Are Eyewitness Identifications Reliable?

Are Eyewitness Identifications Reliable? Eyewitness testimony is one of the most commonly employed forms of direct evidence presented in court and is often more persuasive to juries than circumstantial evidence. Memory is often defined as the processing, storage and retrieval of information acquired through learning. Throughout your day, thousands of sights, sounds, smells and other stimuli from the external environment flood your sensory receptors. All this information, whether paid attention to or not, is briefly held in your sensory memory. Sensory memory is the entry point of memory, where new incoming sense-based information is stored for a very brief period. Short-term memory is a memory system with a limited storage capacity (7 +/- 2 items) and duration. Information is stored temporarily, and assuming that no rehearsal process is used, can be retained fairly well for the first few seconds, but for a longer time than sensory memory. After about 12 seconds, however, recall starts to decline and by 18-30 seconds almost all information disappears if it has not been renewed in some way. The duration can be enhanced if some rehearsal is involved. Long-term memory refers to memory system that stores almost an unlimited amount of information, which can be stored over a lifetime with rehearsal. It comprises of two different systems called declarative memory (specific facts and events) and procedural memory (actions and skills that have been learned previously). Recall and recognition also play a role in the process of retrieving information. Recognition is the ability to elicit stored material (memory) through the use of a cue (Eg. A photo line-up). Recall on the other hand is the ability to elicit stored material without externally providing any type of cue. The reliability of information is an important factor when it comes to identifying suspects and alleged offenders and providing a testimony at trials. Factor One – Age: During circumstances in which a child is a witness to an event, the credibility of that child and whether their testimony is reliable, is often questioned. Young children are able to testify, however they must be found competent before they can do so. The child must be able to understand the obligation of telling the truth, and the effects of lying. If the child is deemed unfit to testify, their prior statements to counsellors, doctors, or law enforcement may be used at trial. Article one: The purpose of first study conducted was to determine whether children as young as 6 or 7 years of age could understand and perform the task of identification, and whether decisional bias and committing fewer false alarms increases with age. Forty eight children were recruited, twenty five male and 23 female. The children were separated into two groups, 2 separate conditions (stealing vs. helping). They were all shown a short video individually, showing four men, dressed in identical red shirts in a soccer locker room. At the end of the video it shows one of the men walking out with two sports bags, one with a New York Yankees logo on it, which had previously been brought in by one of the other men. Each child was given instructions before and after watching the video, which were designed to frame the act, as a moral transgression (stealing) or pro-social (helping). The participants in the stealing condition were asked to identify the man who stole the bag. The others in the helping condition were asked to help the owner of the bags find him to give him a reward. After seeing the film, the participants were asked to say what they had witnessed, what happened in the film, and if they failed to mention that nature of the act (stealing or helping), the experimenter did. The children were then shown a series of photographs, presented sequentially, and for each photo, they were asked to identify whether it was or was not the man. The photos were all taken against an identical neutral background, with them being head-and-shoulders shots with each individual earing the same red t-shirt. In the end the children were asked if they had any questions and were praised for their cooperation, they were then allowed to choose a coloured pen as a reward and given a certificate of appreciation. The data supported the performance hypothesis that, younger children would apply a more negligent criterion when making eyewitness judgements of moral transgressions. The results show th at children in the younger age groups were more prone to make false alarms than children in the 11-14 years age group, and children in the youngest age group were more likely to be very sure that a person was guilty of stealing when he was not, compared to those in the older age groups. In conclusion, younger children are not as reliable when it comes to being an eyewitness to an event. Article two: There is usually a delay from the time a crime is witnessed and a suspect being apprehended, this allows the suspect to undergo a change in appearance, for example changing their hairstyle or hair colour. It is unclear how adults’ and children’s identification abilities compare when the suspect changes their appearance. In a recent meta-analysis, with simultaneous presentation, it showed that children over 5 were as accurate as adults in producing comparable correct identification rates. This study manipulated a suspect’s appearance (hair colour style) to produce ‘no change’ conditions (line-up members match the suspect’s appearance at the time of the crime) versus ‘change’ conditions (line-up members do not match the suspect’s appearance at the time of the crime). Both children and adults were tested. 239 adults were recruited from the introductory psychology participant pool at a university in Eastern Ontario, Canada, an d 96 children recruited from local elementary schools in Eastern Ontario, Canada. Upper body photos were taken resembling the suspect with short, grey hair, or dark mid-length hair. From the assortment of photos, six photos of men that matched the suspect’s description with short, grey hair and six photos that matched the suspect’s description with longer, darker hair were selected to for the line-ups. Two target-present line-ups were conducted, one line-up consisted of six photos, which consisted of five line-up members who had short, grey hair and the suspect’s photo (with short, grey hair). The second line-up consisted of six photos, which consisted of five line-up members who had longer, darker brown hair and the suspect’s photo (with longer, darker, brown hair). There were also target-absent line-ups conducted, one line-up consisted of five foils with short grey hair, with the suspect’s photo replaced with a matching male. The other line-up co nsisted of five foils with darker brown hair with the suspect’s photo replaced with a matching male. The results show that in a meta-analysis comparing the children’s and adults’ correct identification rates, children as young as 5 years of age were found to be able to select the suspect from a group of photos containing the suspect, at a rate comparable to adults. This changed however, when the suspect’s didn’t match his appearance at the time of the crime. For both children and adults’, there was a decrease in their correct identification rates when the suspects appearance changed, they both had great difficulty in correctly identifying the guilt suspect. One reason for a decrease in correct identification following a change in appearance is that eyewitnesses may use hairstyle as a key marker for identification. Overall the elimination procedure is the most effective when it comes to identification rates for both children and adults. Factor two – Stress/Arousal Witnessing a disturbing event (an act of violence) is likely to elicit arousal and to be stressful. Being under stress at the time of encoding can have an effect on the memory process, typically enhancing or preserving memory for emotional information, this can have an interesting implication for eyewitness accounts. Research has found that in the area of emotion and memory has provided evidence that stress influences the long-term memory processes. Article one: The goal of this study was to examine the subsequent effects of misinformation exposure on memory for a negative arousing to-be-remembered event encoded under stress. They adapted a slideshow, with materials from Payne et al. (2006), then added a misinformation manipulation 48 hours after encoding and 48 hour prior to memory testing. Sixty-eight undergraduate students were recruited through the university of Arizona subject pool. Participants were instructed to abstain from alcohol, caffeine, and exercise on days of experimental sessions. Participants were randomly assigned to a two (stress vs. control) and two (misinformation vs. no misinformation). On the first visit, the participants were engaged in a psychosocial stress induction (control task), after they were escorted to another room to few a negatively arousing slideshow. Participants returned forty-eight hours later to the lab to complete the second experimental visit. Upon arrival, the participants were told that they would be asked a series of questions, a totally of 60, relating to the slideshow the view previously two days ago. The questions for the misinformation condition had false information embedded as factual elements of the slideshow (e.g. â€Å"What did the boy have in his hands?† versus â€Å"What did the boy have in his hands besides his lunch?†). The questions were identical in the misinformed and non-misinformed groups to avoid inadvertently cuing one group with information that could potentially benefit the memory performance. The questions asked in this session were designed to expose the participants in the misinformation group to false information. Participants returned another forty-eight hours later after questioning, to complete the third and final experimental session, they were told that their memory of the slideshow would be tested. This was assessed using a recognition test that consisted of 136 questions, administered over a computer. The results showed that bei ng under stress prior to encoding affects memory for a negative event by enhancing subsequent memory. This finding supports the notion that stress influences encoding of aversive events, although stress alone did not moderate misinformation endorsement. Participants were less likely to endorse misinformation for the most negatively-arousing portion of the slideshow if they were stressed prior to encoding, and reported that they were aroused by the negative event. These participants had a more accurate memory for items that had been misinformed with the slideshow phase. The results demonstrate that, in regards to eyewitness memory, arousal induced by an event, in combination with activations of a stressed state, result in an enhanced emotional memory that is less vulnerable to the incorporation of false details, despite being exposed to direct misleading information. Article two: The goal of this study was to investigate how post-encoding stress will affect memory, depending on the thematic arousal of the initial learning period. Predicted that under high thematic arousal, post-learning stress would enhance memory for the central elements of an event, for example a cashbox grabbed by the burglar. Participants were recruited from Bielefeld University, 88 males, ages ranging from 19 to 37. The experiment consisted of four main stages, encoding of an event, manipulation of psychosocial stress, rehearsal of the event information and a recognition test for the event. The first stage consisted of the participants viewing a video-filmed event depicting a burglary. Participants in the high arousal condition should have anticipated to see a distressing, possibily violent incident in the video shown. However those in the low arousal condition were exposed to an event that was unlikely to be as distressing. In second stage, after encoding has occurred, a stress manipula tion was applied. About half of the participants were administered the Trier Social Stress Test, this induced psychosocial stress, the remaining participants were exposed to a non-stressful situation. In the third stage, the participants read a narrative description of the witnessed event, the description did however include items not shown in the original event. In the final stage the participants were given a yes or no recognition test that contained items that did appear in the video and those that didn’t. This study showed that eyewitnesses’ memory for an event was influenced by the combined effect of arousal during encoding and subsequent social stress, which was not related to the event itself. The results indicate that eyewitnesses are likely to experience arousal during observation of an event, they also may be exposed to social stress shortly after, like during an interrogation for example. There was no evidence that thematic arousal and/or post-event stress a ffected the participants’ memory for false post-event information. It is shown that age can have an effect on an eyewitness’s reliability, children are prone to forget things or take into account misleading information and believe it is true. With that being said their credibility is often questioned. Results show that younger children are more prone to making mistakes, and saying someone is guilty, even when they’re not, overall young children are not as reliable. Being under stress at the time of an event can have an effect on memory, however it does not effect on an eyewitnesses memory of an event. These studies show that eyewitnesses are still able to recall the events that happened, even after experiencing pre or post-event stress. At the end of the day, both can have an effect of the recall of information, and identifying the correct perpetrator. Reference List: Echterhoff, G., Wolf, O. (2012). The stressed eyewitness: the interaction of thematic arousal and post-event stress in memory for central and peripheral event information. Front. Integr. Neurosci., 6. doi:10.3389/fnint.2012.00057 Hoscheidt, S., LaBar, K., Ryan, L., Jacobs, W., Nadel, L. (2014). Encoding negative events under stress: High subjective arousal is related to accurate emotional memory despite misinformation exposure. Neurobiology Of Learning And Memory, 112, 237-247. doi:10.1016/j.nlm.2013.09.008 Pozzulo, J., Balfour, J. (2006). Childrens and adults eyewitness identification accuracy when a culprit changes his appearance: Comparing simultaneous and elimination lineup procedures. Legal And Criminological Psychology, 11(1), 25-34. doi:10.1348/13553250552626 Spring, T., Saltzstein, H., Peach, R. (2012). Childrens Eyewitness Identification as Implicit Moral Decision-Making. Appl. Cognit. Psychol., 27(2), 139-149. doi:10.1002/acp.2871

Macbeth/Theme Essy

Takierra Garth Block 50 March 13 2013 (Macbeth/Theme Essy) In the begging where it started off with three creepy witches cackling as they were discussing when they'll meet again, and decide to hook up â€Å"When the hurly-burly's done, when the battle's lost and won. â€Å"(line 3-4) The implication is that they've been up to something really bad. They let the audience in on their plan to meet some guy name Macbeth. And then cut to post-battle, where we learn that this Macbeth has been kicking serious tail in battle so much that King Duncan has decided to give him the title Thane of Cawdor.He's prancing home on a dark and stormy night after defending King Duncan in battle with some skilled enemy-disemboweling. Understandably, he's feeling pretty good about himself. The witches then call out to Graymalkin and Paddock, or spirits that serve the witches. All three witches start to say, â€Å"Fair is foul and foul is fair†(line10-11) before going back about their business. Just then, him and his good friend Banquo run into three bearded witches who rhymingly prophesy that Macbeth will be named Thane of Cawdor and King of Scotland. Just as Banquo is curious about his knowing what he will become.And then they begin to say â€Å"lesser than Macbeth and greater but not so much happy, yet much happier thou shalt get kings. Though thou be none†. (line 65-68) And what they mean by that is he will be fortunate than Macbeth and be father to a long line of future kings of Scotland though he will not be king himself. The next thing we know, a guy named Ross shows up to say that, since the old Thane of Cawdor turned out to be a traitor and is about to have his head chopped off and displayed on a pike, so Macbeth gets to take his place as Thane of Cawdor then that takes care of the first prophecy.His ambitious wife, Lady Macbeth, prods him into acting like a man and killing King Duncan when the poor guy comes to Macbeth's castle for a friendly visit. When Macduf f finds the king's dead body, Macbeth kills the guards and conveniently accuses them of murdering the king. King Duncan's two sons, Donalbain and Malcolm, find out what happened, then they ends up leaving out of Scotland so they can't be murdered too. Macbeth is now named king of Scotland. Now Macbeth starts to worry about the witch's prophecy that Banquo's heirs will be kings.Macbeth's not about to let someone throw him off the throne so, he hires some hit-men name Fleance to take care of Banquo and his son. Banquo is murdered, but Fleance escapes. As Banquo and Fleance live, his mind is full of scorpions. Lady Macbeth states that everybody dies, which may be a warning to Macbeth to cool it, or may be a self-reassurance that everyone has to go sometime, so her husband might as well murder their friend and his kid. At a park near the palace, the two murderers are joined by a third.Only a bit of light remains in the sky. Banquo and Fleance approach on horseback and dismount to walk t he mile to the palace, as usual. Banquo starts up with a friendly conversation and is promptly stabbed. While being stabbed, he encourages Fleance to run away and eventually take revenge. In the meantime, the torch has gone out, and Fleance takes advantage of the darkness to escape. With Banquo dead and Fleance on the run, the murderers head off to the dinner party to report the half of the job they've done.

Samples of Personal Essay for College - What Is It?

Samples of Personal Essay for College - What Is It? How to Get Started with Samples of Personal Essay for College? Occasionally it's helpful to observe how others were able to get over the difficult first-line hump. Regardless of what sort of person you chance to be, you've got to bear in mind that trying to write what you think people wish to hear, or in the manner you think will be expected to lay off your story is a misleading, harmful strategy. Some individuals also lose a feeling of their target audience. Fairly quickly, the remainder of my loved ones followed suitrefusing to wait around for a request for help they realized would never come. What You Need to Know About Samples of Personal Essay for College If a person is writing the work for a college board, for instance, then the tone ought to be somewhat professional and academic, although the language still should show who the writer is. You must grab their attention and the best method to do this is by writing in your voice. Lastly, the detail of real speech makes the scene pop. So that the goal is not just to tell an entertaining tale but in addition demonstrate the reason behind the story and the significance of the experience. Possessing an idea about what you're likely to write about is obviously where you would like to get started. The very first thing you ought to stay in mind is that you will need to write from the heart. There are lots of points to think about. It is almost always better to receive your thoughts in line and work on the very first draft. A Startling Fact about Samples of Personal Essay for College Uncovered Recall unpleasant moments that you discover very handy for your private development. Do not become stuck with material possessions and what you've achieved in life. My roommate nearly known as the emergency room when I got my grades. Realize that's a couple of private mission is my college. The large part of the essay employs standard English and English grammar. While searching for a personal essay example, additionally it is highly recommended that you consider the conditions of use as outlined by different sources. Keep in mind, an admission essay sample may be good way to find out more about the writing procedure and understand the task better. With the aid of ready personal essay examples it's possible to receive a crystal clear picture of the structure, interesting elements and plot twists, which might greatly improve the grade of your essay. Selecting the essay topic for your private essay is easy as you're well acquainted with the subject. If you lack ideas and don't understand where to start, we've prepared a list of private essay topics, which may assist you to begin. So, as soon as you are sitting down to compose an essay, you will need to keep in mind that you need to express your personality there. 1 approach to earn your essay stick out among them is to be sure that your copy is as clean and tight as possible. Indeed, essay topics may vary. Analyze what you have to write in the essay and the way you want the readers to react to it. An essay involve a great deal of thinking and self-analysis. Narrative essays generally have fewer requirements concerning the format when compared to admission essays. Ask three distinct experts what a personal essay is and you will likely get three unique answers. Even though a personal essay could have quite a loose language, you still ought to avoid slang and cliches, which might produce the text much weaker. It is one of the most common types of writing assignment--and not only in freshman composition courses. As any other academic assignment, your private essay needs to be flawless in regards to grammar and punctuation. What is Truly Going on with Samples of Personal Essay for College Keeping your own personal statement concise is particularly important due to the limited character count. Bear in mind, you merely have a couple pages to inform your story, and thus don't devote the first couple of paragraphs rambling about stuff that doesn't matter. You won't ever get bored in the plan of writing because it is similar to ranting all your thoughts in a scholarly and intellectual way. Nothing needs to be repeated in the major body of the essay. Writing your own personal statement is your opportunity to express yourself in your own words. Expressing yourself with written words is a real art.

Breast Cancer Prevention and Education Essay - 1695 Words

According to the American Cancer Society, â€Å"Breast cancer is the common disease of women in the United States, other than skin cancer.† After lung cancer, it is the leading secondary cause of cancer death in women. It helps to have some basic facts about the normal makeup of the breasts to understand breast cancer. In the past, this disease was one of the most feared forms of cancer due to its fatality rate and because complete recovery often required breast removal. The best way to fight this disease is to have a plan that helps you detect the disease in its early stages. Now, however, treatment options have been expanded and there is a higher probability of full recovery than ever before. Lives can be saved by increasing awareness of†¦show more content†¦These ducts lead to the nipple in the center of a dark area of skin called the areola. Fat encloses the lobule and ducts. There are no muscles in the breast, but the rest underneath each and cover the ribs. Thes e common features can from time to time cause the breasts to feel lumpy, especially in women who are poor or who have undersized breasts. Each breast also contains blood vessels and lymph vessels which carry colorless liquid and lead to little bean-shaped organs called lymph nodes. Clusters of lymph nodes found near the breast under the arm, on top of the collarbone, and in the chest. Lymph nodes are also originating in various other parts of the body (Everyday Health, Inc., 2010). According to the National Breast Cancer Foundation, â€Å"Study has shown that women with risk factors are more prone than others to contain the disease because no one knows the exact origin of breast cancer.† Several risk factors can be traced to better ways of identifying and detecting cancer in an early stage and the effect of changes in the way we live by delaying childbirth, taking substitute hormones and oral contraceptives, eating foods high in fat, or drinking excessive alcohol. More risk factors include early menstruation, late menopause and having your first child neither at an aging period nor given birth, and taking birth control for years if women are under age 35. Other risk factors are a family history of breast cancer and concentrated breastShow MoreRelatedCancer Is An Issue Worldwide That Does Not Favor Race,1433 Words   |  6 PagesCancer is an issue worldwide that does not favor race, gender, ethnicity or socioeconomic status. Although, particular cancerâ €™s can effect some individuals more than others. For example, breast cancer. According to the Center of Disease Control Preventions (2017), â€Å"Both women and men can get breast cancer, though it is much more common in women.† In the United States, breast cancer is the second leading cancer among women of any race. 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Breast cancer is the second largestRead MoreThe Issues of Breast Cancer in Nigeria Essay1552 Words   |  7 Pages‘mild breast lumps.’ It is an ailment that could lead to breast cancer. We are happy to see women respond to our awareness programs.† said Dr. Rosa Phil (1). In her article, Dr. Phil commends Mrs. Anyanwu for taking action against breast cancer as she recommends all women do the same. The issue of breast cancer is fast becoming a major one. There is a huge hole to be filled in the area of breast cancer awareness in Nigeria. An article posted in the ‘The Daily Trust’ titled, â€Å"Breast Cancer amongstRead MoreIn Breast Cancer, The Estrogen-Estrogen Receptor Complex1430 Words   |  6 PagesIn breast cancer, the estrogen-estrogen receptor complex cause cell proliferation (Frank, 2013). 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Domestic Violence And Its Effects On Children - 1445 Words

What is domestic Violence? Domestic Violence is described as violent or aggressive behavior within the home, typically involving the violent abuse of a spouse or partner. Many children end up being the victims to seeing domestic violence in the home which is very unhealthy to their development. Some children may development resentment toward both parents- one for not leaving and the other for causing the abuse. Depression, aggressive behavior, emotional distress and suicide depending on the severity are all signs of effects on children. Usually research is examined only for women and the effects that domestic violence has on them, but recently more and more research is being found on how domestic violence has it effects on children. Children in families experiencing domestic violence are more likely than other children to show or display aggressive, antisocial behavior and become depressed and anxious (Brown Bzostek, 2003). Researchers have found higher levels of anger, hostility, disruptive behavior, disobedience, fear and withdrawal (poor peer, sibling, and social relationships) and low self-esteem. Children exposed to domestic violence are at a higher chance of experiencing difficulties in school and score lower on assessments of verbal, motor, and cognitive skills. Slow cognitive development, may not be able to resolve conflicts in a peaceful and calming manner, limited problem solving skills, pro-violence attitudes. (Brown Bzostek, 2003; Edleson, 2006). ResearchShow MoreRelatedThe Effects of Domestic Violence on Children1529 Words   |  7 PagesProject: The Effects of Domestic Violence on Children Trudy Root Kaplan University CM107-11 Children are negatively impacted by the surrounding of domestic violence in multiple ways, in which need to be identified. 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Domestic violence also known as domestic abuse, spousal abuse or child abuse is recognized as a pattern of abusive behavior by one or both partners especially those in marriage. This coercive behavior is used against another person to obtain power and control over the other party in a relationship. Domestic violence takes many forms such as physical violence which includesRead MoreEffects of Domestic Violence on Children1124 Words   |  5 PagesThe biggest victims of domestic violence are the littlest. The home is a suppose to be a safe and secure environment for children with loving parents and free from violence. Children need a secure environment where they can come home to when the outside world is unsafe. However, every year there are millions of children who’s homes are not a safe haven. Millions of children are exposed to a parent being violently assaulted. Domestic violence is a prevalent social issue in America today . 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Determination of traces of heavy metal using anodic stripping voltammetry Free Essays

string(104) " electrode which is subsequent stripping of these metals allows the quantification of these metal ions\." INTRODUCTION Recent studies have shown a rise in the level of heavy metal in the human body and the everyday environment. These finding have increased the importance of heavy metal analysis which have become a major task in areas such as toxicological, epidemiological and environmental research. Trace metal analysis has a wide range of applications these include medical diagnostics, medical device implantation, and pharmaceutical and food analysis etc. We will write a custom essay sample on Determination of traces of heavy metal using anodic stripping voltammetry or any similar topic only for you Order Now In terms of environmental research, pollutants or just the general level of trace heavy metal may be quantified. In a society in which the effects climate change becomes more apparent it is important to be able to monitor and thereby control environmental pollution so as to find way to improve it as well as maintain of ecological balance. There are many well-established analytical methods that are available for detecting, measuring, and monitoring heavy metals. Many of the analytical methods are used for detection in environmental samples .Detection in environmental samples is different to that of laboratory samples in that concentration of element in environmental sample may fluctuate with certain samples having very lower concentrations. Subsequently the need for improvement of analysis technique that are able to detect at lower detection limits is continually sort after so as to obtain more precise results. 1. Trace metal analysis techniques Types of detection method Atomic absorption spectrometry (AAS): This method of analysis determines the elemental composition of a sample via the absorption of light to measure the concentration of gas-phase atoms. It uses lamps whose core is made of the element. The light source is a lamp with a core made of the analyte of interest, this gives off light that is associated with the element and the sample absorbs this light. The analyte atoms in the sample are vaporized in a furnace and transition to higher electronic energy levels when light is absorbed. The concentration of the specific analyte is dependent on the amount of light absorption. Concentration measurements are determined by a working curve after calibrating the instrument with standards of known concentration. AAS is highly specific therefore each element has to be tested separately, this can be a disadvantage when trying to analyse a mixture, as different lamps must be used when measuring different elements. Another disadvantage to this technique is that the samples must be in solution, or at least volatile in order to be measured. There are a large number of factors that may interfere with measurement these include formation of non-volatile compounds and smoke formation which will absorb light, giving this method a relatively low level precision in comparison to other methods. Voltammetry: This studies the behaviour of analytes via the measurement of the potential and current of a sample or cell containing the analyte. There are different categories of voltammetry these include Polarography voltammetry – This process uses DME to produce reproducible effective electrode as a function of time. Linear sweep voltammetry- This process enables pre and post electron transfer reactions to be observed. The potential is linearly increased and the potential range is scanned between the initial potential and final potential Cyclic voltammetry- This is an extension of the linear sweep analysis where by the voltage scan is reversed once maximum current is reach as the as reduction of the analyte would have completed. Anodic stripping voltammetry- determines the specific ionic species by deposition of the analyte and stripping resulting in a redox reaction. The oxidised species registers as a peak Differential pulse voltammetry- Potentiometry: based on measurement of potential of an electrode system consisting of two electrodes, potentiometer and sample containing analyte of interest. This method is advantageous as it can detect ions in presence of whole host of other Substances. The desire for more accurate result had major challenges as developers had to development new analytical methods and improvement of existing methods. In particular, the introduction of powerful modes of atomic absorption spectrometry such as the graphite furnace other newly established analysis techniques include neutron activation Graphite furnace atomic absorption spectrometry (GFAAS): Atoms absorb light at particular frequencies depending on the characteristic of the element. The amount of light absorbed may be linearly correlated to the concentration of the analyte and can thereby be quantified. Samples are deposited into small graphite tube which is subsequently heated to vaporize and atomize the analyte. Neutron Activation: A sample is subjected to a neutron flux and radioactive nuclides are produced. As these radioactive nuclides decay, they emit gamma rays whose energies are characteristic for each nuclide. Comparison of the intensity of these gamma rays with those emitted by a standard permit a quantitative measure of the concentrations of the various nuclides. 1.1 Back ground and history of mercury The dropping mercury electrode was invented in 1922 by Jaroslav Heyrovsky and was the foundation of electroanalytical voltammetry techniques via the development of the first linear sweep voltammetry method of polarography. In the year following between 1947 and 1959 voltammetry at stationary were developed. Electrolysis is the process by which ionic substances are decomposed (broken down) into simpler substances when an electric current is passed through them. In order for electrolysis to occur mass transfer is required between the electrode .Michael Faraday’s Second Law of Electrolysis was established in 1934 and states that â€Å"If the same quantity of electricity (electric charge) is passed through different electrolytes, the mass of a substance librated or deposited altered at an electrode is directly proportional to their chemical equivalents†. This law recognized the quantitative relationshipbetween current and equivalents of elements. The ficks law of diffusion formulae verified this quantitative relationship which enabled In recent years, mercury electrodes were still widely used in the detection of heavy metals by anodic stripping analysis due to its unique features. Heavy metal ions are reversibly reduced to form amalgams with the thin film of mercury on the electrode surface. The mercury film electrode is formed by electrodeposition onto an electrode which is subsequent stripping of these metals allows the quantification of these metal ions. You read "Determination of traces of heavy metal using anodic stripping voltammetry" in category "Essay examples" Mercury is an important electrode in terms of cathodic process study. Due to its low boiling point mercury as an electrode can be used in many forms these include dropping, streaming and pool configuration. 1.2.1 Types of mercury electrodes There are different types of mercury electrode these are as follows – Dropping mercury electrode: This working electrode is usually associated with the voltammetric technique polarography used for environmental analysis, especially for marine study.DME is made from 10-20 cm of glassy capillary tubes with internal diameter of 0.05mm. These dimensions and specification is chose to increase efficiency of the electrode. For example the length of the capillary tubes provides enough static head space to provide a drop time of 3-10 s. There are a number of variations of DME. The vertical orifice capillary has a capillary bent at 90 degrees and removes effect of maxim and depletion where as the Teflon DME is made specifically for use in solution. The reproducibility and vast knowledge about literature make this one of the best electrode for use in electrochemical analysis. Mercury film electrode: a mercury film is formed on an electrode substrate for example glassy carbon, carbon paste and pencil-lead etc. During voltammetric analysis mercury film forms an amalgam with the analyte of interest, which upon oxidation results in a sharp peak, improving resolution between analytes. Hanging mercury drop electrode (HMDE): this is very similar to the DME however HDME produces partial mercury drop of controlled geometry and surface area at the end of a capillary where as DME steadily releases drops of mercury during an experiments. HDME is used for voltammetric techniques requiring stationary electrodes. Mercury-plated electrodes: mercury is electroplated onto a solid electrode. Mercury forms a film or an assembly of micro droplets depending on the substrate on which it is plated. Electrode substrates Types of electrode substrate Glassy carbon electrodes: Produced by placing a thick sheet of glassy carbon into a glassy tube with epoxy cement. The surface of the electrode is then polished until it becomes smooth. Carbon paste electrodes: made by the mixture of graphite and nujol until it develops the consistency of a paste. Carbon cloth electrode: carbon cloth have voltage ranges similar to that of carbon electrode The process of formation is by heating woven hydrocarbon polymer fabric to high temperatures. Platinum electrodes: This involves the use of a fine powder known as platinum black placed on solid platinum. Gold electrode: With the ability to be made into different forms i.e. rods, disc etc it is one of the most commonly used electrodes. Indium tin oxide electrode: transparent electrode generally used for Spectra electrochemical measurement In this case glassy carbon will be used as our electrode substrate, this is because of the many advantage glassy carbon has as an electrode substrate. Glassy carbon has good conductivity, low electrical resistance, thermal expansion coefficient is small, hard texture, good gas tightness, a wide scope of application of electric potential (from about -1 ~ 1V), chemical stability, can be made of cylindrical, disc, etc. These properties make it ideal for use in voltammetric analysis as it allow the flow of current in a controlled way and facilitate the transfer of charge to and from the analyte electrode shape, use it as a matrix can also be made of mercury film glassy carbon electrode and chemically modified electrodes. In the electrochemical experiments or electroanalytical chemistry has been increasing wide range of applications. Advantages and disadvantages of mercury electrodes The mercury film forms Mercury as an electrode is advantageous for many reasons these include its ability to release the contaminated drop and grow a clean drop between each experiment unlike solid electrodes which are required to cleaned and undergo a polishing step in order to prevent contamination of the electrode. This also means the electrode is independent of its past history. Metal ions can be deposited from acidic solutions thought thermodynamic state this is impossible without the formation of hydrogen which causes overvoltage which is associated with the reduction of hydrogen ions. Mercury however has a few limitations, one of which is its ease in oxidation, this causes a limitation in the range of anodic potentials used. When dealing with potential greater than + 0.4 V mercury (I) is formed causing a wave that masks the curve of other oxidized species. This occurs at lower potentials in the presence of precipitating ion or mercury (I) complexes. However the single greate st danger mercury poses as an electrode is its high level of toxicity. Mercury as a compound must be handled carefully, since its toxicity has very serious implications for the health and the environment. Mercury has a major impact on the environment due to its ability to progressively build up in successive trophic levels as well as along the food chain by a process of biomagnification. Over time this build up migrate across both biotic (other organisms) and abiotic (soil, air, and water) sources. At the top levels of the aquatic food web are fish-eating species, such as humans, seabirds, seals etc .In a study performed by the environmental protection agency US of fur-bearing animals in Wisconsin, the species with the highest tissue levels of mercury were otter and mink, which are top mammalian predators in the aquatic food chain. Top avian predators of aquatic food chains include osprey and bald eagle. Thus, mercury is shown transferred and accumulated through several food web levels. Aquatic food webs tend to have more levels than terrestrial webs, where wildlife predators rarely feed on each other, and therefore the aquatic biomagnification typically reaches higher values .In terms of health hazard mercury exposure may result in severe neurological effects, symptoms include convulsions, fits, and highly erratic movements. This was seen in Minamata, Japan, from about 1950-1952 where birds experienced severe difficulties in flying as well as domestic animals, especially cats whose diets were high in seafood exhibiting abnormal behaviour. This exposure was caused by the release of methyl mercury in the industrial wastewater from the Chisso Corporation’s chemical factory, which continued from 1932 to 1968. Chemically modified electrodes The ability of an electrode can be increased by means of chemical modification through the addition of atoms, molecules or nano particles to the surface of the bare electrode increasing its functionality over a wide range. Due to the many disadvantages mercury poses as an electrode, potential replacements for mercury are continually sought. The introduction of bismuth as an alternative has many significant advantages. It has been demonstrated that Bi is a good alternative since it is less toxic and easy to handle. The abilities of bismuth as an electrode are comparable to that of mercury and are attributed Thin Bi film is thus a good substitute candidate for the detection of heavy metals. Bi will be deposited onto the surface of a glassy carbon electrode (GCE) using electrodeposition thereby causing heavy metal ions to form an amalgam with Bi. ASV will be used to determine the concentration of heavy metals. The method by which bismuth is coated on to a electrode plays a huge part in its potential as an electrode. There three main methods by which bismuth may be coated onto an electrode. Ex-situ plating: This process involves the bismuth ions in a solution being moved toward the working electrode which in this case is glassy carbon, by an electric field form by passing a current through the electrode there by forming a bismuth film on the electrode. The coated electrode can then be transferred into a sample containing the analyte to be quantified. For the best formation of the film bismuth must be pre-plated in a low ph condition this is because bismuth has a tendency to hydrolyse when in alkaline conditions dues to the presence of water molecule splitting. Acidic conditions catalyse this polymer degradation. Figure The molecular structure of bismuth nitrate pent hydrate In-situ plating: In this process the bismuth film is coats the electrode while the analysis process take s place. It should be noted however in order to do this the concentration of bismuth must exceed that of the analyte of interest. This is because of the possibility of interference due to saturation effects. The method of coating the electrode is superior in that it reduces experimental time as coating and analysis is done simultaneously however this method can only be performed by anodic stripping as it requires a preconcentration step. In this sense this method is not as versatile as ex-situ plating which can use any analysis method to analyse sample. Bismuth pre-cursor: A bismuth precursor can be used to modify an electrode if potential of about -0.1 V is applied onto an electrode resulting in the formation of metallic bismuth. Bi2O3(s) +3H2O+6e–2Bi(s) + 6OH– Fig The reduction reaction that takes place at the electrode between the electrode and bismuth precursor This method is usually prolific with carbon paste electrodes as it eliminates the need to use anodic stripping to form the film as well as a preplating step before for analysis of sample can take place. Bismuth modified electrode are physically and chemically stable therefore it retains its useful properties in the presence of air, moisture or heat, and under the expected conditions of application.Thus facilitate numerous measurement in different solutions without destroying the film once the electrode is coated with bismuth. This stability can be achieved by the addition of bromide ions (via sodium bromide) to the bismuth solution during the preplating stage of modification. The functionalization of conducting substrates is widely used in electroanalysis in order to confer both selectivity and sensitivity. Ion-exchange membranes are interesting materials for this purpose. Nafion will be drop casted on GCE and then positively charged ions will be incorporated within the negatively charged Nafion film. The application of suitable reduction potential allows the ions to be reduced to their metallic states. ASV will then be employed for the stripping and quantification of these ions. Cu, Zn, and Pb will be the heavy metals ions that will be examined. – chemically modified electrodes (plenty of paper in literature), then Nafion (its uses, applications and so on†¦) Electrochemistry HERE YOU CAM IMPROVE. PLEASE DESCRIBE CYCLIC VOLTAMMETRY AND WHY WE USED differential pulse voltammetry for the quantification of heavy metals Electrochemistry is associated with the analysis of chemical reactions in a solution at the boundary of an electron conductor and ionic conductors where transfer of electrons between the electrode and electrolyte take place. This electron transfer is a mechanistic description of the thermodynamic concept of redox, in which the oxidation states of both reaction partners. In general, electrochemistry deals with situations where cations transfer across from a solution –electrode interface via reaction with electrons within the interface. Anions are also transformed within this interface to produce electron, this is all through a series of oxidation and reduction reactions resulting in electrons moving from the anode connected by an external electric circuit to the cathode as a current which is carried by the ions of the supporting electrolyte. The solubility and stability of sample determines which solvent system should be used. Once this is determined compatible supporting electrolyte can be used without causing interference with the oxidation-reduction reaction. Cyclic voltammetry It enables the electrode potential to be rapidly scanned in search of redox couples. Once located, a couple can then be characterized from the potentials of peaks on the cyclic voltammogram and from changes caused by variation of the scan rate. Differential pulse voltammetry Electrochemistry has found extensive applications for the study of chemical reactions. Anodic stripping voltammetry This method of analysis which quantitatively determines the specific ionic species; the analyte of interest is electroplated on the working electrode through a deposition step. During a stripping stage the analyte is oxidised and the current is measured. The oxidation of elemental species is registered as peaks in the current signal at the potential at which the species is being oxidised. The stripping may either be linear, square, wave etc in the case of this experiment it is pulse and cyclic. Four steps of anodic stripping Cleaning: the potential is held at a oxidize state greater than that of the analyte for a period of time to remove it from the electrode. Potential held at a lower potential: The potential of the system is held sufficiently low enough to reduce the analyte and deposit it on the electrode. Deposited material spread evenly on electrode: If solid inert electrode is used this step is not needed. Working electrode is raised to a higher potential and stripping (oxidization) of the analyte as analyte is oxidised it emits electrons which are measured as current. – Reference electrode is an electrode with potential which is a) independentof analyte (or other) ions in solution; b)Independent of temperature.In case of figure 2, the electrode sensitive to hydrogen ions is an indicator electrode. Potentialof an indicator electrode depends mainly on the concentration of the analyte ions (in this case hydrogen ions). 2. Experimental determination of trace metals in the Samples 2.1. Apparatus In these experiments, a glassy carbon electrode (GCE) of 3-mm diameter was used as the working electrode with an Ag/AgCl reference electrode and a platinum counter electrode. The glassy carbon electrode was polished with alumina powder (0.3 and 05 alpha) and polishing pad. These three electrodes are used in conjunction with an ivium biopotentiostat which was interfaced with a personal computer. A conventional three-electrode cell arrangement was used for voltammetric measurements. Differential Pulse Stripping Voltammetry was performed anodically to detect trace metals. Experiment was performed at room temperature (22? C ±1) 2.2. Reagents All chemicals used in this study were of analytical reagent grade and used without further purification. Bismuth (II) nitrate pentahydry, sodium bromide, potassium hexcyanoferrate(II), copper(II)nitrate hydrate, lead(II)nitrate, hexaammineruthenium(III)chloride, iron(II)nitrate Methanol and zinc nitrate hexahydrate standard stock solutions (1000 mg/L, atomic absorption standard solution) were obtained from sigma-Aldrich. Potassium hexcyanoferrate (II) and hexaammineruthenium (III) chloride are redox mediators.0.1 M acetate buffer (pH 4.65) also obtained from sigma-Aldrich was used as supporting electrolyte. Glassy carbon was supplied by sigma-Aldrich and deionised water (18 M? cm) was used throughout. Nafion ®117 polymer from sigma-Aldrich and Bismuth (II) nitrate pentahydry was used to produce electrode films. All chemicals used in the experiment are for research and development purposes. 2.3. Electrode preparation 2.3.1 Cleaning and Setting up the GCE This involves the glassy carbon surface being polished with micro-sized abrasives in order to expose a new surface. A plastic Petri dish is prepared and a polishing pad placed into the dish. A few grams of 0.3 alpha alumina powder was placed onto the polishing pad and a solution was made by the addition of deionised water. The GCE was held at right angle to the pad, and polished in a circular motion until the GCE looked like a mirror surface. The electrode was rinsed with distilled water and air dried. Ex-situ preparation of bismuth film electrode The ex-situ bismuth film electrode was prepared by deposition of metallic bismuth onto a glassy carbon substrate electrode from 0.1M acetate buffer solution (ph 4.65) containing 100mg/L bismuth (II) nitrate pentahydry by applying a potential of -1.0V for 5mins with the biopotentiostat while the solution was stirred. Bismuth film electrode in the presence of bromide ions (sodium bromide) was prepared similarly from 0.1 M acetate buffer solution (ph 4.5) containing 50mg/L bismuth (II) and 50mg/L sodium bromide by applying a potential of 0.3V for 60s. This electrode was then transfer into a sample to analyse the analyte of interest. 2.4. Procedure Setting up the ivium biopotentiostat The ivium biopotentiostat, the computer CPU and the computer monitor are turn on at the mains. The computer is manually turned by pressing the on button on the CPU, after which the monitor will display a login screen. Once logged in the ivium soft icon on the desktop was double clicked to open the program. The parameters for the ivium biopotentiostat must be set. These settings change dependent on which method is being used. For example Differential pulse stripping voltammetry was used to quantify amount of copper in a 1 mM solution of potassium nitrate in deionised water by the following method. Click on Method and under the list of electroanalysis select Differential Pulse Stripping Voltammetry. In the Parameter Box, set the E start (V) = -0.35 and the E end (V) = 0.6 (the potential range within which the analyte is determined), Current Range =100mA, Pulse time (ms) =10, Pulse amplitude (mV) =10, E step (mV) =25, Scan rate (V/s) =0.05 and the pre-treatment Time (sec) = 300. Cyclic voltammetry was used to analyse the affect of scan rate by increasing the scan rate on Nafion modified GCE in a1mM solution of potassium nitrate in 0.1 M acetate buffer at ph 4.65 at different scan -rates : Click on Method and under the list of cyclic voltammetry select standard. In the Parameter Box, set the E start (V) = -0.4, Vertex 1(V) =0.7, Vertex 2(V) =-0.4, Current Range =1mA, E step (mV) =10 and Scan rate (V/s) =0.1. Once the settings were selected and the electrodes were connected the system was run by selecting start. The run is completed when the graph appears on the screen and the computer makes a beeping sound. The graph of results was then analysed. Preparation of a 1.0 mM Potassium chloride solution To prepare a solution of 1.0 mM potassium nitrate approximately 0.0046 g of potassium nitrate was weigh out in a clean dry weighing boat using a balance and placed into a 50 ml beaker. Solution is made up by dilution to a volume of 15ml with deionised water and mix well until the potassium chloride dissolves. Preparation of a 1.0 mM Potassium chloride and hexaamineruthenine solution To prepare a solution of 1.0 mM potassium nitrate and hexaamineruthenine approximately 0.0046 g of potassium nitrate and 0.111g of hexaamineruthenine was weigh out in a clean dry weighing boat using a balance and placed into a 50 ml beaker. Solution is made up by dilution to a volume of 15ml with deionised water and mix well until the potassium Cyclic voltammetry calculations for the effect of scan rate The cyclic voltammogram is characterized by the peak potential Ep, at which the current reaches a maximum value and by the value of the current ip. When the reduction process is reversible, the peak current is again given by the relation – Ip = 0.4463 nFA (Da) 1/2Cb – (1) With a= = at 25?C – (2) This relation results from the set of differential equations for fick’s law of diffusion. In term of adjustable parameters the peak current is given by the Randle-Sevcik equation. This equation describes the effect of scan rate on the peak current ip. The equation is given by- Ip= 2.69 ?105n3/2AD1/2Cbv1/2at 25?C– (3) Figure Cyclic voltammogram where ipc and ipa show the peak cathodic and anodic current respectively for a reversible reaction. RESULTS AND DISCUSSION Effects of scan rate The effects of Scan rate was examined by increasing the scan rate from 50mV/s to 1000mV/s for a 1 mM solution of potassium chloride + hexaamineruthenine in deionised water. As the scan rate increased the current increased The 2,4-DNPHMCPE showed increase in the peak current with increase in scan rate Figure Cyclic voltammetry of GCE in 1 mM solution of potassium chloride + hexaamineruthenine in deionised water at different scan -rates a) 1000 mV/s b) 750mV/s c)400 mV/s d)100mv/s e)50mV/s Figure Cyclic voltammetry of Nafion modified GCE in a 1 mM solution of potassium chloride + hexaamineruthenine in deionised water at different scan -rates a) 1000 mV/s b) 750mV/s c)400 mV/s d)100mv/s e)50mV/s Nafion after(04/02/2011) Figure Cyclic voltammetry of Nafion modified GCE in a 1 mM solution of potassium chloride + hexaamineruthenine in deionised water at different scan -rates a) 750 mV/s b) 400mV/s c)200 mV/s d)100mv/s e)50mV/s f)20mV/s Bismuth in acetate baseline Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of lead. a) 120 µL b) 100 µL c) 80 µLd) 40 µL Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of zinc. a) 400 µL b) 300 µL c) 200 µLd) 150 µL e) 100 µL Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of zinc. a) 600 µL b) 500 µL Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of lead. a) 120 µL b) 100 µL c) 80 µLd) 40 µL Figure Differential pulse voltammetry of GCE in a 1mM solution of potassium nitrate and deionised water different concentrations of copper (II) nitrate added. a) 750 µL b) 450 µL c) 150 µL Figure Differential pulse voltammetry Nafion modified of GCE in a 1mM solution of potassium nitrate and deionised water with different concentrations of copper (II) nitrate additions. a) 650 µL b) 450 µL c) 150 µL Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of lead. a) 120 µL b) 100 µL c) 80 µLd) 40 µL Figure Differential pulse voltammetry of bismuth modified GCE in a 0.1 M solution of acetate buffer at ph 4.65 with different concentrations of lead. a) 120 µL b) 100 µL c) 80 µLd) 40 µL Figure cyclic voltammetry of Nafion modified GCE in a1mM solution of iron (II) in 0.1 acetate buffer at ph 4.65 at different scan -rates. a) 100mV/s b) 50mV/s c) 20mV/s Figure cyclic voltammetry of Nafion modified GCE in a1mM solution of potassium nitrate in 0.1 M acetate buffer at ph 4.65 at different scan -rates. a) 100mV/s b) 50mV/s c) 20mV/s Conclusion ASA = Anodic stripping voltammetry AAS = Atomic absorption spectrometry Bi = Bismuth DME = Drop mercury electrode Reference Electrode kinetics: principles and methodology By C. H. Bamford, R. G. Compton Fundamentals of analytical chemistry, eighth edition Electrochemistry for chemists http://en.wikipedia.org/wiki/Hanging_mercury_drop_electrode http://www.chem.unep.ch/mercury/report/Chapter5.htm http://www.epa.gov/ttn/oarpg/t3/reports/volume6.pdf http://electrochem.cwru.edu/encycl/art-p01-plants.htm http://en.wikipedia.org/wiki/Electric_field http://en.wikipedia.org/wiki/Molar_concentration How to cite Determination of traces of heavy metal using anodic stripping voltammetry, Essay examples

Anthem The Process of Liberation Anthems Essay Example For Students

Anthem: The Process of Liberation Anthems Essay Anthem: The Process of Liberation Many years ago, I read my first book by Ayn Rand, Anthem. I completed the book in about four hours. At the time, I was not mature enough to fully appreciate Anthems powerful symbolism. My attitude as I read the beginning of the book was one of indifference and confusion, maturing only later into concern and vigorous interest. This experience began a new phase in my intellectual development that soon led me to read Atlas Shrugged. I then started on Ayn Rands non-fictional works. My understanding of Rands philosophical system, however, came piece by piece. There was no one instant of recognition, no single aha. Until recently, I was not fully aware that I had been affected so deeply. My progress was step-by-step and I had never looked all the way back. As I began to read Anthem for a second time, I found myself in acute pain, even at the first paragraph. I continued to read it feeling much as a person would when touring a concentration camp, for, in effect, that was exactly what I was doing. There was not one hint of levity in my mood; I do not even recall breathing. I was truly looking all the way back. At the end of chapter nine, when Equality 7-2521 is alone, in the most profound sense of the word, with his Golden One, she says slowly, We are one alone . .. and only .. . and we love you who are one alone and only, I feared I could tolerate the book no longer. I had finally understood that profound sense of loneliness and despair a person can feel when they want to say I love you, but cannot say I. I could not understand how my previous reading could have seemed so easy. I proceeded, at a forced march, all the way to chapter eleven. I had never experienced the concept of labored reading before. When I read the words, I am, I realized that I had become Equality 7-2521 and that his liberation was my liberation. At that instant, I first became aware of air rushing into my lungs, and I felt free. My grim task was over. I read the rest of the book in a state of heightened self-awareness. I felt intensely every move of my eyes, every shift of my hands, every thought and every word. Anthem enslaved me and then liberated me unfortunately, most people dont even know the difference.