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| پنجشنبه سیزدهم دی 1386 - [20:5] |
(سلام خدمت شمادوستان و
شما اقاي استاد ولي پور اميدوارم از ديدين اين وبلاگ لذت برده باشيد)
| پنجشنبه سیزدهم دی 1386 - [19:41] |
| پنجشنبه سیزدهم دی 1386 - [19:40] | مطالبی از منیزیم |
Magnesium metal burns with a very bright light. The picture above shows the colour arising from adding magnesium powder to a burning mixture of potassium chlorate and sucrose. Do not attempt this reaction unless are a professionally qualified chemist and you have carried out a legally satisfactory hazard assessment.
Magnesium is an important element for plant and animal life. Chlorophylls are porphyrins based upon magnesium. The adult human daily requirement of magnesium is about 0.3 g day-1.
Magnesium can be made commercially by several processes and would not normally be made in the laboratory because of its ready availability. There are massive amounts of magnesium in seawater. This can be recovered as magnesium chloride, MgCl2 through reaction with calcium oxide, CaO.
CaO + H2O → Ca2+ + 2OH-
Mg2+ + 2OH- → Mg(OH)2
Mg(OH)2 + 2HCl → MgCl2 + 2H2O
Electrolysis of hot molten MgCl2 affords magnesium as a liquid whih is poured off and chlorine gas.
cathode: Mg2+(l) + 2e- → Mg anode: Cl-(l) → 1/2Cl2 (g) + e-
The other methos used to produce magnesium is non electrolytic and involves dolomite, [MgCa(CO3)2], an important magnesium mineral. This is "calcined" by heating to form calcined dolomite, MgO.CaO, and this reacted with ferrosilicon alloy.
2[MgO.CaO] + FeSi → 2Mg + Ca2SiO4 + Fe
| پنجشنبه سیزدهم دی 1386 - [19:21] |
Potency
The LD50 for pure arsenic is 763 mg/kg (by ingestion) and 13 mg/kg (by intraperitoneal injection). For a 70 kg (~155 lb) human, this works out to about 53 grams (less than 2 ounces). However, compounds containing arsenic can be significantly more toxic.[2]
Nearly all reported arsenic poisonings were not caused by pure arsenic, but by arsenic-oxygen compounds, especially arsenic trioxide, which is approximately 500 times more toxic than pure arsenic, and by arsine.
In addition to its use as a poison, arsenic was used medicinally for centuries and was used extensively to treat syphilis before penicillin was introduced. Arsenic was replaced as a therapeutic agent by sulfa drugs and then by antibiotics. Arsenic was also an ingredient in many tonics (or "patent medicines"). In addition, during the Victorian era, some women used a mixture of vinegar, chalk, and arsenic applied topically to whiten their skin. The use of arsenic was intended to prevent aging and creasing of the skin, but some arsenic was inevitably absorbed into the blood stream.
Some pigments, most notably the popular Emerald Green (known also under several other names), were based on arsenic compounds. Overexposure to these pigments was a frequent cause of accidental poisoning of artists and craftsmen.
Chronic arsenic poisoning results from drinking water with high levels of arsenic over a long period of time. This may occur due to arsenic contamination of groundwater. [3]
Effects include changes in skin color, formation of hard patches on the skin, skin cancer, lung cancer, cancer of the kidney and bladder, and can lead to gangrene. The World Health Organization recommends a limit of 0.01 mg/L (10ppb) of arsenic in drinking water. This recommendation was established based on the limit of detection of available testing equipment at the time of publication of the WHO water quality guidelines. More recent findings show that consumption of water with levels as low as 0.00017mg/L (0.17ppb) over long periods of time can lead to arsenicosis.
Non-carcinogenic chronic effects include liver injury—jaundice and cirrhosis;—peripheral vascular disease involving blueness of the extremities; Raynaud's syndrome; blackfoot disease (a type of gangrene); anemia, resulting from impaired heme biosynthesis; and hyperkeratosis of the skin.
There are also multiple lines of evidence for the carcinogenic effects of arsenic.
Arsenic has been known to cause many problems in Third World countries where groundwater supplies have been contaminated by arsenic derived from geologically recent fluvial deposits containing arseno-pyrites. This is a particular problem in Bangladesh where tube wells installed since the 1970s have intercepted ground waters flowing in the fluvial deposits. Concentrations in these wells can exceed 1 part per thousand whereas the WHO maximum level is 10 parts per billion. See Arsenic contamination of groundwater.
Roger Smith, Professor of Pharmacology and Toxicology Emeritus, Dartmouth Medical School [1], [2], has confirmed that natural arsenic contamination of drinking water has also been a problem in wells in New Hampshire. Chronic low-level arsenic poisoning, or arsenicosis, as is seen in Bangladesh, can potentially cause cancer.
In the 700s, an Arab alchemist named Jabir became the first to prepare arsenic trioxide, a white, tasteless, odorless powder. Jabir's preparation seemed the ideal poison as it left no traceable (at the time) elements in the body.
Arsenic became a favorite murder weapon of the Middle Ages and Renaissance, particularly among ruling classes in Italy, notably the Borgias. Because the symptoms are similar to those of cholera, which was common at the time, arsenic poisoning often went undetected. By the 19th C., it had acquired the nickname "inheritance powder," perhaps because impatient heirs were known or suspected to use it to ensure or accelerate their inheritances. Elizabeth Báthory is also suspected of having used arsenic to poison male lovers so that they could never leave her, probably as a result of her first husband having an affair.
On April 27, 2003, sixteen members of the Gustaf Adolph Lutheran Church in New Sweden, Maine, became ill following the church coffee hour; one died a short time later. Investigation revealed that the coffee had been heavily laced with arsenic. As of the publication of Christine Ellen Young's A Bitter Brew in 2005, no one had been formally charged with the crime.
Murder mystery stories often feature arsenic poisoning, although they commonly omit the more disagreeable symptoms.
Arsenic poisoning, accidental or deliberate, has been implicated in the illness and death of a number of prominent people throughout history.
Recent forensic evidence uncovered by Italian scientists suggests that Francesco and his wife were poisoned possibly by his brother and successor Fernando.[4]
George III's (1738 – 1820) personal health was a concern throughout his long reign. He suffered from periodic episodes of physical and mental illness, five of them disabling enough to require the King to withdraw from his duties. In 1969, researchers asserted that the episodes of madness and other physical symptoms were characteristic of the disease porphyria, which was also identified in members of his immediate and extended family. In addition, a 2004 study of samples of the King's hair[5] revealed extremely high levels of arsenic, which is a possible trigger of disease symptoms. A 2005 article in the medical journal The Lancet[6] suggested the source of the arsenic could be the antimony used as a consistent element of the King's medical treatment. The two minerals are often found in the same ground, and mineral extraction at the time was not precise enough to eliminate arsenic from compounds containing antimony.
There is a theory that Napoleon Bonapart (1769 – 1821) suffered and died from arsenic poisoning during his imprisonment on the island of Saint Helena. Forensic samples of his hair did show high levels, 13 times the normal amount, of the element. This, however, does not prove deliberate poisoning by Napoleon's enemies: copper arsenite has been used as a pigment in some wallpapers, and microbiological liberation of the arsenic into the immediate environment would be possible. The case is equivocal in the absence of clearly authenticated samples of the wallpaper. As Napoleon's body lay for nearly 20 years in a grave on the island, before being moved to its present resting place in Paris, arsenic from the soil could also have polluted the sample. Even without contaminated wallpaper or soil, commercial use of arsenic at the time provided many other routes by which Napoleon could have consumed enough arsenic to leave this forensic trace.
American explorer Charles Francis Hall (1821-1871) died unexpectedly during his third Arctic expedition aboard the ship Polaris. After returning to the ship from a sledging expedition Hall drank a cup of coffee and fell violently ill. He collapsed in what was described as a fit. He suffered from vomiting and delirium for the next week, then seemed to improve for a few days. He accused several of the ship's company, including ship's physician Dr. Emil Bessels with whom he had longstanding disagreements, of having poisoned him. Shortly thereafter, Hall again began suffering the same symptoms, died, and was taken ashore for burial. Following the expedition's return a US Navy investigation ruled that Hall had died from apoplexy.
In 1968, however, Hall's biographer Chauncey C. Loomis, a professor at Dartmouth College, traveled to Greenland to exhume Hall's body. Due to the permafrost, Hall's body, flag shroud, clothing and coffin were remarkably well preserved. Tissue samples of bone, fingernails and hair showed that Hall died of poisoning from large doses of arsenic in the last two weeks of his life, consistent with the symptoms party members reported. It is possible that Hall dosed himself with quack medicines which included the poison, but it is more likely that he was murdered by Dr. Bessels or one of the other members of the expedition.
Huo Yuan J made his name as a Chinese martial artist. He was poisoned in 1910 during his fight with the Japanese, who accused Chinese men to be "sick man of Asia". Although no initial evidence was found, the police later discovered that there were black spots in his pelvis, thus confirming it was arsenic that had poisoned him[citation needed].
A later case of arsenic poisoning is that of Clare Boothe Luce, (1903 – 1987) the American ambassador to Italy in the years just following World War II. Although she did not die from her poisoning, she suffered an increasing variety of physical and psychological symptoms until arsenic poisoning was diagnosed, and its source traced to the old, arsenic-laden flaking paint on the ceiling of her bedroom. Another source (see below) explains her poisoning as resulting from eating food contaminated by flaking of the ceiling of the embassy dining room.
Emerald Green, a pigment frequently used by Impressionist painters, is based on arsenic. Cezanne developed severe diabetes, which is a symptom of chronic arsenic poisoning. Monet's blindness and Van Gogh's neurological disorders could have been partially due to their use of Emerald Green. Poisoning by other commonly used substances, including liquor and absinthe, lead pigments, mercury-based Vermilion, and solvents such as turpentine, could also be a factor in these cases.
| پنجشنبه سیزدهم دی 1386 - [19:10] |
Comprehensive data on the chemical element Arsenic is provided on this page; including scores of properties, element names in many languages, most known nuclides of Arsenic. Common chemical compounds are also provided for many elements. In addition technical terms are linked to their definitions and the menu contains links to related articles that are a great aid in one studies. Using the "Periodic Table of Elements Quick Navigation" graphic at the bottom of the sidebar menu, one can quickly jump from chemical element to chemical element.
| پنجشنبه سیزدهم دی 1386 - [19:3] |
Arsenic is a natural element found in soil and minerals. Arsenic compounds are used to preserve wood, as pesticides, and in some industries. Arsenic can get into air, water, and the ground from wind-blown dust. It may also get into water from runoff.
You may be exposed to arsenic by
Exposure to arsenic can cause many health problems. Being exposed to low levels for a long time can change the color of your skin. It can cause corns and small warts. Exposure to high levels of arsenic can cause death.
| پنجشنبه سیزدهم دی 1386 - [19:0] |
This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.
Elemental arsenic occurs in two solid modifications: yellow, and grey or metallic, with specific gravities of 1.97, and 5.73, respectively. The element is a steel grey, very brittle, crystalline, semimetallic (metalloid) solid. It tarnishes in air, and when heated rapidly oxidises to arsenous oxide which has a garlic odour.
Arsenic and its compounds are poisonous as any reader of "who-done-it" books knows. Upon heating arsenic and some minerals containing arsenic, it sublimes (transfers from the solid to the gaseous state, without passing through the liquid state).
It is not usually necessary to make arsenic in the laboratory as it is commercially available. Arsenic is found in nature in a number of minerals including realgar (As4S4), orpiment (As2S3), arsenolite (As2O3), and iron minerals such as arsenopyrite (FeAsS) and loellingite (FeAs2). Arsenic is made on an industrial scale by heating appropriate minerals in the absence of air. The arsenic is condensed out as a solid.
FeAsS (700°C) → FeS + As(g) → As(s)
| پنجشنبه سیزدهم دی 1386 - [18:40] |
| پنجشنبه سیزدهم دی 1386 - [18:38] |
Breathing high levels of inorganic arsenic can give you a sore throat or irritated lungs.
Ingesting very high levels of arsenic can result in death. Exposure to lower levels can cause nausea and vomiting, decreased production of red and white blood cells, abnormal heart rhythm, damage to blood vessels, and a sensation of “pins and needles” in hands and feet.
Ingesting or breathing low levels of inorganic arsenic for a long time can cause a darkening of the skin and the appearance of small “corns” or “warts” on the palms, soles, and torso.
Skin contact with inorganic arsenic may cause redness and swelling.
Almost nothing is known regarding health effects of organic arsenic compounds in humans. Studies in animals show that some simple organic arsenic compounds are less toxic than inorganic forms. Ingestion of methyl and dimethyl compounds can cause diarrhea and damage to the kidneys.
Several studies have shown that ingestion of inorganic arsenic can increase the risk of skin cancer and cancer in the liver, bladder, and lungs. Inhalation of inorganic arsenic can cause increased risk of lung cancer. The Department of Health and Human Services (DHHS) and the EPA have determined that inorganic arsenic is a known human carcinogen. The International Agency for Research on Cancer (IARC) has determined that inorganic arsenic is carcinogenic to humans.
There is some evidence that long-term exposure to arsenic in children may result in lower IQ scores. There is also some evidence that exposure to arsenic in the womb and early childhood may increase mortality in young adults.
There is some evidence that inhaled or ingested arsenic can injure pregnant women or their unborn babies, although the studies are not definitive. Studies in animals show that large doses of arsenic that cause illness in pregnant females, can also cause low birth weight, fetal malformations, and even fetal death. Arsenic can cross the placenta and has been found in fetal tissues. Arsenic is found at low levels in breast milk.
There are tests available to measure arsenic in your blood, urine, hair, and fingernails. The urine test is the most reliable test for arsenic exposure within the last few days. Tests on hair and fingernails can measure exposure to high levels of arsenic over the past 6-12 months. These tests can determine if you have been exposed to above-average levels of arsenic. They cannot predict whether the arsenic levels in your body will affect your health.
The EPA has set limits on the amount of arsenic that industrial sources can release to the environment and has restricted or cancelled many of the uses of arsenic in pesticides. EPA has set a limit of 0.01 parts per million (ppm) for arsenic in drinking water.
The Occupational Safety and Health Administration (OSHA) has set a permissible exposure limit (PEL) of 10 micrograms of arsenic per cubic meter of workplace air (10 μg/m3) for 8 hour shifts and 40 hour work weeks.
Agency for Toxic Substances and Disease Registry (ATSDR). 2007. Toxicological Profile for Arsenic (Update). Atlanta, GA: U.S. Department of Health and Human Services, Public Health Service.
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