experiment 4-Separation by extraction

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Tarrant County College South East *

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2423

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Chemistry

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Feb 20, 2024

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Andrea Sosa Flores 28 September 2023 CHEM-2423-40001 Experiment 4. Separation by Extraction Objectives: This experiment’s objective is to master the technique by performing a series of steps to separate it using extraction techniques. One of the main objectives of this experiment is to separate two solutes, benzoic acid, and p-dichlorobenzene, using an organic solvent to dissolve carboxylic acid and a neutral organic compound. Then separated by extraction. To perform this part of the experiment, carboxylic acid needs to react with sodium hydroxide to neutralize the reaction. Also, a covalent organic compound insoluble in water will be converted into an ionic compound soluble in water. After those steps are performed, the extraction will be ready to be performed by extracting the aqueous layer from the organic layer of the previous mixture and isolating the aqueous layer by filtration. On the other hand, p- dichlorobenzene will be recovered by evaporating the organic solvent. Another step of the process that the objective is to master is vacuum filtration, which produces a faster and drier product than gravity filtration. Another objective of this experiment is to safely and efficiently set up, operate, and dismantle the required equipment for vacuum filtration, the correct management of organic kit material, and the right use of the separatory funnel, ensuring equipment safety and maintenance. Procedure, Observations, Data and Calculations: Materials: Methylene chloride,1:1 mixture of benzoic acid and p - dichlorobenzene, sodium hydroxide, filter flask, organic kit, flat filter paper, Buchner funnel, separatory funnel, Erlenmeyer flask, watch glass, hydrochloric acid, ice, water, beaker, hot plate, oven, scale. 1. Weight 2 grams of the 1:1 mixture of benzoic acid and p - dichlorobenzene 2. Add 30 ml of methylene chloride in a separatory funnel and then add the 2 g of mixture 3. Place a stopper in the funnel, hold properly with one finger on the stopper and invert the funnel multiple times to mix the contents 4. Release the pressure by opening the stopcock and repeat several times 5. When the mixture is completely dissolved, clamp the funnel upright at the joint in the ring

6. Add 10 ml of 5% sodium hydroxide 7. Remove the separatory funnel and shake it briefly 8. Invert the funnel multiple times and open the stopcock cautiously to release pressure 9. Repeat the process several times 10. When the two layers are clearly separated, clamp the funnel upright 11. Identify the layers, top layer will be the aqueous layer while bottom layer will be the organic layer 12. Remove the stopper and separate the layers in two different beakers Aqueous layer continuous procedure 1. Add concentrated hydrochloric acid dropwise with stirring until the solution is for the most part a white solid of benzoic acid 2. Cool the solution in an ice/water bath 3. Isolate the benzoic acid by vacuum filtration 4. Transfer the solid to a 125-ml Erlenmeyer flask and add 25 ml of water 5. Heat to boiling on a hot plate until benzoic acid dissolves 6. Allow it too to cool slowly at room temperature and observe crystals of benzoic acid 7. Place the flask in ice/water bath for about 5 minutes 8. Collect the crystals by vacuum filtration 9. Allow crystals to dry while the vacuum is running 10. Scrape the crystals onto a reweighed watch glass 11. Allow the crystals to dry in the oven for about 10 minutes 12. Let the crystals to cool after removing from the oven Organic layer continuous procedure 1. Transfer the organic layer into a dry preweighted evaporating flask 2. Remove organic solvent by placing it in the rotary evaporator Continuous procedure for both

13. Weight both benzoic acid and the dichlorobenzene 14. Determine their melting points 15. Calculate the percentage of mass recovery of each Observations and Data Object/ Sample Weight in grams 1:1 ratio mixture of benzoic acid and p -dichlorobenzene 2.0056 g Empty evaporating flask 61.8435 g Empty watch glass 56.2983 g Evaporating flask with p -dichlorobenzene 62.9999 g Watch glass with benzoic acid 57.0946 g In this experiment, two layers were observed: the bottom layer had an oilier composition view, while the top had a more aqueous view. While the experiments were being performed, in one of the steps when the hydrochloric acid was added, a cloudy, almost invisible dissolution was observed. Bubbles were observed while boiling and crystallized at one point of the experiment. On the organic part of the experiment, when rotation occurred, there was some vapor observed on the rotary evaporator machine. Melting Point of samples examined Sample First liquid appearance temperature (C) Complete liquified sample temperature (C) benzoic acid 1 22.2 C 1 23.3 C p -dichlorobenzene 52.6 C 53.5 C Calculations Percent mass recovery % benzoic acid = (grams of final benzoic acid/ (grams of initial 1:1 ratio mixture of benzoic acid and p -dichlorobenzene/2)) Initial weight of 1:1 ratio mixture of benzoic acid and p -dichlorobenzene: 2.0056 g Empty watch glass: 56.2983 g Watch glass with benzoic acid: 57.0946 g Benzoic acid final weight: 57.0946 g-56.2983 g

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Benzoic acid final weight: 0.7963 g Percent yield % benzoic acid: 0.7963/ (2.0056/2) *100 % benzoic acid: 79.41% % p -dichlorobenzene = (grams of final p -dichlorobenzene / (grams of initial 1:1 ratio mixture of benzoic acid and p -dichlorobenzene/2)) Initial weight of 1:1 ratio mixture of benzoic acid and p -dichlorobenzene: 2.0056 g Empty evaporating flask: 61.8435 g Evaporating flask with p -dichlorobenzene: 62.9999 g p -dichlorobenzene final weight: 62.9999 g-61.8435 g p -dichlorobenzene final weight: 1.1564 g Percent yield % p -dichlorobenzene: 1.1564/ (2.0056/2) *100 % p -dichlorobenzene: 115.32% Conclusion: This experiment was successfully conducted, and the objectives were effectively accomplished. Both mass recoveries were calculated, and the results obtained are listed in the calculation area, where benzoic acid was recovered at about 79.41% and p-dichlorobenzene was recovered at about 115.32%. Based on the results obtained for mass recovery, there might be some inevitable sources of error that occurred during the procedures followed, such as loss of material, phase separation, incomplete drying, co-extraction, and analytical errors such as the calibration of the scale. Loss of material is one of the main sources of error that can occur while transferring the liquids from one container to another by adhering to the inner surface, spillage dropping some liquids outside of the container, inadequate mixing, or evaporation when the compound may evaporate in small amounts, or not recovering all the sample from the separatory funnel. Also, incomplete phase separation means that after shaking the mix, there might not be enough time for the phase separation to be completed, or by letting some of the layer go to the other container. Incomplete drying could be caused by many reasons, which might include solvent contamination after the extraction, which affects the purity of the sample, some analytical issues, and chemical reactions where the byproducts might be affected by the presence of water or the organic compounds not drying it enough. The technique used where solvent was extracted can lead to a mixture of compounds in the organic phase that might create some

challenges in purifying the compound. Co-extraction is usually used for organic compounds, but evaporation or an additional sample might be a great source of error in this stage. Some of the analytical errors might be in the scale; it might have zero errors when the sample is placed on the scale; it reads at zero, but it counts extra, resulting in shifted values; or by operation techniques, where placing the object off-center might lead to inaccurate measurements. After the experiments are completed, a way to check the solutes purity is through the melting point, in this case using an electrothermal melting point apparatus to get a more accurate reading of melting points. The theoretical melting point was given in the experiment, where the value for benzoic acid is 122 °C and for p -dichlorobenzene is 53 °C. In the experiment, the data obtained for melting points are the following: benzoic acid 123.3 °C and p -dichlorobenzene 53.5 °C demonstrating that overall the samples where very pure specially p- dichlorobenzene , where the range difference was only .5 °C of the expected melting point, while the benzoic acid differed by 1.3 °C, which is not a significant impurity but more inevitable errors must occur on the aqueous layer or stages performed for this procedure of the experiment. In conclusion, the experiment was successfully performed with clean materials and equipment set up and set down, minimizing sources of error and obtaining accurate data.