Lab+II+Crystallization+and+Recrystallization

__** Crystallization and Recrystallization **__

__** Introduction **__
Crystallization involves the formation of homogeneous solid crystal structures through intermolecular forces. Generally, in order for these structures to form, a substance needs to be dissolved completely in a solvent and allowed to reform in a controlled environment, with as few impurities present as possible. Depending on its individual chemical properties, a compound will require a specific solvent and a specific temperature range for both dissolving and reforming. As such, the procedure for recrystallization of different compounds may be noticeably different.

Since crystallization is a vital step for obtaining or isolating a pure compound, it is a very common and routine procedure for organic chemists to undertake. It is a process that is used as a tool to yield results from more complicated procedures, such as synthesizing new compounds. In the procedure below, when the molecule recrystallizes slowly, the pieces have enough time to arrange themselves in an orderly fashion and there are no holes, gaps, or pieces that don’t fit. These crystals are in effect pure.

__** Procedure **__
The procedure for this lab can be found in Williamson’s __Macroscale and Microscale Organic Experiments__, 4th edition, Ch. 3 expt. 1, 2, 3, 7.

//**Solutes used in the following lab tests:**//


 * Name //:// Anthracene
 * IUPAC name: Anthracene
 * CAS Number: 120-12-7
 * Molecular Formula //:// C 14 H 10
 * Compound Formula //:// C 14 H 10
 * Name: Benzoic Acid
 * IUPAC name: Benzenecarboxylic acid
 * CAS Number: 65-85-0
 * Molecular Formula: C 6 H 5 COOH
 * Compound Formula: C 7 H 6 O 2
 * Name: Resorcinol
 * IUPAC name: Benzene-1,3-diol
 * CAS Number: 108-46-3
 * Molecular Formula: C 6 H 4 (OH) 2
 * Compound Formula: C 6 H 6 O 2

//**Solvents used in the following lab tests:**//


 * Name: Ethanol
 * IUPAC Name: Ethanol
 * CAS Number: 64-17-5
 * Molecular Formula: CH 3 CH 2 O
 * Compound Formula: C 3 H 6 O
 * Name: Ligroin
 * IUPAC name: Ligroin
 * CAS Number: 8032-32-4
 * Molecular Formula: C 5 H 12, C 6 H 14  , C 7 H 16  ...
 * Compound Formula: Any fully saturated hydrocarbon.
 * Notes: Apparently a mixture of alkanes. No single molecule.
 * Name: Toluene
 * IUPAC name: Methylbenzene
 * CAS Number: 108-88-3
 * Molecular Formula: C 7 H 5 CH 3
 * Compound Formula: C 7 H 8
 * Name: Water
 * IUPAC name: Oxidane
 * CAS Number: 7732-18-5
 * Molecular Formula: H 2 O
 * Compound Formula: H 2 O

Oxidane? What? I don't think there is a chemist on earth that would seriously call water oxidane. Funny.

**__ Data __**
**Part I [Solubility Tests]: **

**Solute and solvent observations: **

**Solvents: ** All three solvents are clear and colorless. The tap water had small particles in the liquid, with high concentrations forming along the walls of the flask. This was the only visibly noticeable difference between the three solvents.

**Solutes: **
 * Anthracene: Very fine white powder. Individual crystals are almost indiscernible. No obvious odor.
 * Benzoic acid: Odorless, white crystalline particles. Long "strings," similar in consistency and appearance to fiberglass. When manipulated, large clumps cling together.
 * Resorcinol: Off-white, luminescent crystals of varying shape and size. Off-colored, yellow particles visible in the mix, but are few in quantity. No discernible odor.

**Solubility tests: **

**Solvent: ** Toluene Room Temperature: Heating:
 * Anthracene: When the anthracene was added to toluene there was immediate separation. There was no dissolution observered
 * Benzoic acid: During the addition of the bezoic acid after mixing there was separation, therefore no dissolution observed.
 * Resorcinol: Upon mixing of the two chemicals there was no noticeable dissolution, it appeared that it was insoluble at room temperature.
 * Anthracene: The solution boiled on contact with the heating mantle. No dissolution was evident.
 * Benzoic acid: Solution, contained in a microscale reaction tube was placed in the heating mantle. Energy was set to 30% of the maximum output voltage. Upon first contact with the sand of the heating mantle, the liquid began to boil. The particles did not dissolve.
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Resorcinol: Following the aforementioned procedure, the solution boiled on contact with the heating mantle. No dissolution was evident.

<span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">**<span style="font-family: 'Arial','sans-serif';">Solvent: ** Water <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Room Temperature: <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Heating:
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Anthracene: Water was introduced and the solid separated into different parts. The majority of the mass of solute floated to the surface of the solution, while a small amount settled on the bottom of the reaction tube. A few particles were suspended in the solution.
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Benzoic acid: Water was introduced and the solid separated into different parts. The majority of the mass of solute floated to the surface of the solution, while a small amount settled on the bottom of the reaction tube. It seemed to be slightly miscible in the water mixture
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Resorcinol: Water was introduced and the solid dissolved almost immediately. Solution color was clear with a yellow tint. More solute was added, but the saturation point was not reached.
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Anthracene: Solute separates into two separate parts. Approximately half of the mass of the solute settles on the bottom of the reaction vessel while the other half floats on the surface. When heated, solute on top of solvent seems to act like a cork. The anthracene on the bottom does not dissolve at 30% of the maximum output voltage
 * <span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Benzoic acid: Crystals are no longer visible on the bottom or in suspension. Solvent may be at the saturation point. Heat was increased to 40% of the maximum output voltage. Within two minutes of the increase in heat, all of the "cork" dissolved into the solution. Some solute remains un-dissolved along the inner walls of the reaction tube, above the liquid line.
 * <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Resorcinol: Upon heating the resorcinol was very miscible in the water. The dissolution was very expeditious.

**Solvent:** Ligroin Room Temperature: Heating: This first experiment almost begs for a table. Try to work for brevity (along with clarity and adequate detail) when you write out your data.
 * Anthracene: Solute condensed on the bottom of reaction tube under the solvent. It was insoluble at room temperature. There was no discernible mixing; the anthracene remained separated.
 * Benzoic Acid: Cold to the touch. off-white cloudy substance in bottom is evident. Appears to have similar properties as a solid when agitatated: mass rolls and moves. Was miscible at room temperature and dissolved readily. Resourcinol: Solute dissolved at room temperature. Minor quantities of orange colored residue evident after dissolution occured along the walls of the reaction tube.
 * Anthracene: ﻿The separation that was present at room temperature still remained even upon heating, there was no noticeable change in the compound while immersed in ligroin.
 * Benzoic Acid: With the introduction of heat, the mixture began a slow boil. When the reaction tube was removed from the heat source, it launched half of it's contents out of the tube. The solute appears to have dissolved in the solution, but there are small particles of something resembling glass collecting along the bottom of the reaction tube.
 * Resourcinol: All of the orange colored substance left after the dissolution at room temperature transitioned from a solid to a liquid. This liquid did not mix with the aqueous solution, it collected along the bottom of the reaction tube, separated like oil and water.


 * Part II [Phthalic Acid]:**

5 drops, approximately 0.5mL of de-ionized water as added to 0.060g of Pthtallic acid. The acid was a fine white powder. With the heating element set at <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%;">30% of the maximum output voltage, the solution was placed in the sand bath. It began to boil, so intermittent heating techniques were applied until the all of the solute was dissolved. <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">Once the solution had dissolved, the reaction vessel was capped with a rubber stopper and taken out of the sand bath to cool. After 15 minutes of cooling, the temperature of the solution had equalized with that of the room. A solid had precipitated in the solution along the bottom of the reaction tube. The precipitate was white and reflected light. The crystals were long and thin, similar to pencil lead, but much finer. <span style="color: black; font-family: 'Arial','sans-serif'; font-size: 10pt; line-height: 115%; margin: 0in 0in 10pt;">The still capped solution was then placed in an ice bath for an additional five minutes. The solution was uncapped, and the majority of the liquid was removed with a pipette. Two drops of ethanol were added to the remaining solid. The tube containing the precipitate and ethanol was placed in a hot water bath with an aspirator evacuating the gaseous phase of the remaining solution and ethanol. Once this step was complete, the crystals were placed on filter paper to complete the drying process. Once dry, the mass of the precipitate was found to be 0.008g.

This is a pretty low yield for this experiment. Was there any evidence that your product snuck out through the filter paper?


 * Part III [Sugar de-colorization]:**

Raw sugar weighed out at 15.003g. Enough water was added to the sugar to dissolve all of the crystals, ≈10mL and then the solution was divided equally into 4 reaction tubes and heated in a sand bath. The samples were placed in the sand bath; the heating mantle was set at 45%. 0.259g of charcoal was weighed out for the first half of the procedure and 0.050g was weighed out for the second half of the procedure. The solution was brought to a boil in the sand bath set at 70%. The experiment was carried out by boiling the sugar and water solution. The sugar was completely miscible in water and dissolved rapidly and readily. Since the sugar still contained molasses the color of the water was a pale yellow. The water was divided into equal portions as directed and placed in separate flasks. 0.259g of charcoal was added to the first half, stirred and heated in a sandbath for 2 minutes. There was no visible reaction between the solution and the charcoal. For the second half of the process 0.050g of charcoal was added to the other half of the sugar water but heated and stirred for a brief amount of time only for 20 seconds. Even with the smaller portion there was still no visible reaction between the charcoal and the solution. I'm not too surprised to hear this. Thanks for doing the experiment.

__**Part IV [Purification of Unknown]:**__

The solute used for this experiment was the product obtained from the aldol reaction in the previous week's lab. The unknown product was a yellow/orange in color and with parts appearing largely chunk like while some appeared flaky in appearance. 0.072g of the unknown product was measured out and put into an Erenmeyer (Erlenmeyer) flask, 9 parts ethanol and 1 part water (9mL:1mL - a solvent pair) was then added. There was no room temperature reaction, the solute and the solvent remained separated. The flask was then placed in a sand bath with the mantle setting on 20%. After 30 seconds the solute began to float but no dissolution was observed. The mantle setting was turned up to 30% for the rest of the procedure. When the solvent started to boil, a majority of the solute was still discernible in the liquid solvent. The solution was light orange in color when taken out of the sand bath. The solution was not de-colorized as per professor's instructions. Once the solution was removed from the sand bath, the crystallization procedure __was then followed according to the text. Purity was tested after recrystallization; results from the tests are available in the analysis and discussion section.__

Use the word "reaction" with caution. In the chemistry lab, we generally restrict its use to situations where one substance is converted to another, i.e. a chemical change. In the case of something being adsorbed onto decolorizing charcoal, it's just a substance in the solution being removed.

__﻿Analysis__

__ **<span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 18px;">Part I [Solubility Tests]: ** __

Ah, here is the table I was wanting to see.

__ **<span style="color: black; font-family: Arial,sans-serif; font-size: 10pt; line-height: 18px;">Part II [Phtalic Acid]: ** __

The percent yield for this process was 13.3% as seen in the calculation below:



Part IV [Purification of Unknown]:

The percent yield for this process was 21% as seen in the calculation below:



calculations look good to me, except for sig figs problems in both of them.

**__ Conclusion/discussion﻿ __**

The solubility of a compound is determined by many factors but one rule of thumb can be stated when referring to hydrocarbon solubility: Like dissolves like. In the above solubility tests the three compounds used were anthracene (slightly polar), benzoic acid (non-polar) and resorcinol (polar); these were the solutes. Polar substances will dissolve other polar substances and non-polar substances can dissolve other non-polar substances but tend to not dissolve polar substances. The solutions used for the solubility tests were ligroin; a non-polar compound, water; a polar compound, and toluene; a non-polar compound. . The crystalline compound was submerged in a solvent and upon dissolving and recrystallization, the impurities remain in the solution.

As noted above, some compounds tend to be more miscible in hot water rather than cold water and alternately sometimes in cold water rather than hot water. This actually is NOT true: solubility of solids in liquids increases with increasing temperature, I think universally. Crystals are the purest form of a compound due to the lattice structure that holds said compound together, shape is important as the molecules need to fit together for the forces to be greater. A compound with an impurity will not be held together as well as a compound with little or no impurities, hence the elevated melting point temperature. If the melting point of the starting compound remained the same after the recrystallization process, the original compound was probably pure to begin with. However, there was an evident rise in melting point temperature, it can be induced that the original compound was impure and the purity was greatly increased after the recrystallization process. The width/narrowness of the melting point range can also help you assess purity.

This conclusion is all quite nice, though I am not seeing a place in your report where you address potential sources of error in a specific way.

**__ Post Lab Question __**

**Q:** //Ty Trate has been feverishly working in the Organic lab to recrystallize a substance he synthesized using hte Nobel-award-winning Heck reaction. Ty started out with 1.106 grams of product with a m.p. of 131.6-144.3°C. After recrystallizing from an ethanol/water mix, he is left with 0.884 g of product that melts from 143.7-144.9°C.//
 * //**[1]** Calculate the percent recovery for Ty, reporting your answer with an appropriate number of significant figures. Show your work.//
 * //**[2]** Then tell me whether Ty appears to have succeeded in purifying his product during the recrystallization, and explain to me how you know.//

__**A:**__
 * __ **[1]** __
 * **[2]** Yes, because the melting point increased and the range tightened, implying a purer compound. As stated above, the higher melting point proves the vailidity of a purer compound because crystals are the purest form of a compound, due to the lattice network. Within the lattice network there is no room for impurities. good answer.

__** NOTES **__

The chemical structures, formulas, and vital statistics of each compound was researched using [|Wolfram Alpha computational knowledge engine] and confirmed using the [|CRC Handbook of Chemistry and Physics [90th Edition]]