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223

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Chemistry

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Dec 6, 2023

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Leuna Sarah CHEM 223 Acid Base Extraction Experiment Lab Partner: Benjamin Introduction: The purpose of an acid-base extraction lab experiment is to separate and isolate specific compounds from a mixture based on their acidic or basic properties. This technique is commonly used in organic chemistry to purify and separate organic compounds, especially those that are not soluble in water but are soluble in organic solvents. Acid-base extraction relies on the principle that acidic compounds can be neutralized and made more water-soluble by converting them into their salt forms, while basic compounds can be neutralized and made more water-soluble by their protonation. Two immiscible solvents are chosen, typically a polar, water-soluble solvent (usually water) and a nonpolar organic solvent. The organic compounds should be soluble in the organic solvent but not in water, while the acidic or basic compounds should be water-soluble in their salt forms. If the target compound is basic (i.e., it has a basic functional group like an amine), the mixture is treated with an acid (e.g., HCl). The acid reacts with the basic compound to form a water-soluble salt. If the target compound is acidic (i.e., it has an acidic functional group like a carboxylic acid), the mixture is treated with a base (e.g., sodium hydroxide, NaOH). The base reacts with the acidic compound to form a water-soluble salt. After extraction, the two layers (organic and aqueous) are separated. The target compound is then recovered from the aqueous phase by neutralizing it (if necessary) to regenerate the original compound, which can be isolated through further purification techniques such crystallization and chromatography. We were assigned an unknown mixture with two compounds, which we extracted using this process. Chemical and Equipment: Weighing scale, separating funnel, 125 and 250 ml erlenmeyer flasks, Büchner funnel, filter paper, spatula, 250 ml beaker, glass rod, melting point apparatus, capillary tubes, thermometer, glass pestle, watch glass, TLC plates, ethanol, DCM, sodium bicarbonate. Procedure: We weighed 3.0 g of the mixture and dissolved it in 30 mL of DCM, then transferred in a separatory funnel to react with sodium bicarbonate and allow separation of the two phases, organic and aqueous. After filtering and separating the two phases, we conduct a second trial of the organic phase to separate into a new organic and aqueous layer. We add hydrochloric acid to the organic phase by checking pH levels, to allow aspirin to precipitate, conduct vacuum filtration and finish crystallization by heating in the oven. Sodium bicarbonate is added to aqueous layer until the caffeine solution is flowing freely. We then checked the melting points of the mixture, organic crude and aqueous crude. Finally, we confirmed our separation results by performing a thin-layer chromatography of the mixture, organic crude and aqueous crude. Results: Aspirin and Caffeine Mixture: 4.02 - 1.02 (filter paper) = 3g

Ca±eine Ca±eine Ca±eine solid Original mixture = 3g. So original aspirin mass = caffeine mass = 1.5g Aspirin extracted: 1.65 - 1.02 (filter paper) = 0.63g % yield: 0.65/1.5 x 100 = 43.3% Caffeine Extracted: 1.52 - 1.02 (filter paper) = 0.5g % yield: 0.5/1.5 x 100 = 33.3% Melting point: Trial 1 1:1 mix= 116.2 - 122.6 ℃ Aqueous crude: 137.6 - 138.1 ℃ Organic crude: 243.5 - 249.3 ℃ Trial 2 1:1 mix= 115.2 - 120.6 ℃ Aqueous crude: 136.3 - 138.4 ℃

Organic crude: 235.3 - 237.5 ℃ TLC: A= 1:1 mix B= organic crude Rf: 2.5/ 6.8 = 0.37 C= aqueous crude Rf: 6.1/ 6.8 = 0.89 Discussion: Our mixture contained aspirin and caffeine in a 1:1 mix. This is further confirmed by the TLC, which confirms there were only two compounds present into the mixture, and no impurities. Thus we can assume that the amount of both aspirin and caffeine in the 3g mix is 1.5g each. Based on our knowledge of acid base theory, most organic compounds are more soluble in DCM than water. Aspirin is a polar molecule with dipole-dipole attraction bonds and an -OH (hydroxyl) segment as part of a carboxylic acid group. This makes it easily dissoluble in other polar liquids, such as water (H2O). Caffeine has a structure similar to purine. Although polar, caffeine is relatively hydrophobic due to its weakly hydrating faces. Thus our mixture was able to dissolve, and the addition of sodium bicarbonate allowed us to pull aspirin from the organic solvent. This was because aspirin is acidic in nature, the base caused a neutralization reaction to form a salt. Two trials were needed for accuracy and a purer extraction. After precipitating and crystallizing them, the melting point ranges we found were close to the actual melting points of the compounds, hence confirming their identity and purity. The TLC plate showed a good separation of our compounds, and the Rf values of B and C individually matched that of the two spots of A. The image shows that the components of B and C have traveled similar distances as those in A. Our yield of aspirin and caffeine however, were low, which could have been due to a myriad of reasons. Loss of material could’ve occurred during transfer of solutions, filtration as well as separation. Consequently, this lab was a combination of melting point technique, chromatography and extraction, and conducted using our understanding of acid-base theory. Despite not having a higher yield of aspirin and caffeine, 43.3% and 33.3% respectively, the melting point and TLC confirmed their purity.

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Assigned questions: 1. Suppose solute A has a distribution coefficient of 1.0 between water and diethyl ether. Demonstrate that if 100 mL of a solution of 5.0 g of A in water were extracted with two 25-mL portions of ether, a smaller amount of A would remain in the water than if the solution were extracted with one 50-mL portion of ether. K= 1= ((5g - x) x 100 ml) / 25x ml 125x = 500 x = 4 g K= 1= ((4g - x) x 100 ml) / 25x ml 125x = 400 x = 3.2 g K= 1= ((5g - x) x 100 ml) / 50x ml 150x = 500 x = 3.3 g 2. Explain the results of the following TLC errors, a) using too much sample; b) using too little sample; c) using a too polar solvent; d) trying to elute a spot of crystalline material which is only partly soluble in the eluent. a) Using too much sample: If you apply an excessive amount of sample onto the TLC plate, it can lead to overloading, where the spots become too large and concentrated. - Overloaded spots may merge and overlap, making it difficult to distinguish and analyze individual compounds. - The Rf (Retention Factor) values may be unreliable because they depend on the distance traveled by the solvent front relative to the distance traveled by the compounds, and an overloaded spot can lead to inaccuracies. - Accurate compound identification or separation may be compromised. b) Using too little sample: When you apply too little sample, the spots may be very faint or not visible at all. - Inadequate sample loading can result in poor separation and difficulties in detecting compounds on the TLC plate. - Quantitative analysis may be challenging, as the spots may be too faint to measure accurately. - The TLC may not effectively serve its purpose of separating and identifying compounds if there isn't enough sample to visualize. c) Using a too-polar solvent: If you select a solvent that is too polar for the compounds you are trying to separate, it can lead to issues.

- Compounds may move up the TLC plate very quickly, and there may be little or no separation between them. - The Rf values may be close to 1, making it difficult to differentiate between compounds. - Some compounds may run off the top of the plate before others have a chance to separate. d) Trying to elute a spot of crystalline material which is only partly soluble in the eluent: When you attempt to elute a crystalline material that is only partially soluble in the eluent, it can lead to incomplete separation. - The TLC plate may show incomplete separation, with some of the material remaining near the starting point or not traveling far enough. - Accurate Rf values cannot be determined, as the compound doesn't migrate fully to its expected position. - Accurate identification of the compound may be challenging, as it may be mixed with impurities or other compounds due to incomplete separation.