Crystallization+and+Recrystallization+Lab


 * Solubility Tests Experiments Part 1**

The purpose of this lab was to learn how to perform crystallization and re-crystallization as a method for purifying impure substances. Crystallization is a technique used by chemists to purify solid compounds. Crystallization is based on the principles of solubility: compounds (solutes) tend to be more soluble in hot liquids (solvents) than they are in cold liquids.
 * Introduction:**

If a solution is saturated with solutes, heated up to boiling and then allowed to cool, the solute is no longer soluble in the solvent and forms crystals of pure compound. Impurities are excluded from the growing crystals and the pure solid crystals can be separated from the dissolved impurities by filtration. Impurities can also include colors, the color can be extracted with the addition of substances made with porous charcoal.

Solvents used in this experiment include: water, Ligroin and Toluene. Solutes utilized in this experiment include: Resorcinol, Anthracene and Benzoic Acid. The three solutes where each tested with the three solvents to determine which mixture would work the best for the process of crystallization. Nicely stated intro.

1. Solubility Tests with the following compounds: Resorcinol, Anthracene and Benzoic Acid: 2. Perform the solubility test with the compounds mentioned above in each of the following solvents: water, toluene, and ligroin. Pace each compound in a small test tube and then proceed to test each in the solvents. 3. Note degree of solubility in the solvents-cold hot- and suggest suitable solvents 4. Record the observations 5. Place organic solvents and solutions in the container specified. Dilute the aqueous solutions with water and flush down the drain
 * Procedure:**

//Tolunene:// //Ligroin:// || Dissolved Partially Not Dissolved || Solvent gone-solvent present Partially Evaporated || //Tolunene:// //Ligroin:// || Won't mix-Not dissolved Mixed-not dissolved Not Dissolved || Not really dissolved-liquid boiling out Dissolved Dissolved || //Tolunene:// //Ligroin:// || Not dissolved-crystals mixing Dissolved Not dissolved || Totally Disolved NA Solvent evaporating off, crystals left behind, Not dissolved || good job on the chart.
 * Observations:**
 * **Solute** || **Solvent** || **Solubility at Room Temp.** || **Solubility when Heated** ||
 * Resorcinol || //Water://
 * Anthacene || //Water://
 * Benzoic Acid || //Water://


 * Analysis & Conclusion:**

The first part of this lab involved testing solutes and solvents for the proper solubility. When the Resorcinol was dissolved in the three solvents (water, Ligroin, and Toluene), full solubility was not seen. The three solvents were considered unsuitable for the re-crystallization process of Resorcinol for the following reasons: in water, Resorcinol dissolved immediately at room temperature; this is a poor solvent because the re-crystallization would require cold temperatures. Ligroin may have dissolved the solute in the sand bath; however, it evaporated so quickly that the solute became a grainy crystal on the sides of the dry test tube. In toluene, full solubility was not seen; a solid solute was present at all times (and temperatures). Solubility tests for Anthracene resulted in two suitable solvents, Ligroin and Toluene. In each of these solvents, Anthracene was completely dissolved only after heating the solution to boiling (Ligroin) and almost boiling (Toluene). Dissolving upon heating allows the experimenter to slowly re-crystallize the solute with the most purity as the solution cools. Water was considered an unsuitable solvent because complete solubility was not seen, even upon heating. Lastly, Benzoic Acid as a solute yielded suitable solubility results for water only. This solute did not dissolve at room temperature, but upon heating, turned into solution. Benzoic Acid did not completely dissolve, even upon heating in Ligroin, but the solute did dissolve immediately (at room temperature) in Toluene. Both of these results, as seen above, cause these solvents to be considered unsuitable for crystallization and re-crystallization. In this experiment, the possible sources of error include the inability to observe the point when solutes were completely dissolved (due the sand bath) and a need for more solvent. This is most important for the Ligroin and Resorcinol combination; slow heating and an ability to better observe the change in state of the solute may have given a different outcome, despite the multiple efforts of adding extra solvent and close observation. good.


 * Recrystallization of Pure Phthalic Acid -Experiment Part 2**

This experiment introduces recrystallization and allows for experience working with the process of crystallizing.

1. Recrystallize 60 mg (0.06 g) phalic acid from minimum volume of water, using previous data to calculate required volume. Calculations from page 80 of Williamson 5th Ed.: At 14 degrees Celsius: __100ml solvent X ? ml slovent__ = 11.1 ml solvent needed 0.54g solute 0.06g solute I don't understand the two numbers here at the end. Please give more explanation.
 * Procedure:**

__100ml X ? ml solvent__ = 0.33ml Solvent (It is advised to start with less such as 0.25ml of solvent) 18g 0.06

Oh: these are your calculations, right? No need to calculate the volume for cold solvent. The hot solvent number is what really matters.

2. Add solid to a 10 X 100 mm reaction tube 3. Add water dropwise with a Pasteur pipette 4. A boiling stick/stone may be added for even boiling 5. Gently heat solution to boiling on a hot sand bath in an electric heater. Continue to add water drop wise until entire solid dissolves. 6. Cork the tube, clamp as it cooled and observe crystallization. 7. After tube reaches about 22 degrees Celsius, cool it in ice, stir crystals with a pipette, and expel air from pipette by pushing the tip to the bottom of the tube. Then expel air from the tube using the pipette. 8. Cool the tube in ice, add a few drops of ice-cold ethanol to remove the water from the crystals. 9. Connect tube to a water aspirator and warm it in a beaker of hot water. 10. Once the solvent is completely removed, scrape the crystals onto a piece of filter paper, fold the paper over the crystals and squeeze out the water before allowing the crystals to dry. 11. Weigh the crystals and calculate recovery of product.

In the experiment performed in the lab, four trials took place as a result of adding too much of the solvent, problems with the solvent not boiling because of the size of the test tube it was in, and breaking the test tube. The last trial however went smoothly. After the solution was cooled to room temperature, white crystals began to form. After the aspirating the solution, pipetting out the water and ethanol, and scraping the crystals onto filter paper to dry, it was noticed that the crystals were flaky, creamy white, and sparkling. THANK YOU for describing the crystals!! The end weight of the crystals was 0.07 g. There is a sig figs issue here with your measurements. Do not report masses with less precision than the balance gives you. Because the colored particles are what is wanted, it was suggested not to decolorize. This comment doesn't make sense if your recovered crystals were white, as you report. Start weight of the crystals: 0.06 g End Weight of the product: 0.07 g Percent Recovery: 117%
 * Observations:**

After finding the appropriate solvent, it is possible to complete the process of crystallization and re-crystallization, which is an important step in learning how to purify solids. Observing this process in the second experiment allowed the experimenters to watch and document the solute dissolve in a saturated solution, followed by the growing of the crystals of Phthallic Acid in a reaction tube and to experience treating the solution (to remove all liquid) to render a purified solid crystal as an end result. **Procedure**: **Part Three: Decolorization**
 * Conclusion:**

**Introduction:**

The process of decolorization is an important laboratory technique in that it removes unwanted impurities. In this activity, charcoal is used as a decolorizing agent to further purify raw sugar. The impure elements remaining in raw sugar consist of molasses, a byproduct of the sugar refining process. White sugar has been completely decolorized, while raw sugar and brown sugar retain differing amounts of molasses. The degree of decolorization is due to the amount of times the sugar has been boiled, filtered with charcoal, and recrystallized. In this activity, raw sugar (which has been through several stages of decolorization,) was decolorized again in order to remove additional molasses.

1. 15.1g raw sugar and 30mL deionized water measured out separately. 2. The water was heated over a sand bath 3. The sugar was placed in a 50mL flask 4. 15mL hot solvent (water) was added to the sugar in the flask, and heated over a second sand heater. 5. The solution was brought to a boil, and the second 15mL of hot solvent was added. 6. Once dissolved, half of the solution was poured into a second 50mL flask. 7. 250mg norit charcoal was added to flask A, and 50mg norit charcoal added to flask B. The flasks were allowed to cool. 8. The solutions were observed for color change indicating decolorization.
 * Procedure:**
 * See note at the bottom of Report.**


 * Data:**


 * Amount Charcoal || Before charcoal added || After Charcoal added ||
 * 250mg || golden brown || slightly lighter golden brown ||
 * 50mg || golden brown || no change ||

The raw sugar consists of large, rectangularly shaped crystals that are golden brown in color. Once dissolved in hot solvent (water), the solution gained a golden brown color. Once removed from heat and allowed to rest, a small change in color was observed in the solution to which 250mg of charcoal had been added.
 * Observations:**

Data Analysis: The charcoal did not seem to have a strong decolorizing effect on the raw sugar. This could be due to the fact that the process was only done once, as information from a few articles suggests that multiple decolorizing trials are needed to decolorize sugar noticeably, often involving other decolorizing agents such as hydrogen peroxide, calcium hydroxide and carbon dioxide, and other chemicals along with centrifuging the crystals. The impurities in brown sugar are within the residue of molasses, which contains vitamins and minerals including calcium, magnesium, potassium and iron. Once completely decolorized, sugar no longer contains these additional products. The raw sugar used in this activity had been partially decolorized already, however, charcoal did not significantly decolorize it further.

[] [] [] http://books.google.com/books?id=SDNOAAAAYAAJ&pg=PA1017&lpg=PA1017&dq=organic+chemistry%2Bdecolorization&source=bl&ots=hgjU2RzWqA&sig=0cdilUo5S2JZS7JnccVwXUukJ8g&hl=en&ei=-YjHTLfGHYqgsQPtpbHMDQ&sa=X&oi=book_result&ct=result&resnum=3&ved=0CB4Q6AEwAg#v=onepage&q=organic%20chemistry%2Bdecolorization&f=false http://www.greenlivingtips.com/articles/73/1/White-sugar-vs-raw-sugar.html http://en.wikipedia.org/wiki/Molasses Thank you for looking in to this for me. Nice work.
 * Resources:**


 * Part 7: Recrystallization**

The purpose of crystallization and recrystallization is to separate and purify compounds. It is a technique used frequently in organic chemistry laboratory activities, and chemistry in general. Typically, a solid compound containing undesired impurities is dissolved in the smallest amount of hot solvent possible, cooled allowing crystals of the desired compound to form, and the impurities are filtered out. The success of the activity depends on the assumed difference in solubilities of the desired compound versus the undesired impurities; ideally, the desired compound will become insoluble and crystallize before the impurities as the solution cools. It is possible for the impurities to begin to crystallize as well, but after filtration, their overall amount will be decreased. Repeating the procedure several times will decrease the impurities, hopefully to the point that they are fully removed. If the impurities become insoluble in the solvent before the desired compound (as the solution cools,) a different solvent is needed.
 * Introduction:**

1. measure 180-200mg aldol product (solute) 2. Measure 90%/10% ethanol/water solution (solvent) 3. Heat the solvent in a flask on a sand heater 4. In a separate test tube, transfer an amount of hot solvent that is less that the recommended amount needed to dissolve the solid 5. Heat the solvent-solute mixture to a boil over the hot sand bath, observing for dissolution 6. Add hot solvent slowly as necessary until all solid is dissolved 7. Using a hot filtration technique, filter the solution through a microfilter into a 50mL flask ensuring that it remains hot while flowing through the filter. Rinse the filter with hot solvent to ensure that all solution has washed through the filter leaving only undissolved or undesired impurities in the filter. 8. Allow the flask of filtered solution to cool in an ice bath, observing for the formation of solids. 9. After ten minutes, remove the flask from the ice bath. 10. Filter the solution with crystals through an aspirator. 11. Dry the resulting solid, find the overall mass and melting point.
 * Procedure:**

Unknown: 0.19g aldol product Again, I need all the digits you get off the balance. Your precision here needs to be greater. Solvent: 90%/10% ethanol/water solution Starting volume of solvent: 5mL Ending volume of solvent which dissolved solid almost entirely: 7mL Resulting solid after recrystallization:0.052 g Melting Point: 172.5 degrees Celsius I need a m.p. range, rather than a single temperature. The range is important because (a) all substances experimentally melt over a range of temps, and (b) the size of that range provides important information about purity, as we learned in the melting point lab. Expected Melting Point: 143.7-144.9 degrees Celsius (By comparing this melting point to the one found in lab indicates that impurities were still present in the product) This m.p. range is from the post-lab question. It is not the expected range from our aldol product. Oops.
 * Data:**

The aldol product used appeared to contain yellow and brown particles in chunks and ground powder. The solvent was clear, and began to boil quickly. As the solid began to dissolve in the test tube of the initial 5mL amount of solvent, the solution became a burnt orange/amber color with small, light yellow solid particles on the bottom of the tube. The solution remained dark, even after two more milliliters were added, bringing the total solvent to 7mL. At that point, it became clear that the addition of further solvent would not dissolve these yellow particles, as they had plenty of time to dissolve at boiling temperatures. The hot solution appeared to change in appearance upon being poured into the filter, and as it dripped into the flask. It gained a "fuzzy," "goopy" appearance, that was lighter in color than the previous amber solution. It was difficult to tell whether the product forming was a solid or oil. After cooling to room temperature, the solution was mostly opaque with the "goopy" appearance, but the difference between solid and solution became very visible after the flask was cooled in the ice bath for ten minutes. The low temperature in the ice bath encouraged recrystallization, and a distinct clear, orange liquid with yellow/orange solid was noticeable. The solution had not "oiled out," fortunately. The resulting solid retained by the aspirator filter was a whitish powder, while the solution in the flask was amber in color.
 * Observations:**

It was very clear that the aldol solid had many impurities, making it an ideal candidate for the recrystallization process. It was fascinating to watch the separation of the original brown and yellow parts of the solid into a light crystal product and an amber solution. It appeared that a third compound was present in the small, light yellow powder that did not dissolve at all in the ethanol/water solvent. After observing all the steps and the results of those steps, the desired compound consisted of the light colored crystal material in the aldol product, not the dark brown material. This indeed was the product that was retained in the final aspirator filtration. This indicates that the white and brown solids had different solubilities in the solvent, and as desired, the white solid became insoluble in the solvent sooner as the solution cooled, allowing for it to be separated into a pure crystalline form from the undesired impurities. There are many possible sources of error in this activity, not limited to those suggested in the lab instructions. If any error was made in regards to improper amount of solvent used, it would be "too little" solvent, however, as noted earlier, the addition of solvent did not coax the remaining yellow powder to dissolve and thus appeared to be unnecessary. Unfortunately, the crystals formed were indeed small, but not so small that they were not filtered out of solution. It is likely that wanted solids were lost in the hot filtration step, as the solution began to appear "fuzzy" immediately in the filter, rather than only changing upon arrival in the flask. Keeping the filter hot was a challenging task requiring significant effort, however it is possible that the filter did not remain warm enough. Despite cooling to room temperature before being placed in the ice bath, it is likely that a slower, more exact cooling process would have yielded larger crystals, as it appears now, the crystals appear as a powder.
 * Data Analysis:**

In order to complete a successful crystallization/re-crystallization, it is necessary to have an appropriate solvent. It can be concluded that the best (most suitable) solvent and solute combination will be completely soluble at or near the boiling point of the solution. The three results of solubility observed in this experiment were evaluated for their suitability as a solvent and solute combination based on this idea. Another key technique needed for purifying colored solids was practiced in the third part of this laboratory exercise which is the decolorization through using a porous carbon substance and hot filtration of the solution. A process similar to this is used in the industrial refinement of sugar, turning it into pure white crystals, as well as for decolorizing industrial polymers.
 * Conclusion:**

Altogether, the three experiments performed during the lab period indicated the importance of having an appropriate solvent and solute combination to complete the crystallization/re-crystallization process, knowing how to properly remove liquid solvent from a re-crystallized, pure solid, and having a successful technique of hot filtration. Purifying a solid is valuable to chemists in many different situations, such as the isolation of RNA, identifying compounds in plants, and purifying protein samples.


 * Post Lab Question:**

Ty Trate has been feverishly working in the Organic lab to recrystallize a substance he synthesized using the Nobel-award-winning Heck reaction. Ty started out with 1.106 grams of product with a m.p. of 131.6-144.3 degrees C. After recrystallizing from an ethanol/water mix, he is left with 0.884 g of product that melts from 143.7-144.9 degrees C.

1. Calculate the percent recovery for Ty (he has trouble with math), reporting your answer with an appropriate number of significant figures. Show your work.

0.884 g product/ 1.106 g starting product = 7.99 X 10 -1 = 80.0% sig figs problem here--rounding error. 2. Then tell me whether Ty appears to have succeeded in purifying his product during the recrystallization, and explain to me how you know. He did purify his substance. His melting point range is higher compared to the end product melting point of 143.7-144.9 degrees C. His range of 131.3-144.3 degrees C indicates that his substances are pure because of their higher melting point. This follows the trend in which a pure substance has a higher melting point than a mixture.

Procedures from Experiments 1,2 and 7 from Macroscale and Microscale Organic Experiments 5th Ed., Williamson et. al. 2007. Noted changes in Experiment 2: Use boiling stones, not a boiling stick Noted changes in Disregard directions for heated filtration; rather, use a “water spa”. The “water spa” is a small, empty funnel placed inside a larger funnel containing a hot water bath. It is advised to keep a beaker of hot water (warmed by a hot plate) close on hand to switch out the water in the large funnel as it cools.
 * Resources:**

http://ochemonline.pbworks.com/f/03_recrystallize.pdf http://en.wikipedia.org/wiki/Recrystallization_(chemistry)