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13 May 2018

7. A chemist added 10.0 g of an unknown alkaline earth metal to 100 mL of 6 M sulfuric acid. After a vigorous reaction with evolution of a gas, only a clear, colourless solution remained. Next, she removed water and excess sulfuric acid from the solution by vacuum to leave a white solid. After recrystallization, she obtained 13.7 g of product, which represented a 65% yield. Chemical analysis of the white solid showed that it did not contain hydrogen. The white solid was found to be soluble in water and did not react with oxygen. (a) Identify the unknown metal with a chemical symbol. You must show your work for credit

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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.]

This is the description from my organic chemistry lab.

Lab Observations and Data

We obtained 1.17g of cyclohexene oxide (clear liquid) and 3 mL of water into a 50 mL flask with a stir bar. When added a single drop of sulfuric acid, the clear liquid started to change to a very, very light yellow/brownish color. We obtained an ice bath on the side in case our mixture started to boil. After the solution stirred for about 25 minutes, we added sodium hydroxide. We inserted a pH paper and it turned a dark blue, meaning basic. Added another drop of sulfuric acid to make it a little less basic. Added the mixture to a separation funnel, shook it around and ended with separated layers. We separated the layers, thinking the bottom layer was the organic layer, when it was really the aqueous layer. So we ended up mixing the wrong layers back together. After some error, we isolated our new organic layer and added some drying agent. We then put that mixture with the drying agent, NaOH, into the rotovap. Our final product was a white powder and weighed 1.51 grams. We then set up a vacuum filtration while boiling water. We boiled our dried organic layer into the hexane. Added two drops of ethyl acetate to help the boiling process go faster. After vacuum filtering it, it weighed .394 grams. The melting point is 91 to 93 degrees Celsius. Our IR spectra matches the "trans" conformation. So for our TLC plate we observed blue dots to match the trans conformation.

The question is "calculate your percent yield" Which is actual yield/theoretical yield x 100. I just dont understand how I get those numbers.

Here is the lab manual description as well.

Procedure for the Preparation of 1,2-Cyclohexanediol Place a mixture of 1.18 g (0.012 mole) of cyclohexene oxide and 3 mL water into a 50 mL Erlenmeyer flask, equipped with a magnetic stir bar. To this mixture with vigorous stirring add one drop of 6 M sulfuric acid (33% H2SO4) Caution: After a short incubation time, the reaction mixture will become quite warm. This epoxide ring opening reaction is very exothermic. (Why?) If the reaction mixture begins to boil, place the flask in a bath of ice and water. Allow the reaction mixture to stir for the next 15 minutes and let it cool to room temperature. Afterwards, add a small amount of 10% sodium hydroxide drop-wise to neutralize the stirring solution. (No more than 3 or 4 drops of 10% NaOH should be necessary.) Place a drop of the reaction mixture on pH paper to check the pH. Extract the product from the reaction mixture into ethyl acetate or diethyl ether (2 x 15 mL). Dry the combined extracts over sodium sulfate. Decant the solution and remove the solvent to yield the crude product (~1 g). The product can be purified by recrystallization from a small amount (~ 5 mL) of hot toluene or hexanes. Collection of the purified product by suction filtration yields 1,2-cyclohexanediol. The cis isomer has a melting point of 97-101 Â°C whereas the trans isomer melts at 101-103 Â°C. Determine the product(s) or products the reaction. Include a percent yield calculation in your report along with the results of your TLC analysis

Preparation of acetyl salicyclic acid (Aspirin) post-lab questions

1.)At the end of the reaction, you were asked to add ice-cold water to the reaction mixture. What do you think is the reason for this? Explain with chemical equations.

2.)How would the % yield of aspirin be changed if the final rinse of the solid product on the filter paper was done with warm water instead of ice-cold water?

3.)If you run a thin-layer chromatography for a mixture containing salicylic acid and aspirin using a 1:1 solvent mixture of ethyl acetate and hexane, which compound do you think would have more R_f value. Explain why? Bring in the structural features in your explanation.

summary Procedure of lab we did:

- Place approximately 0.300 g of salicylic acid in a tared empty 5 mL conical reaction vial. Record the actual weight of salicylic acid used. Using automatic pipet, add 0.8 mL of acetic anhydride (acetic anhydride vapors are very irritating-handle it carefully, in the hood). Add 2-3 drops of concentrated sulfuric acid using a dropper.

-Clamp the assembly so that the vial is partially submerged in the hot water. Turn on the magnetic stirrer. Once the water bath starts boiling, start timing the reaction. When the mixture has been allowed to react at 100 oC (the temperature of boiling water) for 15 minutes, you can consider the reaction to be complete. During the heating time, take about 20 mL of deionized water in a flask and chill it in an ice-water bath.

- After the reaction has gone on for 15 minutes, add very cautiously, drop by drop, 1 mL of deionized water to the reaction vial. At this point you should have a solution in your reaction vial. Remove the reaction vial form the hot water bath, add another 1-2 mL of DI water and let it stand at room temperature for few minutes. Then, detach the air condenser carefully and remove spin vane with forceps. Place the vial in a beaker and cool down to RT. During this time, the aspirin may begin crystallizing. If not, scratch the walls of the vial with a glass rod. Then, cool the vial in an ice-water bath.

- When the vial appears full of crystals, add about 3-4 mL of ice-cold DI water. Filter the aspirin using vacuum filtration (use Hirsch funnel). Leave the filtration setup in place for few minutes-this will draw air through the sample and will help dry aspirin.

Recrystallization of Aspirin:

- Transfer the rest of the crude aspirin to a 25 mL Erlenmeyer flask and do recrystallization using ethanol.

Purity of Aspirin:

- Using the melting point apparatus, determine the melting point of your crude aspirin and the recrystallized aspirin.

- To do FeCl3 test, get 4 test tubes. Place 1 mL of ethanol and 2 drops of 1% FeCl3 solution in each test tube. Add few crystals of salicylic acid to one test tube. Add few crystals of your crude aspirin product to the second test tube. In the thirst test tube, place a few crystals of your recrystallized aspirin. The fourth test tube will be your âblankâ. Shake each of the test tubes and record your observations.