Lab Report 4- Base Extraction & Recrystallization PDF

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Lab Report Grading Rubric Extraction

NAME: Rachel Totos

COURSE-SECTION: MW 12pm

Grading Rubric

Calculation

Experimental Procedure & Reaction Table s

Introduction & Reaction Tables

Performance Element

Excellent

Good

Fair

Poor

5 pts: The introduction begins with a statement of the purpose of the lab undertaken and then presents a though, yet, concise, introduction to the chemical theory behind the lab, including a brief discussion of the mechanisms, analytical techniques, etc, At least one diagram supports the written word.

4 pts: The report begins with a statement of purpose. The introduction may miss some of the relevant chemical theory or diagrams, or have a small amount of theory incorrect, but overall demonstrates proficient knowledge about the background material. Final conclusions and overall findings & adequately presented 3 pts: Minor errors in the format or calculations exist, but all required components are present including diagram, quantities, and stoichiometry. The procedure is original and authentic. Some mistakes are present in calculation of rxn table.

2-3 pts: Report may be missing a statement of purpose. Chemical theory background is minimal, contains substantive errors, or lacks application of the theory to the current lab undertaken. Final conclusions and overall findings may be missing, unclear, or lacking detail.

0-1 pt: The introduction does not connect the principles of the laboratory with the chemical theory. Very small amounts of material are presented, and very little original thought is shown.

2 pts: The experimental procedure contains several errors and/or resembles almost exactly the procedure provided by the text with no thought behind the actual procedure followed. One to two components may be missing. Rxn table is incorrect. 3 -2 pt: Some data spectra, tables, calculations, or equations are missing or grossly incorrect.

1 pt: Two or more required components are missing. The procedure is unclear or mimics the text. The procedure lacks or presents incorrect details such as mols, equiv, conc, etc. Details may be missing.

4 pts: Procedural details are written according to the examples provided with the correct format, including product name and reaction diagram. Math (mols, equivs, etc.) is correct. Procedure is original and authentic, and a diagram of the setup is included. Reaction tables are completed and correct.

5 pts: Calculations/equations are shown and explained.

4 pts: Minor errors exist in titles, table presentation, or the description of acquisition method(s) Calculations are shown but have minor mistakes.

0-1 pts: Data section is incomplete. There are little to no spectra, tables, or calculations.

Earned Points

Conclusion &Data Analysis Post-Lab

6 pts: The conclusion accurately restates the purpose of the lab and concisely indicates whether the purpose and goals were achieved. The data collected is explained and used to verify and prove the concluded outcome. Insightful explanations are offered for unexpected results/procedures.

5 pts: The author accurately restates the purpose of the lab. Data are used to solidly verify and prove conclusions, but with some minor errors in theory and analysis. Explanations for unexpected results are offered.

4 pts: The purpose and conclusions of the lab may or may not be correct, but the author of the report makes gross errors in analyzing the data to arrive at any of these conclusions.

3-1pts: Little to no connections between the data acquired and the conclusions of the lab are presented. Data explained contains little thought and depth. 0 if conclusion is copied from a different source!

Points are assigned (0-10 pts)

Total Score (30 pts) à

Lab Report 4 Base Extraction of Benzoic Acid from Acetanilide; Recrystallization of Products Rachel Totos TA: Xuan Duong 28 June 2021

Base Extraction of Benzoic Acid

Introduction The goal of this experiment is to separate 1:1 mixture of acetanilide: benzoic acid and recrystallize each chemical, and analyze using IR and melting point. Base extraction, purifying a solid by recrystallization and isolating crystals via vacuum filtration are carried out in this experiment. In the end, the percent yield of both acetanilide and benzoic acid are calculated. Extraction, also known as liquid-liquid extraction, is the process of isolation and purification of product in a chemical reaction. For an extracting solvent, the extraction process requires that the extracting solvent be immiscible with the original solvent (e.g., water) and form two separate layers (i.e., aqueous and organic layer). Separation of layers is performed using a separatory funnel. The extracting solvent must be able to selectively remove the desired compound and also be easily separated from the solute. Moreover, the extracting solvent should not react irreversibly with the solute being extracted. For this experiment, sodium hydroxide (NaOH) is used for the extraction of a base. Before distillation, drying agents must be used to remove any water or moisture to prevent the water from co-distilling with the liquid and contaminating the distillate. For this experiment, sodium sulfate (Na2SO4) is used as the drying agent; it is inexpensive, slow acting and low efficiency. Multiple small extractions have taken place throughout this experiment as it is more effective as opposed to one large extraction of the same volume. This phenomenon can be mathematically explained using the fraction of solute (FA) equation shown in the equations section. Recrystallization is a process in which a solid is dissolved with an appropriate solvent at elevated temperatures, leaving behind any impurities, that in turn allow crystals to re-form upon cooling, resulting in a solid substance with a higher state of purity. With recrystallization, the process requires a solvent that is not reactive with the desired products and that the desired

products are slightly soluble or not soluble at room temperature, but completely soluble at higher temperatures. On the other hand, impurities such as undesired components are highly soluble at all temperatures. Recrystallization involves the selection of an appropriate solvent, dissolution of a solid to be purified, decoloration with an activated form of carbon and filtration to remove any impurities, formation of a crystalline solid, isolation of the purified solid and finally, the drying of the crystals. Since melting typically occurs over a range, when recording the melting point, the first number in the range will represent the temperature once the sample begins to melt, and the second number in the range will represent the temperature at which the sample has melted completely. For instance, the theoretical melting range for acetanilide is 111°C-115°C, and 121°C-123°C for benzoic acid. Equations pKeq = pKa (acid left) – pKa (acid right) Keq = 10 -[pKa (acid left) – pKa (acid right)] FA=

(

Vo KV x +V o

)

n

Partition Coefficient: K=

Percent Yield:

A [¿ ¿ o] [ Ax ] ¿ ¿

Actual Yield ∗100 % ( Theoretical Yield )

Procedure Extraction To start the extraction process, 1g of the 1:1 mixture of acetanilide and benzoic acid is added to an Erlenmeyer flask and dissolved using dichloromethane (DCM). Once dissolved, the solution is added to the separatory funnel. Be sure flasks and beakers are labeled to avoid confusion later. To extract the benzoic acid from the DCM, 3M sodium hydroxide (NaOH) is added to the separatory funnel using a graduated cylinder. Next, the separatory funnel is capped and shaken with intermittent venting. Venting in between shakes is important as it releases any gas build up that may cause the cap to blow off or the separatory funnel to blow up. Once the layers have settled, the organic (bottom) layer and the aqueous (top) layer are separated into different flasks. See figure two for an illustration of the difference between the organic and the aqueous layer and the reactions that correspond to each layer. The organic layer is then added back into the separatory funnel and washed with 3M NaOH again. This is to ensure that the carboxylic acid is deprotonated to form sodium benzoate. After the second round of shaking and the solution is settled, the organic layer is distilled into separate flask. To confirm that is there is no acetanilide in the aqueous layer, the hydroxide layer is added into the separatory funnel and extracted with DCM. The separatory funnel is then capped and shaken with intermittent venting. Again, the organic layer is separated from the aqueous layer into a different flask. Then, more DCM is added to the separatory flask and the extraction technique is then repeated. Afterwards, all of the organic layers collected are combined into one flask and all of the aqueous layers collected are combined into one flask. In the end, there should be one flask containing acetanilide and DCM and another flask containing benzoate and water.

Acetanilide Acetanilide in the organic layer is then dried using sodium sulfate (Na2SO4) until no clumps are present in the solution. Next, the solution is then filtered via gravity filtration, using a gravity filter and a clean flask. Vacuum filtration may also be used. See figure three, for an illustration of the gravity filtration apparatus and technique. Once the solution has been filtered, the flask is gently heated in order to evaporate the solvent. Once DCM has been removed, only solid acetanilide remains. To recrystallize, the sample is dissolved in a minimum amount of hot solvent (water). To do this, water is boiled on the side and added to acetanilide using a pipette while swirling the solution to dissolve. However, it is important that there is not an excess amount of solvent used as it will decrease the recovery of the solute. Once the acetanilide has fully dissolved, it is then allowed to cool to room temperature, and put on ice for about five minutes. After about a minute, crystals should begin to form. If no crystallization occurred, there may be too much water in the solution and can be solved by simply boiling off the water and trying again. After five minutes, the crystals are filtered via vacuum filtration. For vacuum filtration of the solid sample, a Büchner flask is clamped to a ring stand and a thick vacuum hose is attached. The Büchner funnel with DCM wetted filter paper inside is place on top of the flask. The vacuum is turned on and the solid sample is filtered through the funnel, while washing the collected sample with a few milliliters of cold water. Once complete, the vacuum is turned off to prevent backflow. Refer to figure one for an illustration of the procedure.

Benzoic Acid To start the extraction of benzoic acid, the benzoate is neutralized with acid. The flask containing the aqueous layer is put on ice and 3M hydrochloric acid (HCl) is added to the flask using a pipette and forms a precipitate. This precipitate is the benzoic acid. In this form, benzoic acid is organic and can no longer dissolve in water. Next, the benzoic acid collected is then filtered via vacuum filtration. Once benzoic acid has been filtered, it is then recrystallized using the same steps stated above for the acetanilide recrystallization, including the vacuum filtration process. Refer to figure one for an illustration of the procedure followed by the corresponding reactions that are taking place. Melting Point Next, the isolated crystals are then weighed in order to calculate the percent yield. Once the mass has been recorded for both benzoic acid and acetanilide, the melting point can then be measured. By comparing the actual melting point with the theoretical melting point, the purity and cleanliness of the sample can be determined. To measure the melting point (see figure four), use a capillary and tap a small amount of crystals into the open end. The capillary is then inserted into the melting point machine (figure five) and the machine is turned on to an appropriate temperature that is not too high, otherwise it will result in an inaccurate measurement. By observing through the lens, record the temperature as the sample begins to melt and once the sample has completely melted, and compare to the actual melting point. IR Spectroscopy

Finally, IR spectrums are taken for both acetanilide and benzoic acid in order to confirm that both substances have been extracted successfully. Given the molecular structure of acetanilide, it is expected to see major peaks for an aromatic ring (1450-1600cm-1), C=O (16501850cm-1), sp3 hybridized CH3 (2800-3000cm-1) and N-H (3350-3500 cm-1). For benzoic acid, peaks are expected to be seen for an aromatic ring (1450-1600cm-1), C=O (1650-1850cm-1), and an -OH bond from a carboxylic acid (3600-2200cm-1).

Figure 1. The image above is a flowchart illustration of the reactions that are taking place throughout the procedure for this experiment. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 75.

Figure 2. The image above illustrates the separation of the organic and aqueous layer in the separatory funnel. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 201.

Figure 3. Gravity filtration apparatus. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 67.

Figure 4. Obtaining sample to measure melting point using capillary. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 39

Figure 5. Thomas-Hoover© melting-point apparatus. This image is from the UIC Organic Chemistry Laboratory Manual, pg. 40.

Results IR spectrum for Acetanilide

Figure 6. The image above is the spectrum taken for acetanilide and major labeled with the corresponding functional groups.

IR spectrum for Benzoic acid

Figure 7. The image above is the spectrum taken for benzoic acid and major labeled with the corresponding functional groups.

IR Spectrum for Acetanilide

IR Spectrum for Benzoic Acid

Functional Groups  C=C (Aromatic)  C=O  CH3 (sp3)  N-H  C=C (Aromatic)  C=O  -OH (Carboxylic acid)

      

Wavenumber (cm-1) 1432.45cm-1-1593.20cm-1 1660.09cm-1 3135.38cm-1 3290.30cm-1 1418.16cm-1-1618cm-1 1675.65cm-1 2825.48cm-1

Table 1. Analysis of IR spectrum of acetanilide (figure 6) and benzoic acid (figure 7) by identification of functional groups and their corresponding wavenumber. Wavenumbers highlighted in green mean that the wavenumbers are in-range with the expectations, and the wavenumbers highlighted in yellow represent wavenumbers that are slightly out-of-range of the expectations.

Compounds

Percent Yield

Benzoic Acid Acetanilide

46% 74%

Observed/ Experimental Melting Point Range (°C) 122.6°C-124.1°C 114.8°C-118.3°C

Table 2. Percent yield and experimental boiling point ranges for benzoic acid and acetanilide.

Product Name Structure

Benzoic acid

Acetanilide

Actual Yield Theoretical Yield % Yield Observed Melting point

0.23 g 0.5 g 46% 122.6°C-124.1°C

0.37 g 0.5 g 74% 114.8°C-118.3°C

Table 3. Comparison of properties from the results of the benzoic acid and acetanilide extraction and recrystallization.

Data Analysis Given the IR spectrum for acetanilide (figure six), all expected peaks were seen; however, the peaks for the methyl group and for the N-H bond were slightly out of range of the textbook wavenumber ranges for those functional groups. It was also expected to have had a more intense peak from the C=O, granted it was in the correct wavenumber range. For the IR spectrum of the benzoic acid (figure seven), all of the expected were seen in the textbook wavenumber ranges given for those particular function groups. Although, the -OH peak from the carboxylic acid in benzoic acid is not as broad as it should be, granted the wavenumber is accurate. This could have been due to the y-axis not being prolonged enough in order to clearly see the broad -OH peak.

The observed melting point range for benzoic acid was 122.6°C-124.1°C, and the theoretical melting point range is 121°C-123°C. Taking into consideration that the thermometer is uncorrected, there may be a 1°C-2°C difference. With that being said, the observed melting point for benzoic acid is in range with its theoretical melting point, and in result, the sample seems to be pure and clean. As for the acetanilide, the observed melting point was 114.8°C118.3°C, and the theoretical melting point is 111°C-115°C. With the data provided, the observed melting point is slightly out of range compared to the theoretical melting point. The very slight difference could have been an observation issue—for instance, the sample may have started to melt prior to first point of recording the data. Also, the temperature may have turned up too high, in which can give an inaccurate reading. Another observation for the difference may be the sample is not as pure and clean as it should be. Referencing table three, the theoretical yield for both acetanilide and benzoic acid is 0.5g, given that 1g of a 1:1 mixture of acetanilide and benzoic acid was used. Since the percent yield was provided, the actual yield needed to be calculated using the percent yield equation stated previously in the equations section. By multiplying the percent yield by the theoretical yield, an actual yield for acetanilide calculated to be 0.37g and 0.23g for benzoic acid. The actual yield obtained for benzoic acid was less ideal compared to the actual yield obtained by acetanilide. With those results, it can be figured that the extraction and purification of acetanilide was more successful than the extraction and purification of benzoic acid.

Conclusion

The purpose of this experiment is to separate a 1:1 mixture of acetanilide: benzoic acid, recrystallize each chemical, and analyze using IR and melting point. By analyzing all the data that was collected, it appears as if the extraction and purification of acetanilide was more successful than the extraction and purification of the benzoic acid. This can easily be seen by the percent yield obtained from both compounds—the percent yield for acetanilide was 74% and 46% for benzoic acid. The benzoic acid did not yield even half of the theoretical yield it was supposed to have. Post-Lab Questions 1. (2 pts) 4.2 grams of a compound containing mithril is dissolved in 60 mL of water. The partition coefficient for the compound between dichloromethane and water is 7.1. a) How much of this compound will be in the dichloromethane if you extract it from the water one time with 60 mL of dichloromethane? n Vo Given: F A = KV x +V o K(DCM+H2O) = 7.1 Vo = 60 mL Vx =60 mL n=1 1 60 Solve: F A = (7.1∗60 )+ 60 F A =¿ 0.123

(

)

(

)

b) How much of this compound will be in the dichloromethane if you extract it from the water with four successive extractions using 15 mL of dichloromethane each time, and then combine the dichloromethane extracts? n Vo Given: F A = KV x +V o K(DCM+H2O) =7.1 Vo = 60mL Vx = 15mL n=4 4 60 Solve: F A = (7.1∗15 )+60 F A =¿ 0.017

(

(

)

)

2. (1 pt) Imagine you want to crystallize 3.2 grams of the compound from the above question using boiling water. The solubility of this compound is 25 g per 100 mL in boiling water and 3.8 g per 100 mL in water at 2 ºC. a) What volume of boiling water is needed to dissolve the 3.2 g of this compound? Given: Solubility= 25g/100mL (boiling water) Mass = 3.2g Solve: (100mL/25g) x 3.2g = 12.8mL boiling water required b) How much of this compound will cr...