Chem 001 Lab Report Guidelines

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Chemistry

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Apr 3, 2024

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Chem 001 Lab Report Guidelines Fall 2023 A pre-lab is considered to be the Introduction, Procedures and Safety information for the lab. This usually includes a pre-lab question as well. A post lab is considered to be the data/results/observations recorded during the experiment, the calculations and graphs/spectra created after the lab is done and a conclusion (sometimes also called a discussion). The pre-lab and post-lab are called a lab report. For Chem 001 you will type 3 lab reports using the following guidelines. You do not have to include a safety section for Chem 001. A. Introduction : Provide background knowledge and concepts relevant to the experiment being performed. State the purpose and/or goal of the experiment. Include the method or technique that will be utilized. Include the chemicals that will be used during experimentation. Give a statement of expected results of the lab. Write in present tense, passive voice and third person. B. Procedure: This section includes a description of the procedures. It should provide enough detail for someone who is experienced to be able to reproduce your work. DO NOT REWRITE THE LAB MANUAL. Only include important steps that are critical to be able to perform the experiment. For example, you don’t need to include steps like putting on gloves or tarring a balance. The format of this section is up to you, for example a paragraph, drawings or numbered list. Write in present tense, passive voice and third person. C. Data/Results/Observations : Data, observations and results must be organized in tables. All measurements must include units. All results must include units. Data is any measurement or observation made during experimentation. Results are calculated values or spectral values. Calculated values must go into the data/results table. D. Calculations/Spectra/Graphs : Neatly and completely show your calculations. Significant figures are always graded. Don’t forget units in your calculations. All steps of a calculation must be shown. All spectra must be clearly labeled. All graphs must be clearly labeled. E. Conclusion : Begin by restating the purpose of the lab. Briefly describe the procedures, method or technique. State all relevant data or results that are most important to the findings and purpose of the lab. Relate the results/data of the lab back to the goal of the lab and assess the efficiency, precision or accuracy of the experiment. Give at least three possible sources of error of the experimentation. Error sources are not calculation or human based. Its best to think of error sources while actually performing the lab. Write in past tense, passive voice and third person. General rules: 1. Do not include pronouns such as I, we, our, my, the student, etc. This is what it means to write in third person. https://www.youtube.com/watch?v=pR9Sa_2Easo 2. Writing in present tense means you speak as if you haven’t yet done the lab. 3. Writing in past tense means you speak as if you’ve already completed the lab. 4. Write in a passive voice: https://www.youtube.com/watch?v=nRGLDD0BBdc (Remember do not use pronouns in a lab report)

Human Student CHEM-04B Ventura 03-07-2023 Lab 4: Synthesis of a Cobalt Compound Introduction: The goal of the lab is to synthesize a Cobalt Compound. A coordination compound otherwise known as a coordination complex usually consists of a central atom that is metallic. The ligand is attached to the central atom. The reaction of a Lewis acid (metal) and a Lewis base (ligand) will form a new complex that will have distinct chemical and physical properties. The substances that will be used for this lab are 10% ethylenediamine (en), 30% hydrogen peroxide, 12(M) HCl, cold methanol, and diethyl ether. There will also be recrystallization implemented in this lab to be able to get the final product of green crystals. Recrystallization is a purification technique where the Cobalt compound is mixed with a hot solvent to form a saturated solution. When the solution is cooling down, the solubility of the Cobalt compound decreases, and then pure crystals of the Cobalt compound [Co(en)2Cl₂]Cl will form. The end product is a Cobalt compound [Co(en)2Cl₂]Cl with ethylenediamine (en) attached to the Cobalt which will be red after dissolving with distilled water. Procedures: 1. Weight 12.0g of cobalt (II) chloride hexahydrate into a 250 mL Erlenmeyer flask. 2. Swirl to dissolve and add 25 mL of distilled water. 3. In the fume hood add 50 mL of 10% ethylenediamine (en) into the flask and swirl to mix. 4. Once it has dissolved add into the ice bath under 5 ℃ . 5. Add 10 mL of 30% hydrogen peroxide to the flask dropwise and swirl to mix. Leave the flask in the ice bath until hydrogen peroxide has been added. 6. Gently warm mixture to 60-70 ℃ . For about 10 minutes on the hot plate. 7. Remove the flask from the hot plate then add 45 mL of (12 M) HCl and swirl to mix. 8. Pour solution into a 400 or 600 mL beaker and boil to ⅓ of the original volume. Remove from heat and let it cool and the precipitate should be forming.

9. Weigh the filter paper and set up the vacuum filtration. 10. Filter the crystals by washing the solids twice with cold methanol and diethyl ether Data: Cobalt (II) hexahydrate 12.137g Distilled Water 25.00 mL 10% ethylenediamine (en) 50.01 mL 30% Hydrogen peroxide 10.00 mL (12M) HCl 45.00 mL 400 mL beaker 170.195 g Watch glass weight 64.287 g 2 filter paper weight .0569 g Filter paper + watch glass + [Co(en)2Cl₂]Cl mass 67.281 g [Co(en)2Cl₂]Cl final mass 2.425 g Theoretical yield 14.56 g % yield 16.66% Observation: 1. When the water was added to the cobalt (II) hexahydrate the liquid turned red after it dissolved. 2. Adding the ethylenediamine (en) the solution became dark/gray 3. When the peroxide was added the solution was bubbling up (exothermic) 4. No significant change when the solution was heating on the hot plate

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Calculations: [Co(en)2Cl₂]Cl Final mass 67.281-64.287–0.569=2.425 g CoCl₂* H₂O Molar mass 58.93+2(35.45)+6(18.01)=237.89 g/mol [Co(en)2Cl₂]Cl molar mass 58.93+2(60.1)+3(35.45)=285.48 g/mol Theoretical yield 12.137 g of CoCl₂*H₂O 1 mole of [Co(en)2Cl]Cl 1 mol of [Co(en)2Cl₂]Cl 285.48 g/mol of [Co(en)2Cl₂]Cl 237.89 g/mol CoCl₂*H₂O 1 mol of CoCl₂*H₂O 1 mol of CoCl₂*H₂O Conclusion: The main goal of this lab was to synthesize the Cobalt compound [Co(en)2Cl₂]Cl. The lab was done by chemical processes which started off with 12.137 grams of Cobalt (II) hexahydrate (CoCl₂*H₂O(S)). Then it was dissolved with distilled water and then added the ethylenediamine to the solution. Then there was 2 ethylenediamine with 2 H₂O around the Cobalt and which would make a trans-isomer of the Cobalt compound [Co(en)2H₂O]Cl. The ethylenediamine (en) replaces the H₂O which still has to be another chemical reaction to take off the rest of the H₂O. After the ethylenediamine (en) was added the solution was put into an ice bath to help precipitate form. This is when the H₂O is replaced by Cl because HCl was added and oxidized the cobalt with the help of the solution being on a hot plate after the HCl was added. Then the solution turned into the cobalt compound [Co(en)2Cl₂]Cl. Using the color wheel the Cobalt dissolved after distilled water was added was red. After having the ligand exchange and ethylenediamine replacing water the crystals turned green. As Ethylenediamine is a strong ligand and emits low energy the color emitted will be green the opposite of red which makes both of the hypotheses to be true. The final product being [Co(en)2H₂O]Cl and the color of the crystals emit green. The final mass of [Co(en)2H₂O]Cl was 2.425 grams. Then adding the mass of [Co(en)2H₂O]Cl (2.425) and CoCl₂* H₂O (12.137) will get 14.56 grams which is the theoretical yield. A % yield of 16.655% was determined. Errors that happened in the lab was having the hot plate go to more than 70 ℃ which increased the solubility more and would have less crystals in the solution. Some of the substance left behind and not go into the solution which messes up with the data table and the theoretical and % yield. When recording the weight of CoCl₂* H₂O some substance was outside of the flask which caused another mess up in the data table by the balance measuring the substance outside of the flask.