CHM243_Extraction

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Feb 20, 2024

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Experiment 3 Extraction

1 Introduction This experiment aimed to separate the mixture of naphthalene-benzoic acid using the technique of extraction. In order to yield pure compounds, this purification and separation process is dependent on the properties of the substances such as their melting point and their solubility in a specific solvent. 1 In this case, ethyl acetate possesses the ability to dissolve naphthalene and benzoic acid, establishing its efficacy as a solvent in the experiment. 2 To add, the low boiling point facilitates its removal from the mixture through evaporation, thereby enhancing the purification process for isolating the compounds of interest. The addition of an immiscible reagent, such as sodium hydroxide, assists in selectively partitioning the mixture into two distinct layers, aqueous and organic, making the extraction process possible. Figure 1. Mechanism from the lab manual 1 showing the separation of benzoic acid and naphthalene from the addition of insoluble sodium salt, forming the organic (naphthalene) and aqueous (benzoic acid) layer. Procedure 1.0g of naphthalene and 1.0g of benzoic acid were grinded together using a mortar and a pestle. The mixture was dissolved in 20 mL of ethyl acetate and placed in a separatory funnel. A 10 mL solution of cold 10% NaOH was added to the separatory funnel, shaken gently, and the cap was removed to release pressure. Once a clear separation of layers forms, with the funnel uncapped, the aqueous bottom layer was collected in a 100 mL beaker. Again, 10 mL of the NaOH solution

2 was introduced into the separatory funnel, gently shaken and the aqueous solution was collected in the same 100 mL beaker. By pouring from the top of the separatory funnel, the remaining organic layer was transferred in a 50 mL beaker. 10 mL of concentrated HCl was added dropwise to the aqueous layer until the benzoic acid stopped precipitation. The mixture was filtered by suction using a Buchner funnel to collect the benzoic acid. The product filtered was washed with 10 mL of ice-cold distilled water to dry. The mass and melting point were recorded. 1.0g of anhydrous sodium sulfate was added to the organic layer extracted and the mixture was left to stand for 5 minutes. An evaporating dish containing two boiling chips was weighed. The solution was then filtered by gravity filtration into the evaporating dish to remove the sodium sulfate salt. The beaker was rinsed with 3 mL of ethyl acetate and gravity filtered once again. The evaporating dish was placed on a steam bath for 15 minutes which allowed the formation of naphthalene crystals. The evaporating dish was weighed to determine the yield of the dried product.

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3 Results Table 1: Melting point and % yield for the initial mixture and pure compounds. Melting Point % Yield (95%) Initial mixture (naphthalene + benzoic acid) 56.2 - 107.7 ℃ N/A Pure benzoic acid 69.7 - 86.7 ℃ 100% 𝑎𝑐??𝑎𝑙 ?𝑒𝑖𝑔ℎ? ?ℎ𝑒𝑜𝑟𝑒?𝑖𝑐𝑎𝑙 ?𝑒𝑖𝑔ℎ? × 100% 0.769 𝑔 1.000 𝑔 ? 95/100 × = 80 % Pure naphthalene 112.3 - 124.2 ℃ 100% 1.283 𝑔 1.000 𝑔 ? 95/100 × = 1.35 % Discussion The extraction was successful, resulting in the formation of an aqueous layer (top) and an organic layer (bottom) which contained benzoic acid and naphthalene components, respectively. Further treatment and filtration of these liquids resulted in the production of white solids; 80% yield of pure benzoic acid and 135% of naphthalene were recorded. The melting point of a compound is presented in a range of values which helps to determine the efficiency of the separation technique. The crude melting point of the benzoic acid and naphthalene mixture was 56.2 ℃ - 107.7 ℃ which is a 51.5 ℃ difference range. However, following purification, the melting point of the pure benzoic acid was 69.7 - 86.7 ℃ whereas naphthalene held a melting point value of 112.3 - 124.2 ℃ . The initial broad melting point range is attributed to the presence of impurities within the compound and the narrower melting range observed indicates a higher level of purity 7 , affirming that the compound now exists in a homogenous state without admixture with other substances.

4 During the experiment, the separatory funnel containing the mixture was agitated to improve the separation of the liquid components. This agitation resulted in the accumulation of pressure within the funnel, as the solvent, ethyl acetate, evaporated and contributed to the initial ∼ 1 atmosphere of air pressure in the funnel. In order to alleviate this pressure, the funnel was opened regularly after shaking to release the accumulated pressure. Once two distinct layers were formed, and the bottom layer (containing benzoic acid) was discharged from the tip of the separatory funnel, the upper layer (containing naphthalene) had to be poured out from the top opening of the funnel. This precaution was taken to avoid any mixing of the organic layer with the previously drained aqueous layer. Also, to guarantee the thorough transfer and residue extraction of pure components, an additional precaution involving the rinsing of the beaker previously containing the naphthalene solution with 3 mL of ethyl acetate. The performance of this step and the second filtration of the solution in the beaker maximizes the yield by ensuring that all components, especially any adhering to the sides or the bottom of the beaker, are effectively transferred to the evaporation dish. When it comes to benzoic acid, the solids were washed with ice-cold water in order to reduce the solubility of the product, maintaining it in a solid state. 6 The process of washing the precipitates with ice-cold water also assists in the removal of additional impurities with high solubility that are present in the ethyl acetate solvent. Finally, to induce the formation of naphthalene crystals, the evaporating dish was placed on a steam bath with a temperature exceeding 77.1 ℃ (the boiling point of ethyl acetate). This elevated temperature facilitated the evaporation of the solvent from the mixture which led to the isolation of the naphthalene crystals.

5 In terms of errors, the reported yield of naphthalene, documented at 135%, surpasses the theoretical limit of 100%. This outcome is impossible and may stem from the lingering presence of impurities in the sample, potentially residual solvent like ethyl acetate. 8 Alternatively, a more valid explanation could be the addition of a piece of tape to the evaporating dish for reasons of identification before heating it in the steam bath. The failure to remove this tape before the final measurement may have contributed to the inflated yield. Although the piece of tape is small, its mass can exert a significant influence on the final weight of the pure compound since the initially utilized mass was of only 1.0g. In order to enhance the efficacy of this separation and purification technique, it is advisable to conduct multiple extractions. This approach reduces the quantity of material retained in the residue, thereby promoting a better extraction. 9 Additionally, employing smaller volumes of solvent is deemed more effective than a singular extraction. 10 With that being said, extraction is a frequently used purification and separation technique which is not only useful in chemistry labs, but also in the context of waste treatment, food engineering, pharmaceutical and hydrometallurgy. 11 Summary Table 2: Melting Point, mass and % yield of the pure benzoic acid and naphthalene compound. Pure compounds Melting Point Mass % Yield Benzoic Acid 69.7 - 86.7 ℃ 0.769 g 80% Naphthalene 112.3 - 124.2 ℃ 1.283 g 135%

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6 References 1. Beharry, A. Experiment 1, CHM243H5S Introductory Organic Chemistry II Course Manual, University of Toronto Mississauga, 2024 2. Li, Q. Yi, Z. Su, M. Sun, X. Solubility of Naphthalene in Isobutyl Acetate, n -Butyric Acid, Ethyl Acetate, N -Methyl Pyrrolidone, N , N -Dimethylformamide, and Tetrahydrofuran. https://pubs.acs.org/doi/10.1021/je800428r (accessed 2024-30-01) 3. SANLIFAN XIANG. Why is Ethyl Acetate a Good Solvent for Extraction https://www.slchemtech.com/news/why-is-ethyl-acetate-a-good-solvent-for-extraction.html (accessed 2024-30-01) 4. UCLA, Extraction (Part 1). https://www.chem.ucla.edu/~bacher/Specialtopics/extraction.html (accessed 2024-30-01) 5. LIBRETEXTS. Step-by-Step procedures for extraction. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Technique s_(Nichols)/04%3A_Extraction/4.06%3A_Step-by-Step_Procedures_For_Extractions (accessed 2024-31-01) 6. ONE PART OF CHEMISTRY. Recrystallization. https://1chemistry.blogspot.com/2011/08/recrystallization.html (accessed 2024-31-01)

7 7. Mettler Toledo. What is a Melting Point ? https://www.mt.com/ca/en/home/applications/Application_Browse_Laboratory_Analytics/Thermal _Values/melting-point-determination.html (accessed 2024-31-01) 8. LIBRETEXTS. Theoretical Yield and % Yield. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Introductory_Chemistry_(CK-1 2)/12%3A_Stoichiometry/12.09%3A_Theoretical_Yield_and_Percent_Yield#:~:text=However% 2C%20percent%20yields%20greater%20than,the%20products%20of%20the%20reaction . (accessed 2024-31-01) 9. LIBRETEXTS. Extraction Theory. https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Technique s_(Nichols)/04%3A_Extraction/4.05%3A_Extraction_Theory (accessed 2024-31-01) 10. Palleros, D. Liquid-Liquid Extraction. https://www.chem.tamu.edu/rgroup/gladysz/documents/extractions.pdf (accessed 2024-31-01) 11. Grow, C. Tan, M. Yeap, S. Chin, N. A Review on Extraction Techniques and Its Future Applications in Industry, European Journal of Lipid Science and Technology , 2021, 123(4).