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Материалы IV студенческой конференции «химия. Экология. Медицина» направления работы - страница №14/19

VI МЕДИЦИНСКИЙ ФАКУЛЬТЕТ

STANISLAO CANNIZARO AND HIS CONTRIBUTION TO THE DEVELOPMENT OF MODERN CHEMISTRY

Elias Manaseh Mwana, group 2. Scientific adviser is Olga Levashova.


Stanislao Cannizzaro, (13 July 1826 – 10 May 1910) was an Italian chemist. He is remembered today largely for the Cannizzaro reaction and for his influential role in the atomic-weight deliberations of the Karlsruhe Congress in 1860.[1]

In conjunction with F.S. Cloez (1817 – 1883) made his first contribution to chemical research, in 1851, when they prepared cyanamide by the action of ammonia on cyanogen chloride in ethereal solution. In the same year, Cannizzaro accepted an appointment at the National College of AlessandriaPiedmont as professor of physical chemistry. In Alessandria, he discovered that aromatic aldehydes are decomposed by an alcoholic solution of potassium hydroxide into a mixture of the corresponding acid and alcohol.[2] For example, benzaldehyde decomposes into benzoic acid and benzyl alcohol, the Cannizzaro reaction. The Cannizzaro reaction is a chemical reaction that involves the base-induced disproportionation of an aldehyde.

 

The oxidation product is a salt of a carboxylic acid and the reduction product is an alcohol. For aldehydes with a hydrogen atom alpha to the carbonyl, i.e. R2CHCHO, the preferred reaction is an aldol condensation, originating from deprotonation of this hydrogen. This reaction restricts the scope of the Cannizzaro reaction. [3]


In the autumn of 1855, Cannizzaro became professor of chemistry at the University of Genoa, and, after further professorships at Pisa and Naples, he accepted the chair of inorganic and organic chemistry at Palermo. There, he spent ten years studying aromatic compounds and continuing to work on amines, until in 1871 when he was appointed to the chair of chemistry at the University of Rome.

References:

[1]. Ihde, Aaron J. (1961). "The Karlsruhe Congress: A Centennial Retrospective". Journal of Chemical Education 38 (2): 83–86. Bibcode1961JChEd..38...83I. doi:10.1021/ed038p83.

[2]. Cannizzaro, S. (1853). "Ueber den der Benzoësäure entsprechenden Alkohol". Liebigs Annalen 88: 129–130.doi:10.1002/jlac.18530880114.

[3]. From http://en.wikipedia.org/wiki/Cannizzaro_reaction

[4]. From http://en.wikipedia.org/wiki/Stanislao_Cannizzaro

Dmitri Ivanovich Mendeleev’s contribution to chemistry

Ngugban Simeon Ngutor, group 2. Scientific adviser is Olga Levashova.


Mendeleev was born in the village of VerkhnieAremzyani, near Tobolsk in Siberia, to Ivan Pavlovich Mendeleev and Maria Dmitrievna Mendeleev (née Kornilieva). His grandfather was PavelMaximovichSokolov, a priest of the Russian Orthodox Church from the Tver region.

Periodic table

In 1863 there were 56 known elements with a new element being discovered at a rate of approximately one per year.

Other scientists had previously identified periodicity of elements. John Newlands described a Law of Octaves, noting their periodicity according to relative atomic weight in 1864, publishing it in 1865. His proposal identified the potential for new elements such as germanium. The concept was criticized and his innovation was not recognised by the Society of Chemists until 1887. Another person to prose a periodic table was Lothar Meyer, who published a paper in 1864 describing 28 elements classified by their valence, but with no prediction of new elements.

After becoming a teacher, Mendeleev wrote the definitive textbook of his time: Principles of Chemistry (two volumes, 1868–1870). As he attempted to classify the elements according to their chemical properties, he too noticed patterns that led him to postulate his periodic table. Mendeleev was unaware of the earlier work on periodic tables going on in the 1860s. He made the following table, and by adding additional elements following this pattern, developed his extended version of the periodic table.

On 6 March 1869, Mendeleev made a formal presentation to the Russian Chemical Society, entitled The Dependence between the Properties of the Atomic Weights of the Elements, which described elements according to both atomic weight and valence. This presentation stated that



  1. The elements, if arranged according to their atomic weight, exhibit an apparent periodicity of properties.

  2. Elements which are similar regarding their chemical properties have atomic weights which are either of nearly the same value (e.g., Pt, Ir, Os) or which increase regularly (e.g., K, Rb, Cs).

  3. The arrangement of the elements in groups of elements in the order of their atomic weights corresponds to their so-called valencies, as well as, to some extent, to their distinctive chemical properties; as is apparent among other series in that of Li, Be, B, C, N, O, and F.

  4. The elements which are the most widely diffused have small atomic weights.

  5. The magnitude of the atomic weight determines the character of the element, just as the magnitude of the molecule determines the character of a compound body.

  6. We must expect the discovery of many yet unknown elements–for example, two elements, analogous to aluminium and silicon, whose atomic weights would be between 65 and 75.

  7. The atomic weight of an element may sometimes be amended by a knowledge of those of its contiguous elements. Thus the atomic weight of tellurium must lie between 123 and 126, and cannot be 128. Here Mendeleev seems to be wrong as the "atomic mass" of tellurium (127.6) remains higher than that of iodine (126.9) as displayed on modern periodic tables, but this is due to the way atomic masses are calculated, based on a weighted average of all of an element's common isotopes, not just the one-to-one proton/neutron-ratio version of the element to which Mendeleev was referring.

  8. Certain characteristic properties of elements can be foretold from their atomic weights.

AGATE

Afolabi Timothy, group 3. Scientific adviser is Svetlana Kozub.


AGATE is a microcrystalline variety of silica, chiefly chalcedony, characterised by its fineness of grain and brightness of color. Although agates may be found in various kinds of rock, they are classically associated with volcanic rocks and can be common in certain metamorphic rocks.[1] Colorful agates and other chalcedonies were obtained over 3,000 years aMost agates occur as nodules in volcanic rocks or ancient lavas where they represent cavities originally produced by the disengagement of volatiles in the molten mass which were then filled, wholly or partially, by siliceous matter deposited in regular layers upon the walls. Agate has also been known to fill veins or cracks in volcanic or altered rock underlain by granitic intrusive masses. Such agates, when cut transversely, exhibit a succession of parallel lines, often of extreme tenuity, giving a banded appearance to the section. Such stones are known as banded agate, riband agate and striped agate.

The first deposit on the wall of a cavity, forming the "skin" of the agate, is generally a dark greenish mineral substance, like celadonitedelessite or "green earth", which are rich in iron probably derived from the decomposition of the augite in the enclosing volcanic rock. This green silicate may give rise by alteration to a brown iron oxide (limonite), producing a rusty appearance on the outside of the agate-nodule. The outer surface of an agate, freed from its matrix, is often pitted and rough, apparently in consequence of the removal of the original coating. The first layer spread over the wall of the cavity has been called the "priming", and upon this base zeolitic minerals may be deposited.



Turritella agate is formed from silicified fossil Elimia tenera (erroneously considered Turritella) shells. E. tenera are spiral freshwater gastropodshaving elongated, spiral shells composed of many whorls. Similarly, coralpetrified wood and other organic remains or porous rocks can also become agatized. Agatized coral is often referred to as Petoskey stone or agate.

Greek agate is a name given to pale white to tan colored agate found in Sicily back to 400 B.C. The Greeks used it for making jewelry and beads. Even though the stone had been around centuries and was known to both the Sumerians and the Egyptians, both who used the gem for decoration and for playing important parts in their religious ceremonies, any agate of this color from Sicily, once an ancient Greek colony, is called Greek agate.

Another type of agate is Brazilian agate, which is found as sizable geodes of layered nodules. These occur in brownish tones interlayered with white and gray. Quartz forms within these nodules, creating a striking specimen when cut opposite the layered growth axis. It is often dyed in various colors for ornamental purposes.

Other forms of agate include Lake Superior agate, carnelian agate (exhibiting reddish hues), Botswana agate, blue lace agate, plume agates, moss agate, tube agate (with visible flow channels or pinhole-sized 'tubes'), fortification agate (which exhibit little or no banding structure), fire agate (which has internal flash or 'fire', the result of a layer of clear agate over a layer of hydrothermally-deposited hematite), Mexican crazy-lace agate, which often exhibits a brightly colored, complexly banded pattern (also called Rodeo Agate and Rosetta Stone depending on who owned the mine at the time).

Industry uses agates chiefly to make ornaments such as pins, brooches, paper knives, inkstands, marbles and seals. Agate is also still used today for decorative displays, cabochons, beads, carvings and Intarsia art as well as face-polished and tumble-polished specimens of varying size and origin. Because of its hardness and ability to resist acids, agate is used to make mortars and pestles to crush and mix chemicals. Because of the high polish possible with agate it has been used for centuries for leather burnishing tools

SULFUR

Imad Mohamma, group 3. Scientific adviser is Svetlana Kozub.


Sulfur represents about 0.25 percent of our total body weight,

similar to Potassium. The body contains approximately 140 grams of sulfur, mainly in the proteins, although it is distributed in small amount in cells and tissues. Sulfur has a characteristic odor that can be smelled when hair or sheep’s wool is burned. Keratin, present in the skin hair, and nails, is particularly high in the amino acid cystine, which is found in sulfur. The di-sulfide bond in Keratin gives it greater strength.

Sulfur is present in four amino acids : methionine – an essential

amino acid ; the nonessential cystine and cystiene, which can be made from methionine ; and taurine – which is not part of body tissues but does help produce bile acid for digestion. Sulfur is also present in two B vitamins, thiamine and biotin ‘ interestingly, thiamine is important to skin and biotin to hair. Sulfur is also available as various sulfates or sulfides. But overall, Sulfur is most important as part of protein.

Sulfur has been known as the “BEAUTY MINERAL” because it

helps the complexion and skin stay clear and youthful. The hydrogen sulfide gas in onions is what causes tearing. This gas can also be made by intestinal bacteria and is absorbed by the body or released as gas with a characteristic odor

Sulfur is absorbed from the small intestine primarily as the four

sulfur containing amino acids or from sulfates in water or fruits and vegetables. It is thought that elemental sulfur is not used by the human organism. Sulfur is stored in all body cells, especially the skin, hair and nails. Excess amounts are eliminated through the urine or in the feces.




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