Symbolism In Everyday Use Essay Example

Symbolism of the Quilt In the story “Everyday Use”, Alice Walker focuses on how important heritage and culture can really be in our world today. In doing this Walker uses symbolism, and two different points of view to help us understand the importance of it all. She uses the symbolism of the quilt to play a very big role in explaining how everyone sees and feels things differently. Anticipating Dee’s arrival mama tries to make sure everything looks very nice in hopes of not disappointing her eldest daughter, Dee knowing she is not a fan of the family.

As soon as she got the chance to leave Dee ran for the quickest way out leaving mama, and her little sister Maggie alone. Now because of this Mama really worries about not being an embarrassment to her child, like any mother would. Also with Dee being the only educated one in the family; it puts a little stain on Mama and Maggie. “She remembers feeling “trapped and ignorant” as Dee reads to her and Maggie “without pity’” (Walker 50). Causing Mama to be on edge when Dee is around, because she always tends to flaunt the fact that she has an education, and mama does not.

In some cases, people tend to look down on their heritage and believe that they have risen above where they came from. Dee is a perfect example of this; she basically believes she is too good for her original heritage. As a result, Dee left home to go off to school and very rarely comes back to visit her mother and sister. “Most critics see Dee’s education and her insistence on reading to Mama and Maggie as further evidence of her separation from and lack of understanding for her family identity and heritage”(Farrell 182).

After being on her own she decided to become a part of a whole new culture starting with the changing of her name. “Not Dee,’ Wangero Leewanika Kemanjo… I couldn’t bear it any longer, being named after the people who oppress me” (Walker 53). In doing this, she became active in the African culture of Black Muslim’s, leaving her mother and sister behind, only coming to visit on occasion when she wants something. Every family has some sort of family heirloom that whether big or small it is special to every person in that family in some way.

This is why heritage is so important because it shows where you come from, and it shows that you play a part in this long line of people you know and love. Walker centers her whole story on this one meaning, using the symbolism of two quilts. “While Walker was not the first to write about quilts, she was one of the first to write about the value of the quilt in the Afro-American experience, and she has certainly been one of the most influential writers in rearticulating the value of the quilt and in contributing to its success in the collective imagination at large”(Baker 160).

Walker uses few but descriptive sentences to emphasis how long these two quilts have been in the Johnson family. “In both of them were scraps of dresses Grandma Dee had worn fifty and more years ago. Bits and pieces of Grandpa Jattell’s Paisley shirts, and one teeny faded blue piece, about the size of a penny matchbox, that was from Great Grandpa Ezra’s uniform, that he wore in the Civil War” (Walker 50). In a lot of ways Dee is making fun of where she truly comes from, she is very selfish when it comes to people’s feelings and emotions. Such a reading condemns the older, more worldly sister, Dee, as “shallow,” “condescending,” and “manipulative,” as overly concerned with style, fashion, and aesthetics, and thus as lacking a “true” understanding of her heritage” (Farrell 180). For example, when she says she wants all of these things from her mother’s house to take home with her. She does not even consider whether or not her younger sister might want a few of her great grandmother’s and grandmother’s things. The only reason she wants these items is for the simple fact that she wants them to show how far she has come in life, and how she has made something of herself. Wangero has realized the dream of the oppressed: she has escaped the ghetto” (Cowart 172). Showing the reasoning behind the fact that she thinks the quilts should be hung up somewhere instead of being put to everyday use. Having heard enough of Dee’s plea mama decided to put an end to the conversation. “I did something I never done before: hugged Maggie to me, then dragged her on into the room, snatched the quilts out of Miss Wangero’s hands and dumped them into Maggie’s lap”(Walker 53).

Therefore, Walker uses all these instances to get the point across that heritage is a part of you no matter how hard you try to deny it. Walker also uses two completely different character points of view, to give pleasant depth in the story. Having a daughter who’s too good for her family, in addition to having one that does not let the world change who she is and really values the little things like quilts made by her ancestor’s clothing. This situation was made very relatable to the average person, allowing it to be easy to follow along ith, and also making the story enjoyable to read. Throughout this whole story, Walker talks about an old family heirloom of quilts and their significant to the Johnson family. She talks about how some appreciate them and how others just consider them another piece of art in a gallery. Making you wonder which person you would be in this situation. Whether it be the one that just hangs the quilts up for everyone to see as a piece of art or the one that puts them to everyday use.

Papr Reduction Techniques For Coherent Optical Ofdm Transmission

Reduction Techniques for Coherent Optical OFDM Transmission Bernhard Goebel, Graduate Student Member, IEEE, Stephan Hellerbrand, Graduate Student Member, IEEE, Norman Haufe, Norbert Hanik, Member, IEEE Institute for Communications Engineering, Technische Universitat Munchen, D-80290 Munich, Germany E-mail: Bernhard. Goebel@tum. de ABSTRACT In coherent optical OFDM systems, the large peak-to-average power ratio (PAPR) gives rise to signal impairments through the nonlinearity of modulator and fiber.

We review the most prominent PAPR reduction techniques that have been proposed for mitigating the impairments with regard to their reduction capability, computational complexity and redundancy. Simulation results are presented for Clipping, Selected Mapping, Active Constellation Extension and Trellis Shaping. Keywords: modulation, OFDM, coherent detection, nonlinear fiber effects, PAPR, coding. 1. INTRODUCTION Orthogonal frequency division multiplexing (OFDM) is considered one of the most promising transmission schemes for future 100 Gigabit Ethernet (100 GbE) networks.

In combination with coherent detection, it offers virtually unlimited electronic compensation of chromatic dispersion and PMD [1] as well as record spectral efficiencies [2]-[3]. One major drawback of OFDM signals is their large peak-to-average power ratio (PAPR) which gives rise to distortions caused by nonlinear devices such as A/D converter, external modulator and transmission fiber [4]. Upon transmission along the fiber, the Kerr effect creates distortions through four-wave mixing (FWM) between OFDM subcarriers; the strength of these FWM products depends on the signal’s PAPR [5].

Various PAPR reduction techniques have been proposed in a wireless communications context [6] and for optical OFDM systems [5], [7]-[10]. In Section 2, we review the most important PAPR reduction methods for coherent optical OFDM systems with respect to their performance, complexity and introduced redundancy. Section 3 presents numerical simulation results, and Section 4 concludes the paper. 2. PAPR REDUCTION TECHNIQUES FOR OPTICAL OFDM SYSTEMS In OFDM, a high-data-rate bit stream is demultiplexed into N lower-rate streams which modulate N equally spaced subcarriers.

The data symbols [X0, X1,…,XN-1], which may be taken e. g. from a QPSK or 16-QAM signal constellation, form a complex OFDM symbol (or data block) of length NT as x(t ) = 1 ?X N n=0 N ? 1 n ? e j 2?? ft , 0 ? t ? NT , (1) where ? f = 1 / NT is the subcarrier spacing [6]. For a sufficiently large N, the real and imaginary part of x(t) follow a Gaussian distribution and the signal power has a central chi-square distribution with two degrees of freedom [6], so that very large power peaks occur with nonzero probability.

When the PAPR is calculated from samples of the continuous signal (1), sampling at a rate of at least four times the Nyquist rate is recommendable to fully capture peaks located in between samples [4], [6]. PAPR reduction methods can be broadly classified into two categories. In one group of methods, the signal is manipulated in a way such that peaks are removed; clipping, active constellation extension (ACE) and precoding are examples for this approach.

In contrast, selected mapping (SLM) and trellis shaping (TS) are schemes which add redundancy to the signal, thereby creating a degree of freedom to reshape the signal or to replace OFDM symbols with a particularly large PAPR. In general, PAPR reduction methods are difficult to compare. For a rough comparison, it is common to use the (complementary) cumulative distribution function (CCDF) of the PAPR depicted in Fig. 1 (right). The aim of PAPR reduction schemes is to shift the CCDF curve as much to the left as possible.

However, the complexity, redundancy and the actual benefit of a method cannot be judged from its CCDF alone. 2. 1 Clipping, Active Constellation Extension and Precoding Clipping all amplitudes that exceed a certain threshold is the simplest PAPR reduction technique. Clipping leads to distortions within as well as out of the signal bandwidth [4]. Filtering the out-of-band clipping noise results in peak re-growth, so that an iterative clipping-and-filtering approach may be necessary [6]. Mach-Zehnder modulators inherently decrease the PAPR through their nonlinear modulation characteristic (“soft clipping”).

Active constellation extension (ACE) reduces the PAPR by moving some of the outer data symbols Xn away from the decision boundaries. This is depicted in Fig. 1 (left) for a QPSK constellation. Each constellation point is allowed to be moved within its respective grey-shaded area. The black dots show the resulting constellation of 978-1-4244-4826-5/09/$25. 00 ©2009 IEEE 1 ICTON 2009 Mo. B2. 4 256 OFDM symbols with 256 subcarriers each. ACE requires no side information at the receiver and the BER is expected to improve initially. However, ACE increases the average signal power; scaling it back to the initial power leads to an SNR decrease.

As seen from Fig. 1 (right), the PAPR reduction capability of ACE decreases for higher constellation orders since only the outermost points can be moved. Determining which data symbols to move in order to reduce the PAPR is a convex optimization problem which is solved by iteratively clipping the amplitude in time domain and re-setting the wrongly moved symbols in frequency domain. Hence, ACE has a complexity of two FFTs per iteration [9]. Figure 1. ACE for QPSK (left) and comparison of CCDFs (right). Results shown are for N=256 subcarriers and QPSK (black) and 16-QAM (green).

The PAPR CCDFs of the original signal, SLM and TS are independent of the modulation format, whereas ACE and precoding degrade with increasing modulation alphabet size. The use of precoding for optical OFDM systems has been proposed in [7], [8]. These schemes reduce the PAPR by decreasing the side lobes of the data symbols’ autocorrelation function, either through multiplication with an appropriate sequence or by a discrete cosine transform (DCT). Both precoding methods have comparable performance, but the DCT is much less complex, especially when the number of subcarriers is large [8].

Precoding is a useful PAPR reduction technique at small constellation sizes. For QPSK modulation, it achieves the lowest PAPR while exhibiting the lowest complexity of all methods (cf. Fig. 1). However, when higher-order modulation such as 16-QAM is used to increase the spectral efficiency, the effect of these schemes is limited. 2. 2 Selected Mapping and Trellis Shaping The idea of selected mapping (SLM) is to generate at the transmitter a set of candidate data blocks, all representing the same data, and to select the block with the lowest PAPR [5].

In practice, this is achieved by predefining a number NSLM random phase sequences of length N. The data symbol vector [X0, X1,…,XN-1] is then element-wise multiplied with each phase vector to obtain the set of candidate data blocks. An IFFT operation is required for each candidate block, so that SLM has a relatively large complexity. To let the receiver know which phase vector was used for encoding, log2(NSLM) bits of side information need to be transmitted along with the payload data. Hence, SLM introduces redundancy and reduces the net rate to Rn = N log2M – log2NSLM bits per OFDM symbol.

The CCDF shown in Fig. 1 was obtained for N = 256, NSLM = 16 and QPSK (i. e. M = 4). In this example, two subcarriers have to be reserved for the side information, so the net rate reduces to 512-4 bits per OFDM symbols. Consequently, to ensure a constant net data rate in bits/s, the symbol rate needs to be increased by 1-254/256 ? 0. 8%. In practice, the transmitted side information requires protection by powerful FEC codes. Therefore, SLM schemes in which no explicit side information is required have been proposed [11].

Trellis shaping (TS) is a coding method that is useful for various signal shaping purposes; its use for PAPR reduction in an optical OFDM context has been proposed in [10]. The required encoder and decoder are depicted in Fig. 2. The input bit sequence for one OFDM symbol is split into vectors s and b. The vector b consists of N(log2M ? 1) bits and the ith group of log2M – 1 bits is used as the least significant bits (LSB) of the M-QAM constellation point in the ith carrier. The remaining N most significant bits (MSB) will be used for shaping.

The MSB of ns consecutive constellation points form one shaping symbol, hence there are N/ns shaping symbols. The input vector s consists of N(ns? 1)/ns bits, which are encoded to vector z by using an (ns? 1)? ns inverse syndrome former matrix (H? 1)T of the convolutional shaping code Cs, i. e. z = s(H? 1)T. Consequently, the vector z consists of N bits, which can be used to select the MSB of the QAM constellation points. The original sequence s can be restored from z by using a syndrome former matrix HT of the code Cs according to s = zHT. The shaping code Cs has a rate R = 1/ns and is defined by the generator matrix G.

The PAPR reduction capability is largely independent of the shaping code that is used. An arbitrary codeword c in Cs can now be added to z, while leaving the restored sequence unchanged, s = ( z ? c ) H T = zH T + 0 , due to cHT = 0. This property implies that no explicit side information is required at the receiver. 2 ICTON 2009 Mo. B2. 4 Figure 2. Encoder (left) and decoder (right) for trellis shaping. The major task that remains to be solved is how to identify the codeword c that results in the lowest PAPR when added to z. One option is to evaluate the resulting PAPR for all possible codewords in Cs.

However, this is a very time-consuming approach. Instead, a Viterbi algorithm based trellis search is used in conjunction with a frequency-domain metric which minimizes the subcarriers’ autocorrelation sidelobes [10]. For large N, the computational complexity of calculating the full metric can become prohibitively large; a sub-optimal metric can be used which minimizes the sidelobes only within a given window [10]. As seen in Section 3. 1, this even leads to lower PAPRs after a certain link distance. The general trellis shaping scheme as depicted in Fig. can be universally applied for multiple purposes by using different metrics. An alternative metric for PAPR reduction was reported in [13]. More importantly, any metric that is directly related to the physical frequency-domain impairments (Kerr-induced FWM subcarrier crosstalk) could be readily applied. Due to the redundancy, which is included in each OFDM symbol, TS reduces the net rate to Rn = N (log2M – 1/ns) bits per OFDM symbol. The reduction of the net rate becomes smaller for increasing constellation size and increasing size ns of the shaping symbol. The CCDF shown in Fig. was obtained using ns = 8, corresponding to rates of Rn = 480 bits per symbol for QPSK and Rn = 992 bits per symbol for 16-QAM, respectively. 3. SIMULATION RESULTS 3. 1 PAPR evolution along the link As shown in Fig. 3 (left), any PAPR reduction is partly undone along propagation as the chromatic dispersion decorrelates the subcarriers’ phases. However, the PAPR remains well below that of an unshaped signal for the entire link irrespective of the data rate, as long as the cyclic prefix (CP) length exceeds the channel memory. For the 56. 3 Gb/s signal (100G PolMux incl. verhead), this is the case only for approximately the first 800 km in the simulated configuration (20% CP). The average PAPR at the transmitter is only partly meaningful; the DCTprecoded signal starts off with the lowest PAPR, but increases rapidly. In Fig. 3 (right), different window sizes of the TS metric are compared for QPSK modulation and 10. 7 Gb/s data rate. It appears that smaller window sizes (corresponding to “local” minimization of autocorrelation side lobes) yield higher PAPRs at the transmitter, but a steadier (and eventually better) PAPR performance along the link.

Figure 3. Average PAPR over link distance for different data rates and PAPR reduction schemes (left) and different widow sizes of the metric used for Trellis shaping (right). 3. 2 Performance comparison For a fair comparison, the various schemes should be compared using the Q-factor or BER at their respective optimum transmit powers for a link length of interest. In our simulation setup, we used N = 256, identical 80-km spans of SSMF (D = 16 ps/nm/km, S = 0. 057 ps/nm2/km, ? = 0. 2 dB/km, ? = 1. 3 /W/km, no PMD), ideal MZM, no DCF, EDFA NF 6 dB.

The net rate is 10. 7 Gb/s, the overhead of SLM and TS was allowed for by an 3 ICTON 2009 Mo. B2. 4 increased total data rate. Fig. 4 shows the results for link lengths of 400 km (left) and 1600 km (right). The depicted effective Q-factor Qeff for 16-QAM was calculated from the BER, which in turn was estimated analytically from the SNR. It can be seen that TS (ns = 8, window size N/8) and SLM (NSLM = 16) can improve the maximum Q by > 1 dB, whereas clipping the signal (at optimum clipping level) does only improve the signal quality at suboptimal power levels.

Because of the non-Gaussian symbol distribution (cf. Fig. 1), calculating a Q-factor for ACE is not sensible. For 16-QAM, a Qeff,ACE can be obtained from the inner (unmoved) constellation points. In our simulations, ACE brought no improvements according to this Qeff,ACE. However, as Qeff,ACE cannot be directly related to the BER, ACE may still bring some gain. To judge this fairly, direct evaluation of the BER is required. Figure 4. Q-factor over input power for 400 km (left) and 1600 km (right) link length and QPSK (black) and 16-QAM (green) subcarrier modulation. . CONCLUSIONS We have introduced and characterized several PAPR reduction schemes proposed for coherent optical OFDM systems. These schemes differ significantly in terms of computational complexity, redundancy and reduction capability. All schemes yield the best performance at high signal power levels. At optimum levels, SLM and Trellis shaping can improve the signal quality by decreasing the nonlinear penalty. The schemes differ considerably with respect to the PAPR evolution along the link.

Hence, a good PAPR reduction scheme should guarantee low PAPR values for the entire link distance of interest.

REFERENCES [1] S. L. Jansen et al. : 121. 9-Gb/s PDM-OFDM transmission with 2-b/s/Hz spectral efficiency over 1000 km of SSMF, J. Lightwave Technol. , vol. 27, pp. 177-188, Jan. 2008. [2] Y. Ma et al. : 1-Tb/s per channel coherent optical OFDM transmission with subwavelength bandwidth access, in Proc. OFC 2009, San Diego, USA, March 2009, postdeadline paper PDPC1. [3] R. Dischler, F. Buchali: Transmission of 1. 2 Tb/s continuous waveband PDM-OFDM-FDM signal with spectral efficiency of 3. bits/s/Hz over 400 km of SSMF, in Proc. OFC 2009, San Diego, USA, March 2009, postdeadline paper PDPC2. [4] J. Armstrong: OFDM for optical communications, J. Lightwave Technol. , vol. 27, pp. 189-204, Feb. 2008. [5] B. Goebel et al. : On the effect of FWM in coherent optical OFDM systems, in Proc. OFC 2008, San Diego, USA, Feb. 2008, paper JWA58. [6] S. H. Han, J. H. Lee: An overview of peak-to-average power ratio reduction techniques for multicarrier transmission, IEEE Wireless Comm. , vol. 12, pp. 56-65, April 2005. [7] O. Bulakci et al. Precoding based peak-to-average power ratio reduction for optical OFDM demonstrated on compatible single-sideband modulation with direct detection, in Proc. OFC 2008, San Diego, USA, Feb. 2008, paper JThA56. [8] O. Bulakci et al. : Reduced complexity precoding based peak-to-average power ratio reduction applied to optical direct-detection OFDM, in Proc. ECOC 2008, Brussels, Belgium, Sep. 2008, paper P. 4. 11. [9] B. Krongold et al. : Fiber nonlinearity mitigation by PAPR reduction in coherent optical OFDM systems via active constellation extension, in Proc. ECOC 2008, Brussels, Belgium, Sep. 2008, paper P. 4. 13. [10] S. Hellerbrand et al. : Trellis shaping for reduction of the peak-to-average power ratio in coherent optical OFDM systems, in Proc. OFC 2009, San Diego, USA, March 2009, paper JThA48. [11] S. Y. Le Goff et al. : A novel selected mapping technique for PAPR reduction in OFDM systems, IEEE Trans. Comm. , vol. 56, pp. 1775-1779, Nov. 2008. [12] T. T. Nguyen, L. Lampe: On trellis shaping for PAR reduction in OFDM systems, IEEE Trans. Comm. , vol. 55, pp. 1678-1682, Sep. 2007. 4

Lab Report 3 Steam Distillation And 4 Crystallization

Objective

In lab 3, we need to use steam distillation to extract pure Eugenol from cloves. In lab 4 part 1, we should aim for the highest quality pure crystallization of acetylsalicylic acid from aspirin. In part 2 of lab 4, our objective is to obtain a comparable pure crystallization of benzil from an impure benzil mixture.

Materials

The objective of lab 3 was to extract Eugenol from 75 g of cloves using various solvents and equipment. Water and Dichloromethane were used as solvents, Calcium Chloride as the drying agent, hydrochloric acid as the acid, and Sodium Hydroxide as the base. The equipment used included a thermometer & holder, separatory funnel, classen adapter, 3-way adapter (distillation adapter), triple neck round bottom flask, west condenser, vacuum adapter, Erlenmeyer flask, 500ml & 50 ml beaker, Bunsen burner, rubber tubing, clamp holder & extensions, and graduated cylinder.

For both parts of lab 4, the hot plate was used as the heating source. The substances were heated in a 100ml Erlenmeyer flask and then filtered using filter paper and a funnel with a neck. Beakers, a vacuum flask for additional filtration, and an electronic scale for weighing the crystals were also used. The solvent used for both parts was 95% Ethanol, which was also dripped on the crystals for purification. In part one, ten tablets of aspirin were used, while in part two, two grams of impure benzil were used.

Procedure

In Lab 3, we embarked on a complex experiment that consisted of several steps. Our first task was to acquire 75 grams of cloves and place them inside our triple neck round bottom flask.

We added 200 ml of water to the flask and sealed two of the three necks with stoppers. We placed a Classen adapter into the remaining center neck. In one of the other necks, we placed a separatory funnel, filled with 50 ml of water. In the last neck, we inserted a 3-way adapter. On top of the 3-way adapter, we inserted a thermometer and its holder to measure vapor temperature. We connected the side of the 3-way adapter to a west condenser, which was then inserted into a vacuum adapter. The vacuum adapter was positioned above an Erlenmeyer flask to collect the distillate.

The setup used clamp extensions and holders to support the triple neck round bottom flask and the vacuum adapter, ensuring stability and preventing vapor leakage. The triple neck flask was placed above a Bunsen burner for heating. The water in the flask was heated to boiling point while taking precautions to prevent foaming. The objective was to distill 60 ml of distillate. Once around 30 ml of distillate was collected, an additional 50 ml of water was added from the separatory funnel to keep the cloves submerged.

After collecting the entire 60 ml of distillate, our next step was to remove the water. To do this, we transferred all of the distillate into an empty separatory funnel. We then added 15 ml of Dichloromethane to the funnel and inverted it, causing two layers to form. We released the pressure and drained the organic material from the bottom layer of the funnel into a separate collection beaker. We repeated this process three times. Additionally, we took a 5 ml sample of the Eugenol, which was not yet pure, from the collection beaker for separate experimentation and for weight comparison.

After drying with Calcium Chloride, the remaining impure Eugenol was weighed and stored for later experimentation. The impure Eugenol was then treated with Sodium hydroxide three times in a separatory funnel, following the principle of inversion and releasing pressure. From the two layers formed, we discarded the lower Dichloromethane layer and kept the top aqueous layer each time.

After deprotonating Eugenol in the aqueous layer, it was acidified using Hydrochloric acid. The pH value of the remaining Eugenol was tested using litmus paper. To extract the Eugenol, 15 ml of Dichloromethane was added three times, with each addition followed by inverting and draining the bottom layer. The Eugenol-Dichloromethane mixture was then boiled on a hot plate in a collection jar to evaporate the Dichloromethane. The pure Eugenol obtained was weighed. In the first part of lab 4, we purified ten aspirin tablets and used 10 ml of 95% Ethanol as our solvent.

In an Erlenmeyer flask, the tablets and Ethanol were combined and heated until gently boiling. To prevent bubbling and ensure complete dissolving, the mixture was swirled. The objective was to obtain a transparent liquid with suspended white solid particles. Once achieved, the contents of the flask were filtered using a narrow-necked funnel into a small beaker and allowed to cool to room temperature. Throughout the filtration process, caution was taken to avoid any floating solids from passing through. During cooling, observation was made for any indications of crystallization.

After the beaker reached room temperature, it was transferred to an ice bath for faster crystal formation. Once we confirmed that the crystals had reached their peak, we filtered them and allowed them to dry on filter paper placed in a funnel atop a vacuum flask. Air was continually removed during this drying process. To ensure even distribution, we used ethanol drips to wash and spread the crystals onto the filter paper using a spatula. Finally, after waiting approximately 10 minutes, we scraped off and weighed the dried crystals.

All utensils were prepared for the second part of lab 4. In this second part, we followed a similar procedure with some variations in the solutes used. We took 2.0 grams of impure benzil and mixed it with 10 ml of Ethanol. The identical procedure from part 1 was repeated in part 2. However, our objective in part 2 was to observe a transparent liquid with suspended black powder, unlike what we saw in part 1. Additionally, in part 2, we kept the crystals obtained for future experimentation at a later date.

Class notes

Steam distillation is an effective technique for separating two compounds that do not mix, such as water and oil or Benzene and water. This situation arises because Benzene is a non-polar organic solvent, while water is a polar inorganic solvent. These compounds cannot be mixed due to their contrasting properties. When a substance undergoes vaporization, its vapor pressure must match the applied pressure, causing the liquid to transform into gas. If two immiscible compounds possess equal vapor pressure, they will also have equivalent boiling points. For example, water and naphthalene demonstrate this phenomenon where water reduces naphthalene’s boiling point. The process of boiling water generates steam.

Steam can be utilized for extracting particles through steam distillation, particularly for immiscible compounds. In our scenario, water acts as the solvent, while the cloves serve as the solutes, potentially containing Eugenol oil, which possesses anesthetic properties. To extract the contents of the cloves, they can be boiled using the Gaffney principle of intense heating. By subjecting a cell to high temperatures, it will undergo lysis, causing the release of its internal contents. Eugenol is primarily composed of a benzene ring, hydroxyl group, and methyl group, forming an organic molecule.

The substance Acetyl Eugenol is found in cloves and is derived from a compound called Eugenol. The boiling point of Eugenol is 255 degrees centigrade. One method to purify a solid through crystallization involves using a solvent that can dissolve the solute when heated to its boiling point (reflux). Ethanol, Acetonitrile, Hexane, and Toluene are commonly used solvents for this purpose.

Using water as a solvent is not recommended because of its inorganic and polar properties. An ideal solute does not dissolve at regular room temperature but only dissolves in a heated solvent. If the solute doesn’t dissolve, add more solvent gradually to the heated mixture. When there are no visible particles of the solute left in the mixture, it means complete dissolution. Sometimes, even after dissolution, certain impurities like charcoal may still be visible and floating in the solvent.

Organic compounds are typically colorless or yellow. It is crucial to filter the solvent promptly after dissolving the solute to remove unnecessary impurities. The mixture can be cooled down to room temperature after filtration to facilitate crystallization. If there is an insufficient amount of crystals formed at room temperature, placing the solvent in an ice bath can aid in this process. Filtration can then be used to separate the crystals from the solvent. Ethanol is a suitable choice for washing and drying the crystals without causing them to dissolve when maintained at room temperature.

Our lab involves the use of two solutes: Aspirin and impure Benzil. Aspirin contains Acetylsalicylic acid as its active ingredient, and a binder as its inactive ingredient. At room temperature, Aspirin does not dissolve in Ethanol. However, if Ethanol is brought to a reflux, Aspirin can be dissolved. Once dissolved, the binder will remain floating and needs to be filtered out. Each tablet of Aspirin has 325 mg of active ingredient. We will use 10 tablets, which should ideally yield 3.25 grams (100% yield). When working with impure Benzil, Ethanol can also be used as the solvent.

When Ethanol is heated until it starts to boil and the vapor is condensed and returned to the reaction vessel, the Benzil will dissolve and only its impurities will be left behind. These impurities consist of charcoal particles, which are identifiable due to the black color of the residue that floats on the surface. The removal of these impurities is a simple process that involves filtering the mixture using a funnel and filter paper.

Observations

During the steam distillation lab, we observed that the water & clove mixture turned dark brown when brought to a reflux. As the distillation process proceeded, we noticed a white milky substance floating in the collected distillate. The milky substance was oil, while the remaining component was water.

Upon addition of Dichloromethane to the mixture, an oil layer formed and separated from the water layer. The organic layer settled at the bottom while the inorganic layer rose to the top. To dry the organic layer, Calcium Chloride was used, which caused white particles resembling small Styrofoam specks to float on its surface. After removing and evaporating the Dichloromethane, Sodium hydroxide treatment resulted in two distinct layers forming.

The mixture consisted of two layers: Dichloromethane on the bottom and an aqueous oily white layer on the top. We added Hydrochloric acid to the remaining aqueous oily layer and used litmus paper to test the pH level, which turned pink. The mixture was then treated with Dichloromethane again, resulting in two layers. We separated the organic layer and evaporated the Dichloromethane, which produced a yellow thin film of Eugenol oil. In the crystallization lab, we observed a milky liquid when the aspirin dissolved in refluxing Ethanol.

After the complete dissolution of aspirin, a floating residue of white binder was observed. Subsequently, the binder was filtered out, resulting in a clear liquid. Crystallization initiated as the liquid approached room temperature. Particularly abundant crystal growth was observed when the mixture was placed in an ice bath. The filtered crystals exhibited a white color. In the case of impure benzil crystallization, dark impurities (charcoal) were observed floating on the solution’s surface. Removal of these impurities led to the identification of a yellow, clear liquid that remained.

The crystals obtained via filtration from the yellow liquid were also yellow in color.

Results

75 grams of cloves resulted in obtaining 0.05 grams of pure Eugenol oil, while 10 tablets of Aspirin, amounting to 3.25 grams of Acetylsalicylic acid, provided a yield of 0.94 grams. Furthermore, from 2.02 grams of impure Benzil, we obtained a yield of 0.03 grams of pure benzil.

Discussion

Using steam distillation, we obtained a yield of 0.05 grams of Eugenol oil from 75 grams of cloves (potential Eugenol oil). This brings up a question: why was our yield so small?

A few factors may decrease our yield capacity. These include a lack of control and the use of impure chemicals. Lack of control can manifest in various ways such as poorly fastened joints or leaky thermometer holders, which allow vapors to escape. Additionally, the absence of a vacuum-sealed system can expose the experiment to temperature fluctuations. Moreover, using impure glassware might contaminate the experiment. Furthermore, inadequate reflux of the water/clove mixture can result in reduced pickup of Eugenol by vapor particles. Lastly, a poorly calibrated weighing apparatus can also contribute to diminishing our yield capacity.

Impure chemicals, such as reagents and solvents, can hinder the pure isolation of Eugenol from cloves. For example, impure Calcium Chloride would hinder the drying process, Dichloromethane would not effectively separate Eugenol from water, Sodium Hydroxide would not deprotonate enough Eugenol, and Hydrochloric acid would not sufficiently acidify Dichloromethane for separation. In the crystallization experiments, we obtained only .4 grams of aspirin from 10 tablets, which is significantly less than the ideal 3.25 grams that could have been isolated in a perfect experiment. Similarly, in the crystallization of Benzil, we isolated only .03 grams from the original 2 grams of impure Benzil. These poor results lead us to question what went wrong. Once again, lack of control and use of impure chemicals appear to be the main factors contributing to our unsatisfactory outcomes.

  • Insufficient desired solute dissolving in the solvent
  • Non-dissolved solute being filtered along with impurities
  • Crystallization during filtration causing the filtering of crystals
  • Rapid temperature drop at room temperature trapping impurities
  • Possible loss of crystal parts during drying in vacuum flask
  • Poor isolation of desired substances due to impure solutes or solvents

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