Extractiion+and+Separation+of+a+Mixture

Merissa Honey, Kerry Gillette, Heather Browning



__ **Introduction:** __
In organic chemistry, extraction of acids and bases and liquid-liquid extraction is a commonly used method. The extracts of vanilla, alcohol, cinnamon, and almond are retrieved through liquid-liquid extraction in order to purify their components so that they can be used for food flavoring. Extraction happens after a chemical reaction has taken place and the organic product is separated from the inorganic substances. (Williamson 126)

A mixture can be made of two or more substances mixed together. Since the substances are physically mixed with each other and are only changed to and from their ionized structures, separation of the components is possible. Depending on the properties of the components that make up the mixture, there are various ways in which separation can occur. The components of the mixture are either soluble or insoluble when placed in the solvent. An organic substance that is not ionized can be converted from a substance soluble in organic solvents into a substance that is ionized which can dissolve in polar solvents, the focal point of this lab. Acknowledging the principle of "like dissolve like," the compounds of the mixture can be transferred to another liquid by changing the ionization state of that molecule which is done by manipulating the pH. This is a pretty nice intro.

__ **Procedure:** __
From experiment described on pg 139 of Williamson 2004.

Drop Test referred to in the following steps: The two liquids in the test tube at any given time are immiscible; the aqueous layer will be determined by adding a drop of deionized water to the test tube. If the water disappears instantly, the top layer is aqueous; if it travels through the top layer before disappearing, the bottom layer is aqueous.
 * 1) Backwash referred to in the following steps: add documented amount of substance to the test tube, mix, allow to separate, then remove substance added.
 * 2) Dissolve 0.18g of the unknown solution into 2mL of MTBE in tube 1.
 * 3) Add 1mL of aqueous Sodium Bicarbonate solution. (Use marked pipettes)
 * 4) Mix tube 1 for three minutes with pasteur pipette (by pulling in liquid and forcefully expelling it from pipette), then allow the mixture to separate.
 * 5) Draw out lower layer from tube 1 and label layers.(See image of test tube)
 * 6) Put lower layer into tube 2, set aside.
 * 7) Add 0.15 mL Sodium Bicarbonate to tube 1, mix, separate and draw out lower layer. Add lower layer to tube 2.
 * 8) Put .2mL of Ether into test tube 2. (Backwash)
 * 9) Add 1mL of 3M aqueous NaOH to tube 1, shake, allow to separate. (Perform drop test)
 * 10) Draw off lower layer from tube 1 and pour into tube 3.
 * 11) Add .15mL Water to tube 1, extract water, add extracted water to tube 3, perform this twice.
 * 12) Backwash tube 3 with 0.15mL of Ether, tube 3 is finished.
 * 13) Add .5mL NaCl to tube 1, mix, remove aqueous layer. Put aqueous layer in a small flask.
 * 14) Add anhydrous calcium chloride pellets to test tube 1, add the pellets until they no longer clump together. Allow to sit for 5-10 minutes.
 * 15) Remove Ether from tube 1 and place in tube E. Repeat once more.
 * 16) Add needed HCl to 2 by drop methods, checking pH on litmus paper the entire time. Enough HCl is added when the litmus paper turns red.
 * 17) Repeat previous two steps to tube 3.
 * 18) Add glass bead to tube 2.
 * 19) Heat tube 2, with hot water bath, to bring carboxylic acid to solution, then cool to room temp. Put over ice bath; remove solvent and dry crystals of --COOH.
 * 20) Repeat step 19 with test tube 3.
 * 21) Pour test tube 3 into evaporating dish and then allow to dry under open hood.
 * 22) Collect melting points from the dry crystals.

Williamson, Kennith L. __Macroscale and Microscale Organic Experiments.__ Houghton Mifflin. Boston MA. 2004. http://www.youtube.com/watch?v=vcwfhDhLiQU
 * Resources:**

__**Data:**__
Started with: 0.183g solid mixture
 * Tube || Resulting mass || Percent Recovery || Appearance || Melting Point || Possible Substance ||
 * 1 || none || 0 || ether evaporated || N/A || Neutral ether ||
 * 2 || 0.018g || 0.018g / 0.183g Initial Mixture * 100%= 9.8% || white crystals || 118-119C || Benzoic Acid ||
 * 3 || Unable to test || Unable to determine || white crystals || Unable to test || 4-tert-butyl-phenol ||

Did you run out of time on Tube 3? I see you've got crystals but no % recovery or m.p..

__**Observations:**__
Steps 1-8: The initial substances (tube 1) used were 2mL MTBE, which appeared as a clear liquid, and the unknown solid, which appeared as white, spiny crystals. The solid was dissolved in the MTBE, and after the addition of 0.15mL NaHCO3, the solution separated into two layers of clear liquid. Steps 7-12: These steps appeared similarly to the previous steps; after NaOH was added to tube 1 and the solution stirred, two layers of liquid separated again. At this point, the bottom layer began to form white crystals within its layer of solution. Upon adding additional 8 drops of water, the crystals dissolved and two clear layers of solution remained. Steps 13-15: Adding NaCL to tube 1 caused the formation of two layer of clear solution, however, the separation line was very slight and challenging to see (much more challenging to see than the separation between oil and water, for example). The lower layer was transferred to a new tube and anhydrous Calcium Chloride was added to it. The Calcium Chloride was in the form of round, white pellets. At first, the mixture remained clumpy. Upon the addition of more Calcium Chloride, the solution became more "mixed" and appeared less cloudy. Steps 16-17: Upon adding HCl to tube 2, a lot of bubbles of CO2 formed, and the solution gained small, white clumps. Bubbles did not form upon adding HCl to tube 3, however it took on a milky appearance. Steps 18-22: White crystals appeared for both tubes 2 and 3. The ether in tube 1 was evaporated, and left no solid behind. Oh, I remember now: the dreaded "milky substance" that you can't get the crystals out of. Bummer.

__**Analysis:**__
Upon extraction of the "lower layer" or step 6, it was believed that the chemical species involved in the transfer to tube 2, was a carbocylic acid that was ionized from the initial solid by sodium bicarbonate. Carboxcylic acids are soluble in water and would therefore be less dense resulting in the "lower layer" between the two substances. The top layer of tube 1 that remained was the organic layer or the phenol which is not soluble in water, is less dense and was not readily ionized by sodium bicarbonate. This phenol and a neutral substance (tube 1) were later separated by the conversion properties of NaHCO3. The combination of NaHCO3 and phenol resulted in the ionization of phenol making it soluble in water and was therefore removed. This demonstrates that sodium bicarbonate converts carboxylic acids into ionized substances and hydroxide ions convert phenols into ionized substances.

Tube 2 was neutralized with the addition of HCl to create a neutral substance as the solution was previously basic. From this addition it is concluded that crystallization was observed in the organic substance of tube 2 (benzoic acid) due to the ionization process. The crystals did not allow for liquid extraction so the crystals were dissolved allowing for extraction. After heating then cooling the extracted crystals, step 19, and drying the crystals the melting point indicated an organic substance determined to be benzoic acid.

Due to time constraints the melting point and percent recovery of the substance in tube 3 was not determined. The substance that was expected was 4-tert-buty- phenol. Due to the ionization and deionization process we determined a phenol was produced, or returned, in the product. For future reference, it's "carboXylic acid," not "carbocylic acid." You've got it written both ways in your report.

__**Conclusion:**__
Ionization of non-ionized substances occurred by the addition of base to organic solids. By the addition of neutralizing solvents, substances were readily availble to be separated allowing for collection of individual compounds from a mixture.

The process of liquid-liquid extraction takes advantage of the chemical properties of compounds, using knowledge of solubility, in order to separate them from each other. This procedure of separation is widely used in chemistry because it does not rely on the physical properties of substances. The two immiscible liquids usually involved in this type of extraction and separation are an organic solvent and an aqueous solution. In the procedure above, //tert//-butyl methyl ether (MTBE) was used as the organic solvent and aqueous HCO3 – for the first separation followed by aqueous OH- for the second separation. The similarities in chemical properties of HCO3- and the ionized form of Benzoic acid (its conjugate base) include similar intermolecular forces which allowed the Benzoic acid to be separated from the MTBE solvent and placed in the lower aqueous layer which could then be extracted from the mixture. In the same way, the chemical properties of 4-//tert//-butyl phenol and OH- were similar and allowed the assumed phenol to be separated out of the MTBE solvent into the lower aqueous layer.

A point of error may have occurred in step 11, when backwashing tube 2. The contents of the entire tube were initially added to tube 3. The step was repeated and the water was extracted and put into tube 3 correctly. Since the melting point and percent recovery were not able to be determined in is not clear how this error impacted the results but the hypothesis is that it would have exaggerated the percent recovery. As noted above, the possible sources of error likely were the inability to completely dry the crystals, the difficulty in fully extracting only one layer, and a lack of time to finish executing the procedure.

Perfecting both the technique and time management of this procedure will benefit the use of organic chemistry in many laboratory settings. Tell me about what you can determine from the melting point on the tube that DID work. Are you confident you've got the right thing? What does the range of melting temperatures tell you about the purity of the stuff in that tube?

This report earned the following scores for: format (2/2) style (2/2) data (3/3) quality of result (1/1) quality of reported data (1/1) conclusion (1/2) error (1/1) post-lab Q (2 free points) for a total of 13/14.