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Recall that KD = AI in s. [A] in So where Sx is the extraction solvent and So is the original solvent. A student poured x00.0 mL of O.y M aqueous benzoic acid solution into a separatory funnel and extracted with zo.0 mL of CH2Cl2. The molar mass of benzoic acid is 122.12 g/mol. At the end of the experiment, that is, after separation and evaporation of the organic layer, x.xx g of benzoic acid was obtained. What is the distribution coefficient for this experiment?
Show transcribed image text Recall that KD = AI in s. [A] in So where Sx is the extraction solvent and So is the original solvent. A student poured x00.0 mL of O.y M aqueous benzoic acid solution into a separatory funnel and extracted with zo.0 mL of CH2Cl2. The molar mass of benzoic acid is 122.12 g/mol. At the end of the experiment, that is, after separation and evaporation of the organic layer, x.xx g of benzoic acid was obtained. What is the distribution coefficient for this experiment?

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Nestor RutherfordLv2

19 Jun 2019

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I need to know the procedures of the experiment below :

Separation of a Three-Component Mixture by Extraction â

benzoic acid ethyl 4-hydroxybenzoate diphenyl sulfone

A 1.5-gram sample of a 1:1:1 (by weight) mixture of benzoic acid, ethyl 4-hydroxybenzoate and diphenyl sulfone was added to a 125 mL separatory funnel. Isopropyl acetate (20 mL) was added to the separatory funnel and the mixture swirled until all solids had dissolved. The solution was sequentially extracted with saturated aqueous NaHCO3 solution (4 X 5 mL), then with water (1 X 5 mL); with the aqueous extracts from each extraction being added to a 50 mL beaker (beaker 1). [The separatory funnel should be shaken for at least 1 minute during each of the four NaHCO3 extractions. Venting of the funnel should be done every 20-25 seconds during each extraction. When draining off the aqueous layer in these and all subsequent extractions leave a two mm tall layer of aqueous solution in the separatory funnel. This greatly reduces the amount of organic layer that contaminates the aqueous extracts.] Next the organic layer was extracted sequentially with 5% aqueous NaOH solution (3 X 5 mL) then with water (1 X 5 mL). Each aqueous extract was collected in a 50 mL beaker (beaker 2). [The separatory funnel should be shaken for at least 1.0 minute during each NaOH extraction..] The remaining organic layer is extracted with saturated aqueous NaCl solution (5 mL) and the aqueous layer is discarded [Do not leave any water in the funnel after this extraction]. The organic layer is transferred to a 50 mL erlenmeyer flask (flask 3). The separatory funnel is washed with isopropyl acetate (2 X 2 mL) with each washing being added to flask 3. The organic solution in flask 3 is dried (Na2SO4) then decanted into a tared 50 mL Erlenmeyer flask (flask 4). The drying agent is washed with isopropyl acetate (2 X 1 mL) with each rinse being added to flask 4. The solvent in flask 4 is evaporated to give crude diphenyl sulfone as a white solid: .416 g, 83.2%, M. pt.=121-127oC. [Evaporate the solvent using a hot plate sat on a moderate (4) setting. You must be very careful not to overheat the product when all the solvent has boiled away. The only way to actually know when all of the solvent has been removed is to weight the flask at the point of â presumed drynessâ, then reheat for a few seconds and re-weigh the flask. If the weight does not change, the product is solvent free. An alternative, and probably better, procedure is to evaporate the isopropyl acetate until only 3-5 mL of solution remains, cool, add hexane (10 mL), chill in an ice bath then filter. Both procedures work well. If insufficient time remains to isolate this material on day 1, then store the dried isopropyl acetate solution in your drawer until the next lab period. The solvent will have evaporated by then. Optional: tlc (alumina,

70/30 hexane/ethyl acetate) showed a single spot, Rf = .58. The crude product is recrystallized from toluene to give the crude product; M. pt.= 125-127ï° C.]

The aqueous solution in beaker 1 was acidified (acid to litmus paper) by the addition of 6 M HCl solution to give a white precipitate. [Caution! Foaming will occur due to liberation of CO2] After cooling the resulting mixture in an ice bath for 10 minutes, the solid was isolated by vacuum filtration, washed with ice water (3 X 1ml), and air dried to give crude benzoic acid as a white solid: .358 g, 71.6%, M. pt.= 115-120oC. [OPTIONAL: tlc (alumina, 70/30 hexane/ethyl acetate) showed a single spot (Rf = .03). This material was recrystallized from water to give pure benzoic acid; M. pt. = 118- 120ï°C.]

The aqueous solution in beaker 2 was acidified (acid to litmus paper) by the addition of 6 M HCl to give a white precipitate. The resulting aqueous mixture was cooled in an ice bath for 10 minutes. The resulting white solid was isolated by vacuum filtration, washed with ice water (3 X 1 mL), and air dried to give the crude ethyl 4-hydroxybenzoae: .353 g, 70.6%, M.pt.= 113-117oC. [Optional: tlc (alumina, 70/30 hexane/ethyl acetate) showed a single spot (Rf = .42). The crude material was recrystallized from 1/1 toluene/hexane to give the pure ethyl 4-hydroxybenzoate as a white solid; M. pt.= 115- 117ï°C.]

Experiment: Extraction to seperate benzoic acid and naphthalene.

Procedure-

Place 2 g of a 1:1 (by weight) mixture of benzoic acid and naphthalene in a small beaker; record the exact mass of the mixture in your notebook. Add 35 mL of dichloromethane to the beaker and stir until the solid mixture has completely dissolved. Carefully pour the solution into a separatory funnel.

Add 20 mL of 3.0 M NaOH to the separatory funnel, stopper it, and shake the mixture with frequent venting. When the layers have separated, drain the bottom portion into a clean flask. Pour the aqueous layer into another clean flask labeled âaqueous layer.â Pour the organic layer back into the separatory funnel and extract with a second portion of 3.0 M NaOH. Drain the bottom layer into a clean flask labeled âorganic layerâ and pour the aqueous layer into the âaqueous layerâ flask.

Put the organic layer back into the separatory funnel and shake with 20 mL of saturated NaCl solution. Drain the organic layer into a clean, dry flask and add a small amount of anhydrous calcium chloride to dry the solution. Allow this solution to stand for at least ten minutes, with occasional swirling, then remove the drying agent by gravity filtration; place the filtrate in a round-bottom flask and remove the solvent by simple distillation or by using the rotovap. Once the dichloromethane has been removed, scrape the crystals out of the round-bottom flask into a clean, labeled, tared vial, and determine the weight and melting point of the naphthalene crystals.

Acidify the combined aqueous layers with 6.0 M HCl until the solution tests acidic to litmus paper. A white precipitate of benzoic acid should develop as the solution is neutralized. Chill the solution in an ice bath for at least ten minutes to finish precipitating the solids, then collect the benzoic acid by vacuum filtration. Wash the crystals with a small amount of cold water; then scrape the crystals into a clean, labeled, tared vial and allow to dry. Once the crystals are dry, determine their weight and melting point.

Post-Lab Question:

Write a balanced equation (using structures) for the reaction that takes place when the aqueous layer is acidified with HCl. Why does the precipitate form when the solution is neutralized? (HINT: benzoic acid (slightly soluble in water) and sodium benzoate (soluble in water)