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Author: Talesha Doucette Reviewer: Loryn Johnson Editor: Mya Thompkins Organic Chem Lab1 Group 9 Acid Base Liquid-Liquid Extraction Lead Introduction: When performing acid base liquid-liquid extractions, one’s goal is to separate a mixture of organic compounds into individual compounds or smaller compounds. There are three concepts this procedure relies on to perform its targeted tasks: intermolecular forces of molecules, their polarity, and the idea of like dissolves like. Each concept relates to one another. When a compound is polar, it’s more likely to dissolve in a polar solution. If it is non-polar, it is more likely to dissolve in a non-polar solution. It is also possible for a compound to be partially polar and non-polar, and this is where intermolecular forces come into place. Sometimes, a compound displaying both polar and non-polar qualities can lean more towards one or the other. This would still cause the compound to just be considered polar or non-polar, even when it is both. During acid base liquid-liquid extraction, a definite aqueous layer and organic layer are formed from the two solvents being added into the separatory funnel. The separatory funnel allows for the extraction of one liquid, the bottom layer. To form two layers, it is important for the two solvents to have a different polarity from one another so that they will separate instead of mix. Another important factor to consider when performing acid base liquid-liquid extraction is density. When the two layers are separated in the separatory funnel, the location of the two solvents will be determined by their densities. A denser solvent will rest at the bottom, while the less dense solvent will be at the top. It is common in organic chemistry reactions that in a mixture of multiple organic compounds, they all have a neutral charge and have large non-polar sections. As a result, these compounds are likely to dissolve in non-polar solvent. If the molecules in the compound can act as a BronstedLowry base, a proton acceptor, a Bronsted-Lowry acid, or proton donator, then acid base liquidliquid extraction can be used to separate the mixture. During an acid base reaction, the charge of a Bronsted-Lowry acid becomes more negative, and the charge of a Bronsted-Lowry base becomes more positive. As a result, the compound becomes more polar allowing it to dissolve in more polar, aqueous solvent. It is very important in acid base liquid-liquid extractions to identify the basic or acidic locations in a target molecule. A Bronsted-Lowry acid would be used to protonate a molecule, making it more positive, when a basic site exists. This will cause the molecule to be more soluble in the aqueous polar phase. A Bronsted-Lowry base would be used in the presence of an acidic site causing the removal of a proton. This will cause the molecule to become more soluble in the aqueous polar phase. If a compound is considered neutral and cannot act as a Bronsted-Lowry acid or base, then that compound will remain in the non-polar phase. Following such extractions, a compound may then need to be isolated. This process is completed by neutralizing the aqueous phase. In the case that a Bronsted-Lowry base becomes more positive due to the protonation of the molecule, a Bronsted-Lowry base would be added to neutralize it and return it to its non-polar state. When a Bronsted-Lowry acid becomes more negatively charged, a Bronsted-Lowry acid can be added to neutralize the molecule and return it to its non-polar state. This will cause the compound to separate from an aqueous solution and become isolated.

Once the molecule is neutralized and isolated, it is necessary to ‘dry’ the molecule using a drying agent, so the remaining water does not taint the compound. A drying agent will be added to remove any water residing in the solvent. Drying agent must be added until there are no more clumps at the bottom of the flask. Once drying is completed, evaporation of the organic solvent is performed leaving the preferred compound. In this lab, a mixture was assigned (igure 1). In the mixture, one compound was neutral, while the other was acidic or basic. The structures below were to be observed to determine which compound is the Bronsted-Lowry acid or base, and which is the neutral compound. 1M HCL and 1M NaOH were provided to perform the proper Bronsted-Lowry acid base reaction. It was also important to determine whether the non-neutral compound was an acid or base. This would determine which aqueous solution would be used, 1M NaOH or 1M HCL, to perform the acidbase reaction and determine the protonation state.

Figure 1: Given Compound Mixture Compound

Melting Point (In Celsius) 88-90

Molar Mass (g/mol)

Boiling Point (In Celsius)

165.192

310

55-58

195.083

182

Figure 2: Physical Properties of Compounds The percent yield calculates the amount of a reactant used and successfully transferred into a product. Eq.1 Percent yield= (actual yield/theoretical yield) x100%

Experimental: 15.0 mL of the assigned mixture was obtained and placed into a 125 mL separatory funnel. The compound was then extracted three times with 10 mL of the aqueous solution, 1M HCL. To complete the extraction, using one hand, the stopper was held in place and the separatory funnel was inverted and swirled. The funnel was then vented to release pressure by inverting the funnel and keeping the stopper held in place. The stopcock faced away from all students going upward into the hood. The stopcock was closed, and the process was repeated several times. Once the inverting was completed, an iron ring was secured onto a stand and the funnel was securely placed into the ring. In order to ensure the mixture was separated completely, the separatory funnel was allowed a few minutes to sit. Next, a clean 200mL beaker was placed below the funnel. The stopper was removed, the stopcock was opened, and the bottom layer was slowly drained into the beaker. Once the bottom layer was nearly removed, the draining rate was slowed and then stopped once all the bottom layer was completely in the beaker. Once the extraction was completed, the compound was neutralized by HCL. HCl was slowly added into the beaker. After adding HCl each time, litmus paper was used to check the acidity of the solution and determine when it became neutral. After neutrality was accomplished, HCl was continuously added until the solution became acidic. The litmus paper was continuously used during this time. In doing so, a solid formed at the bottom of the beaker remaining undissolved in solution. The solid was then isolated through suction filtration. The solid was continuously dried for a few minutes while air was pulled through the function. Once it was complete, the solid was transferred to a watch glass and weighed at .096 g. Next, the organic, diethyl ether solution was dried through the addition of anhydrous sodium sulfate. It is important to note that drying a compound simply refers to the removal of water in a compound, the liquid form of the compound will remain. In order to dry the organic layer, the diethyl ether solution was added to a 50 mL Erlenmeyer flask. The solution was then dried through the addition of sodium sulfate, only adding a little at a time. The sodium sulfate began to clump indicating water was being removed. The sodium sulfate was continuously added until the clumps began to flow freely at the bottom of the flask whenever it was swirled. It was then confirmed that enough sodium sulfate was added by the lab TA. The liquid in the flask was then transferred to a 50 mL beaker while the sodium sulfate remained in the flask. A water bath was then heated to 40-50 degrees Celsius. The beaker containing the ether solution was then heated in the hot water bath until the liquid was completely removed. Due to no solid forming at the bottom of the beaker, the beaker containing the diethyl ether solution was then placed into an ice bath to stimulate the formation of a solid. Once the solid was formed, it was transferred onto a watch glass and weighed at .085 g. The melting point of the solids was then determined. Results and Calculations: Using the knowledge obtained from the Bronsted-Lowry theory, it was determined in the beginning that the mixture given (Figure 1) contained a base along with the neutral component. Once the HCl was added into the separatory funnel, it rested at the bottom while the diethyl ether rested at the top. This concluded the aqueous layer was the HCl, and the organic layer was the diethyl ether. Once the first solid was formed it was weighed on a watch glass. The weight of the solid was recorded as .096g (Figure 3). Once the second solid was formed, it was then weighed on a watch glass. Its recorded weight was .085g (Figure 4). Once the weight of both solids was recorded, Eq. 1 was used to calculate the percent yield. The percent yield was recorded as 89%. After the percent yield was calculated, the melting point of both solids were obtained. The melting points given in Figure 2 helped to determine the accuracy of the two solids’ melting

points. The first solid’s melting point was recorded as 89 degrees Celsius. The second solid’s melting point was determined as 56 degrees Celsius.

Figure 3: First solid weighed

Figure 4: Second solid weighed.

Discussion: During the extraction step of the experiment, no sources of error were identified. This step seemed to have been done correctly since the neutralization and filtration of the compound was a success. During the evaporation step when the substance was dried and then evaporated, an error was observed. The diethyl ether did not initially form a solid. This could be due to the temperature being too hot and the compound melting. As a result, this could have affected the results. It is also possible that melting points could be inaccurate. Although this possibility was not determined, it could still be true due to the possibility that the correct temperature was not an accurate recording if the compound was not being watched closely. The melting points recorded correlate to the melting points given in figure 1 so they are believed to be correct, if not, it is important to pay close attention to the compound melting in the future. Conclusion: The percent yield being 89% can have both a positive or negative correlation with the results to this lab. This indicates that almost 90 percent of the reactants in this lab have affected the overall experiment. This also shows that most of the reactants are not being wasted during this procedure. The fact that 11% of the reaction was wasted possibly could negatively affect the overall experiment. Due to the reaction being performed only once, it cannot be determined if this is the true average percent yield often calculated. Since there was error in the experiment, there’s a possibility that it is not an accurate calculation of the percent yield. In the future, the organic compound should be evaporated at a slower rate to ensure there are less errors. References: [1] Casselman, B. Organic Chemistry Lab Manual; University of Alabama at Birmingham: Birmingham, AL 2020; Background and Procedure

[2] Extraction (Part 1). Extraction in Theory and Practice (Part I) (2013). Available at: http://www.chem.ucla.edu/~bacher/Specialtopics/extraction.html. (Accessed: 11th March 2020) [3] Schaller, C. Acid-Base Extraction. Chemistry LibreTexts(2019). Available at: https://chem.libretexts.org/Bookshelves/Ancillary_Materials/Demos,_Techniques,_and_Experim ents/General_Lab_Techniques/Acid-Base_Extraction. (Accessed: 11th March 2020)...