didnt mention IR at all!

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Hexammine cobalt(III) chloride resulted from the reaction catalyzed by charcoal. After filtering out the charcoal and leaving time to crystallize, an orange powder is what resulted
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from the experiment. . Table 1: The starting reagents and ending products amounts from the synthesis of hexamine cobalt(III) chloride.
Reagent Cobalt(II) Chloride Hexahydate Amonium Chloride Amonia Product Initial 4.79 grams 3.27 grams 10 ml Final 2.29 grams Orange with green spots Color Violet White colorless

Deleted: Though the powder is not ideal when trying solidify the crystal cobalt(III) structure, we had a good color to talk about Comment [YA24]: this goes in the appendix

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Hexamminecobalt(III) Chloride

Comment [YA23]: sweet dr seuss material

We see from this table that the initial color of the Cobalt(II) was blue/violet. This is because as the electrons were absorbed by the cobalt(II) the electrons in the low spin level would jump to the already occupied high spin level and leave a low spin level empty, absorbing high wavelengths around 550-700 nanometers and reflecting back the blue/violet color. But when the cobalt(II) becomes oxidized to cobalt(III) the excitation of electrons to the high spin orbital does not leave an empty low spin orbital behind because they were already double electron filled orbitals to begin with. This causes cobalt(III) to absorb shorter wavelengths around 400 to 500 nanometers and transmit back a orange color. In this experiment it is interesting to find green spots on the hexamine cobalt(III) chloride after the long process of dehydrating it. This is no doubt due to the hexamine cobalt(III) chloride reducing back to cobalt(II) giving it a more blue spectrum side color and absorbing higher wavelength lights. cobalt and other metals like
Comment [YA26]: there is some doubt to this. Dont take everything at face value Deleted: As I said before, Comment [YA25]: this doesnt mean anything to me Deleted: reflect

to stay at a lower oxidation state because it is more energetically favorable for electrons to be spread out on the metal atom rather than concentrated and doubled up on single atomic orbitals. The issue most likely had to do with either the last step of the mechanism (adding on the last ammonia) or the chlorination of hexamine cobalt(III). If the six ammonias are not properly added onto the cobalt then cobalt(II) cannot oxidize to cobalt(III) in the last step of the mechanism involving the charcoal catalyst. Perhaps the charcoal was not properly dissolved in the solution . Cobalt(II) chloride is the limiting reagent with the amounts given so there is no question about amount put in but perhaps it was not stirred enough. Lastly, due to the low boiling point of ammonia, a good reason why cobalt could have stayed in its reduced cobalt(II) form is because during the heating process too much ammonia was boiled out of the solution. This would leave cobalt(II) not enough ammonia to bind to in order to get oxidized in the last mechanism step. Table 2: calculation for percent yield.
Theoretical Yeild Actual Yeild 5.37 grams 2.30 grams
Deleted: yielded Comment [YA31]: Redundant with table. This is also a bad sentence. Comment [YA28]: Charcoal doesnt dissolve Deleted: while heating Deleted: The second reason is if the hexamine cobalt(III) chloride did not properly chlorinate, then that would leave a positive charge on the rest of the molecule causing cobalt to want to reduce back down to cobalt(II) in order to balance out the resulting positive charge. The problem could have stemmed from a lack of ammonium chloride dissolved into the solution. Comment [YA29]: If it dissolved, then it stirred enough Comment [YA30]: This is true, good! Yet this doesnt explain why your originally orange product produced green spots after drying in the oven for a week. Deleted: The table below shows the Comment [YA27]: NO. Chlorine only crystallizes out your product by being the counter ion.

Percent Yeild 42.80% The resulting percent yield of the experiment for hexamine cobalt(III) chloride was 42.8 percent from the theoretical yield of 5.37grams using cobalt(II) chloride as the limiting reagent. This result is not ideal from the reaction because it means that the other fifty percent of the products were either lost filtration or was not created to product. Though the low yield of product, our results were still enough to explain and show that the crystal field theory was upheld in the reaction showed by the color changed and reversion of color change back to green. Conclusion

Comment [YA32]: Avoid the word create Comment [YA33]: It was never green to begin with Comment [YA34]: 5/10 This is very similar to the last paragraph, and what you said in the beginning of the introduction. This section is meant for your thoughts as to how the experiment could have been improved. Then finish by tying in all the concepts together.

The oxidation of cobalt(II) to cobalt(III) was successfully shown in this experiment by the color change of the cobalt based products to an orange color from the normal blue/violet color that a reduced cobalt(II) shows. This proves that crystal field theory was upheld in the oxidation of cobalt(II) to cobalt(III) because as the electrons stayed in the lower energy state the absorption of color changed from red absorption to blue absorption. This oxidation was done by adding strong field ligands and oxidizing the cobalt from cobalt(II) to cobalt(III).
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References 1) Oliver, S. Experiment 1) Synthesis of Hexamine Cobalt(III) Chloride, 2012, Chemistry Department, University of California Santa Cruz, http://www.chem.ucsc.edu/~soliver/151L/ 2) Bjerrum, J.;McReynolds, J.P. Inorg. Synthesis,1946, 2,216-221 (in library reference section, bt a scanned copy is provided on http://www.chem.ucsc.edu/~soliver/151L/)

Comment [YA36]: 0/10 Not enough references No calculations No IR