An acid–base reaction is a chemical reaction that occurs between an acid and a base. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called acid–base theories, for example, Brønsted–Lowry acid–base theory. Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The first of these concepts was provided by the French chemist Antoine Lavoisier, around 1776.[1]
Saturday, July 25, 2015
Acid Base Reaction - College Education
An acid–base reaction is a chemical reaction that occurs between an acid and a base. Several theoretical frameworks provide alternative conceptions of the reaction mechanisms and their application in solving related problems; these are called acid–base theories, for example, Brønsted–Lowry acid–base theory. Their importance becomes apparent in analyzing acid–base reactions for gaseous or liquid species, or when acid or base character may be somewhat less apparent. The first of these concepts was provided by the French chemist Antoine Lavoisier, around 1776.[1]
Precipitation Reactions
Precipitation is the creation of a solid from a solution. When the reaction occurs in a liquid solution, the solid formed is called the 'precipitate'. The chemical that causes the solid to form is called the 'precipitant'. Without sufficient force of gravity (settling) to bring the solid particles together, the precipitate remains in suspension. After sedimentation, especially when using a centrifuge to press it into a compact mass, the precipitate may be referred to as a 'pellet'. The precipitate-free liquid remaining above the solid is called the 'supernate' or 'supernatant'. Powders derived from precipitation have also historically been known as 'flowers'.
Sometimes the formation of a precipitate indicates the occurrence of a chemical reaction. If silver nitrate solution is poured into a solution of sodium chloride, a chemical reaction occurs forming a white precipitate of silver chloride. When potassium iodide solution reacts with lead nitrate solution, a yellow precipitate of lead iodide is formed.
Precipitation may occur if the concentration of a compound exceeds its solubility (such as when mixing solvents or changing their temperature). Precipitation may occur rapidly from a supersaturated solution.
In solids, precipitation occurs if the concentration of one solid is above the solubility limit in the host solid, due to e.g. rapid quenching or ion implantation, and the temperature is high enough that diffusion can lead to segregation into precipitates. Precipitation in solids is routinely used to synthesize nanoclusters.[1]
An important stage of the precipitation process is the onset of nucleation. The creation of a hypothetical solid particle includes the formation of an interface, which requires some energy based on the relative surface energy of the solid and the solution. If this energy is not available, and no suitable nucleation surface is available, supersaturation occurs.
Redox Reactions
Redox is a contraction of the name for chemical reduction-oxidation reaction. A reduction reaction always occurs with an oxidation reaction. Redox reactions include all chemical reactions in which atoms have their oxidation state changed; in general, redox reactions involve the transfer of electrons between chemical species. The chemical species from which the electron is stripped is said to have been oxidized, while the chemical species to which the electron is added is said to have been reduced. Oxygen is not necessarily included in such reactions as other chemical species can serve the same function.
The term "redox" comes from two concepts involved with electron transfer: reduction and oxidation.[1] It can be explained in simple terms:
Although oxidation reactions are commonly associated with the formation of oxides from oxygen molecules, these are only specific examples of a more general concept of reactions involving electron transfer.
Wednesday, July 22, 2015
Saturday, July 18, 2015
Zinc and Sulfur - Periodic Table of Videos
Zinc is a chemical element with symbol Zn and atomic number 30. It is the first element of group 12 of the periodic table. In some respects zinc is chemically similar to magnesium: its ion is of similar size and its only common oxidation state is +2. Zinc is the 24th most abundant element in Earth's crust and has five stable isotopes. The most common zinc ore is sphalerite (zinc blende), a zinc sulfide mineral. The largest mineable amounts are found in Australia, Asia, and the United States. Zinc production includes froth flotation of the ore, roasting, and final extraction using electricity (electrowinning).
Sulfur or sulphur (see spelling differences) is a chemical element with symbol S and atomic number 16. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow crystalline solid at room temperature. Chemically, sulfur reacts with all elements except for nitrogen and the noble gases.
Chromium Trioxide - Periodic Table of Videos
Chromium trioxide is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name.[6] This compound is a dark-purple solid under anhydrous conditions, bright orange when wet and which dissolves in water concomitant with hydrolysis. Millions of kilograms are produced annually, mainly for electroplating.[7] Chromium trioxide is a powerful oxidiser and a suspected carcinogen.Chromium trioxide is mainly used in chrome plating. It is typically employed with additives that affect the plating process but do not react with the trioxide. The trioxide reacts with cadmium, zinc, and other metals to generate passivating chromate films that resist corrosion. It is also used in the production of synthetic rubies. Chromic acid solution is also used in applying types of anodic coating to aluminium, which are primarily used in aerospace applications. A Chromic Acid/ Phosphoric Acid solution is also the preferred stripping agent of anodic coatings of all types.
Calcium Carbide & Acetylene - Periodic Table of Videos
Calcium carbide is a chemical compound with the chemical formula of CaC2. Its main use industrially is in the production of acetylene and calcium cyanamide.[3]
The pure material is colorless, however pieces of technical-grade calcium carbide are grey or brown and consist of about 80–85% of CaC2 (the rest is CaO (calcium oxide), Ca3P2 (calcium phosphide), CaS (calcium sulfide), Ca3N2 (calcium nitride), SiC (silicon carbide), etc.). In the presence of trace moisture, technical-grade calcium carbide emits an unpleasant odor reminiscent of garlic.[4]
Applications of calcium carbide include manufacture of acetylene gas, and for generation of acetylene in carbide lamps; manufacture of chemicals for fertilizer; and in steelmaking.
Acetylene (systematic name: ethyne) is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne.[4] This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure form and thus is usually handled as a solution.[5] Pure acetylene is odorless, but commercial grades usually have a marked odor due to impurities.[6]
As an alkyne, acetylene is unsaturated because its two carbon atoms are bonded together in a triple bond. The carbon–carbon triple bond places all four atoms in the same straight line, with CCH bond angles of 180°.
Copper Chloride - Periodic Table of Videos
Copper chloride is the chemical compound with the chemical formula CuCl2. This is a light brown solid, which slowly absorbs moisture to form a blue-green dihydrate. The copper(II) chlorides are some of the most common copper(II) compounds, after copper sulfate.
Anhydrous CuCl2 adopts a distorted cadmium iodide structure. In this motif, the copper centers are octahedral. Most copper(II) compounds exhibit distortions from idealized octahedral geometry due to the Jahn-Teller effect, which in this case describes the localization of one d-electron into a molecular orbital that is strongly antibonding with respect to a pair of chloride ligands. In CuCl2·2H2O, the copper again adopts a highly distorted octahedral geometry, the Cu(II) centers being surrounded by two water ligands and four chloride ligands, which bridge asymmetrically to other Cu centers.[2]
Copper(II) chloride is paramagnetic. Of historical interest, CuCl2·2H2O was used in the first electron paramagnetic resonance measurements by Yevgeny Zavoisky in 1944.[3][4]
Radioactive Alcohol - Periodic Table of Videos
Ethanol is thought to cause harm partly as a result of direct damage to DNA caused by its metabolites.[9]
Tertiary alcohols cannot be metabolized into aldehydes[17] and as a result they cause no hangover or toxicity through this mechanism.
Some secondary and tertiary alcohols are less poisonous than ethanol, because the liver is unable to metabolize them into toxic by-products.[18] This makes them more suitable for pharmaceutical use as the chronic harms are lower.[19] Ethchlorvynol and tert-amyl alcohol are tertiary alcohols which have seen both medicinal and recreational use.[20]
Other alcohols are substantially more poisonous than ethanol, partly because they take much longer to be metabolized and partly because their metabolism produces substances that are even more toxic. Methanol (wood alcohol), for instance, is oxidized to formaldehyde and then to the poisonous formic acid in the liver by alcohol dehydrogenase and formaldehyde dehydrogenase enzymes, respectively; accumulation of formic acid can lead to blindness or death.[21] Likewise, poisoning due to other alcohols such as ethylene glycol or diethylene glycol are due to their metabolites, which are also produced by alcohol dehydrogenase.[22][23]
Methanol itself, while poisonous (LD50 5628 mg/kg, oral, rat[24]), has a much weaker sedative effect than ethanol.
Isopropyl alcohol is oxidized to form acetone by alcohol dehydrogenase in the liver, but has occasionally been abused by alcoholics, leading to a range of adverse health effects.[25]
Alcohol - Periodic Table of Videos
In chemistry, an alcohol is any organic compound in which the hydroxyl functional group (–OH) is bound to a saturated carbon atom.[2] The term alcohol originally referred to the primary alcohol ethanol (ethyl alcohol), the predominant alcohol in alcoholic beverages.
The suffix -ol appears in the IUPAC chemical name of all substances where the hydroxyl group is the functional group with the highest priority; in substances where a higher priority group is present the prefix hydroxy- will appear in the International Union of Pure and Applied Chemistry (IUPAC) name. The suffix -ol in non-systematic names (such as paracetamol or cholesterol) also typically indicates that the substance includes a hydroxyl functional group and, so, can be termed an alcohol. But many substances, particularly sugars (examples glucose and sucrose) contain hydroxyl functional groups without using the suffix. An important class of alcohols, of which methanol and ethanol are the simplest members is the saturated straight chain alcohols, the general formula for which is CnH2n+1OH.
In other less formal contexts, an alcohol is often called with the name of the corresponding alkyl group followed by the word "alcohol", e.g., methyl alcohol, ethyl alcohol. Propyl alcohol may be n-propyl alcohol or isopropyl alcohol, depending on whether the hydroxyl group is bonded to the end or middle carbon on the straight propane chain. As described under systematic naming, if another group on the molecule takes priority, the alcohol moiety is often indicated using the "hydroxy-" prefix.
Alcohols are then classified into primary, secondary (sec-, s-), and tertiary (tert-, t-), based upon the number of carbon atoms connected to the carbon atom that bears the hydroxyl functional group. (The respective numeric shorthands 1°, 2°, and 3° are also sometimes used in informal settings.[31]) The primary alcohols have general formulas RCH2OH; methanol (CH3OH is the simplest primary alcohol (R=H), and after it, ethanol (R=CH3). Secondary alcohols can be referred to with the shorthand RR'CHOH; 2-propanol is the simplest example (R=R'=CH3). Tertiary alcohols can be referred to with the shorthand RR'R"COH; tert-butanol (2-methylpropan-2-ol) is the simplest example (R=R'=R"=CH3). In these shorthands, R, R', and R" represent substituents, alkyl or other attached, generally organic groups
Magnetic Uranium - Periodic Table of Videos
When refined, uranium is a silvery white, weakly radioactive metal. It has a Mohs hardness of 6, sufficient to scratch glass and approximately equal to that of titanium, rhodium, manganese and niobium. It is malleable, ductile, slightly paramagnetic, strongly electropositive and a poor electrical conductor.[9][10] Uranium metal has a very high density of 19.1 g/cm3,[11] denser than lead (11.3 g/cm3),[12] but slightly less dense than tungsten and gold (19.3 g/cm3).[13][14]
Uranium metal reacts with almost all non-metal elements (with an exception of the noble gases) and their compounds, with reactivity increasing with temperature.[15] Hydrochloric and nitric acids dissolve uranium, but non-oxidizing acids other than hydrochloric acid attack the element very slowly.[9] When finely divided, it can react with cold water; in air, uranium metal becomes coated with a dark layer of uranium oxide.[10] Uranium in ores is extracted chemically and converted into uranium dioxide or other chemical forms usable in industry.
Uranium-235 was the first isotope that was found to be fissile. Other naturally occurring isotopes are fissionable, but not fissile. On bombardment with slow neutrons, its uranium-235 isotope will most of the time divide into two smaller nuclei, releasing nuclear binding energy and more neutrons. If too many of these neutrons are absorbed by other uranium-235 nuclei, a nuclear chain reaction occurs that results in a burst of heat or (in special circumstances) an explosion. In a nuclear reactor, such a chain reaction is slowed and controlled by a neutron poison, absorbing some of the free neutrons. Such neutron absorbent materials are often part of reactor control rods (see nuclear reactor physics for a description of this process of reactor control).
Chemistry of Concrete - Periodic Table of Videos
Concrete is a composite material composed of coarse aggregate bonded together with a fluid cement which hardens over time. Most concretes used are lime-based concretes such as Portland cement concrete or concretes made with other hydraulic cements, such as ciment fondu. However, road surfaces are also a type of concrete, asphalt concrete, where the cement material is bitumen, and polymer concretes are sometimes used where the cementing material is a polymer.
In Portland cement concrete (and other hydraulic cement concretes), when the aggregate is mixed together with the dry cement and water, they form a fluid mass that is easily molded into shape. The cement reacts chemically with the water and other ingredients to form a hard matrix which binds all the materials together into a durable stone-like material that has many uses.[2] Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix or the finished material. Most concrete is poured with reinforcing materials (such as rebar) embedded to provide tensile strength, yielding reinforced concrete.
Famous concrete structures include the Hoover Dam, the Panama Canal and the Roman Pantheon. The earliest large-scale users of concrete technology were the ancient Romans, and concrete was widely used in the Roman Empire. The Colosseum in Rome was built largely of concrete, and the concrete dome of the Pantheon is the world's largest unreinforced concrete dome.[3] Today, large concrete structures (for example, dams and multi-storey car parks) are usually made with reinforced concrete.
After the Roman Empire collapsed, use of concrete became rare until the technology was redeveloped in the mid-18th century. Today, concrete is the most widely used man-made material (measured by tonnage).
Carvone (Spearmint) - Periodic Table of Videos
Carvone is a member of a family of chemicals called terpenoids.[2] Carvone is found naturally in many essential oils, but is most abundant in the oils from seeds of caraway (Carum carvi), spearmint (Mentha spicata), and dill.[3]
Carvone forms two mirror image forms or enantiomers: R-(–)-carvone smells like spearmint leaves. Its mirror image, S-(+)-carvone, smells like caraway seeds.[4] The fact that the two enantiomers are perceived as smelling different is evidence that olfactory receptors must contain chiral groups, allowing them to respond more strongly to one enantiomer than to the other. Not all enantiomers have distinguishable odors. Squirrel monkeys have also been found to be able to discriminate between carvone enantiomers.[5]
The two forms are also referred to by the older names of laevo (L) referring to R-(–)-carvone, and dextro (D) referring to S-(+)-carvone.
Methane - Periodic Table of Videos
Methane (/ˈmɛθeɪn/ or /ˈmiːθeɪn/) is a chemical compound with the chemical formula CH4 (one atom of carbon and four atoms of hydrogen). It is the simplest alkane and the main component of natural gas. The relative abundance of methane on Earth makes it an attractive fuel, though capturing and storing it poses challenges due to its gaseous state under at normal conditions for temperature and pressure.
In its natural state, methane is found both below ground and under the sea floor. When it finds its way to the surface and the atmosphere, it is known as atmospheric methane.[5] The Earth's atmospheric methane concentration has increased by about 150% since 1750, and it accounts for 20% of the total radiative forcing from all of the long-lived and globally mixed greenhouse gases (these gases don't include water vapor which is by far the largest component of the greenhouse effect).[6] Methane breaks down in the atmosphere and creates CH·3 with water vapor.
Methane is a tetrahedral molecule with four equivalent C–H bonds. Its electronic structure is described by four bonding molecular orbitals (MOs) resulting from the overlap of the valence orbitals on C and H. The lowest energy MO is the result of the overlap of the 2s orbital on carbon with the in-phase combination of the 1s orbitals on the four hydrogen atoms. Above this energy level is a triply degenerate set of MOs that involve overlap of the 2p orbitals on carbon with various linear combinations of the 1s orbitals on hydrogen. The resulting "three-over-one" bonding scheme is consistent with photoelectron spectroscopic measurements.
At room temperature and standard pressure, methane is a colorless, odorless gas.[9] The familiar smell of natural gas as used in homes is achieved by the addition of an odorant, usually blends containing tert-butylthiol, as a safety measure. Methane has a boiling point of −161 °C (−257.8 °F) at a pressure of one atmosphere.[10] As a gas it is flammable over a range of concentrations (4.4–17%) in air at standard pressure.
Solid methane exists in several modifications. Presently nine are known.[11] Cooling methane at normal pressure results in the formation of methane I. This substance crystallizes in the cubic system (space group Fm3m). The positions of the hydrogen atoms are not fixed in methane I, i.e. methane molecules may rotate freely. Therefore, it is a plastic crystal.[12]
Carbon Dioxide - Periodic Table of Videos
Carbon dioxide (chemical formula CO2) is a colorless and odorless gas vital to life on Earth. This naturally occurring chemical compound is composed of a carbon atom covalently double bonded to two oxygen atoms. Carbon dioxide exists in Earth's atmosphere as a trace gas at a concentration of about 0.04 percent (400 ppm) by volume.[3] Natural sources include volcanoes, hot springs and geysers and it is freed from carbonate rocks by dissolution in water and acids. Because carbon dioxide is soluble in water, it occurs naturally in groundwater, rivers and lakes, in ice caps and glaciers and also in seawater. It is present in deposits of petroleum and natural gas.[4]
Atmospheric carbon dioxide is the primary source of carbon in life on Earth and its concentration in Earth's pre-industrial atmosphere since late in the Precambrian was regulated by photosynthetic organisms and geological phenomena. As part of the carbon cycle, plants, algae, and cyanobacteria use light energy to photosynthesize carbohydrate from carbon dioxide and water, with oxygen produced as a waste product.[5]
Carbon dioxide (CO2) is produced by all aerobic organisms when they metabolize carbohydrate and lipids to produce energy by respiration.[6] It is returned to water via the gills of fish and to the air via the lungs of air-breathing land animals, including humans. Carbon dioxide is produced during the processes of decay of organic materials and the fermentation of sugars in bread, beer and winemaking. It is produced by combustion of wood, carbohydrates and fossil fuels such as coal, peat, petroleum and natural gas.
It is a versatile industrial material, used, for example, as an inert gas in welding and fire extinguishers, as a pressurizing gas in air guns and oil recovery, as a chemical feedstock and in liquid form as a solvent in decaffeination of coffee and supercritical drying. It is added to drinking water and carbonated beverages including beer and sparkling wine to add effervescence. The frozen solid form of CO2, known as "dry ice" is used as a refrigerant and as an abrasive in dry-ice blasting.
Carbon dioxide is an important greenhouse gas. Burning of carbon-based fuels since the industrial revolution has rapidly increased its concentration in the atmosphere, leading to global warming. It is also a major cause of ocean acidification because it dissolves in water to form carbonic acid.[7]
Benzene - Periodic Table of Videos
Benzene is an important organic chemical compound with the chemical formula C6H6. The benzene molecule is composed of 6 carbon atoms joined in a ring with 1 hydrogen atom attached to each. Because it contains only carbon and hydrogen atoms, benzene is classed as a hydrocarbon.
Benzene is a natural constituent of crude oil and is one of the elementary petrochemicals. Because of the cyclic continuous pi bond between the carbon atoms, benzene is classed as an aromatic hydrocarbon, the second [n]-annulene ([6]-annulene. It is sometimes abbreviated Ph–H. Benzene is a colorless and highly flammable liquid with a sweet smell. It is used primarily as a precursor to the manufacture of chemicals with more complex molecules, such as ethylbenzene and cumene, of which billions of kilograms are produced. Because benzene has a high octane number, it is an important component of gasoline.
Because benzene is a human carcinogen, most non-industrial applications have been limited.
The empirical formula for benzene was long known, but its highly polyunsaturated structure, with just one hydrogen atom for each carbon atom, was challenging to determine. Archibald Scott Couper in 1858 and Joseph Loschmidt in 1861[28] suggested possible structures that contained multiple double bonds or multiple rings, but too little evidence was then available to help chemists decide on any particular structure.
In 1865, the German chemist Friedrich August Kekulé published a paper in French (for he was then teaching in Francophone Belgium) suggesting that the structure contained a ring of six carbon atoms with alternating single and double bonds. The next year he published a much longer paper in German on the same subject.[29][30] Kekulé used evidence that had accumulated in the intervening years—namely, that there always appeared to be only one isomer of any monoderivative of benzene, and that there always appeared to be exactly three isomers of every disubstituted derivative—now understood to correspond to the ortho, meta, and para patterns of arene substitution—to argue in support of his proposed structure.[31] Kekulé's symmetrical ring could explain these curious facts, as well as benzene's 1:1 carbon-hydrogen ratio.[32]
Sulfuric Acid - Periodic Table of Videos
Sulfuric acid (alternative spelling sulphuric acid) is a highly corrosive strong mineral acid with the molecular formula H2SO4 and molecular weight 98.079 g/mol. It is a pungent-ethereal, colorless to slightly yellow viscous liquid that is soluble in water at all concentrations.[6] Sometimes, it is dyed dark brown during production to alert people to its hazards.[7] The historical name of this acid is oil of vitriol.[8]
Sulfuric acid is a diprotic acid and shows different properties depending upon its concentration. Its corrosiveness on other materials, like metals, living tissues or even stones, can be mainly ascribed to its strong acidic nature and, if concentrated, strong dehydrating and oxidizing properties. Sulfuric acid at a high concentration can cause very serious damage upon contact, since not only does it cause chemical burns via hydrolysis, but also secondary thermal burns through dehydration.[9][10] It can lead to permanent blindness if splashed onto eyes and irreversible damage if swallowed.[9] Accordingly, safety precautions should be strictly observed when handling it. Moreover, it is hygroscopic, readily absorbing water vapour from the air.[6]
Sulfuric acid has a wide range of applications including domestic acidic drain cleaner,[11] electrolyte in lead-acid batteries and various cleaning agents. It is also a central substance in the chemical industry. Principal uses include mineral processing, fertilizer manufacturing, oil refining, wastewater processing, and chemical synthesis. It is widely produced with different methods, such as contact process, wet sulfuric acid process and some other methods.
Super Expensive Metals - Periodic Table of Videos
A precious metal is a rare, naturally occurring metallic chemical element of high economic value. Chemically, the precious metals tend to be less reactive than most elements (see noble metal). They are usually ductile and have a high lustre. Historically, precious metals were important as currency but are now regarded mainly as investment and industrial commodities. Gold, silver, platinum, and palladium each have an ISO 4217 currency code.
The best-known precious metals are the coinage metals, gold and silver. Although both have industrial uses, they are better known for their uses in art, jewellery, and coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded.[1] The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Historically, precious metals have commanded much higher prices than common industrial metals.
Can you drink Heavy Water?
Heavy water (deuterium oxide (2H
2O )) is a form of water that contains a larger than normal amount of the hydrogen isotope deuterium (2H or D, also known as heavy hydrogen), rather than the common hydrogen-1 isotope (1H or H, also called protium) that makes up most of the hydrogen in normal water.[3]
A molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary "light" water. The weight of a heavy water molecule, however, is not substantially different from that of a normal water molecule, because about 89% of the molecular weight of water comes from the single oxygen atom rather than the two hydrogen atoms. The colloquial term heavy water refers to a highly enriched water mixture that contains mostly deuterium oxide (D2O), but also some hydrogen-deuterium oxide (HDO) and a smaller number of ordinary hydrogen oxide (H2O) molecules. For instance, the heavy water used in CANDU reactors is 99.75% enriched by hydrogen atom-fraction—meaning that 99.75% of the hydrogen atoms are of the heavy type. For comparison, ordinary water (the "ordinary water" used for a deuterium standard) contains only about 156 deuterium atoms per million hydrogen atoms.
Cheeseburger in Hydrochloric Acid - Periodic Table of
Gastric acid is one of the main secretions of the stomach. It consists mainly of hydrochloric acid and acidifies the stomach content to a pH of 1 to 2.[31][32]
Chloride (Cl−) and hydrogen (H+) ions are secreted separately in the stomach fundus region at the top of the stomach by parietal cells of the gastric mucosa into a secretory network called canaliculi before it enters the stomach lumen.[33]
Gastric acid acts as a barrier against microorganisms to prevent infections and is important for the digestion of food. Its low pH denatures proteins and thereby makes them susceptible to degradation by digestive enzymes such as pepsin. The low pH also activates the enzyme precursor pepsinogen into the active enzyme pepsin by self-cleavage. After leaving the stomach, the hydrochloric acid of the chyme is neutralized in the duodenum by sodium bicarbonate.[31]
The stomach itself is protected from the strong acid by the secretion of a thick mucus layer, and by secretin induced buffering with sodium bicarbonate. Heartburn or peptic ulcers can develop when these mechanisms fail. Drugs of the antihistaminic and proton pump inhibitor classes can inhibit the production of acid in the stomach, and antacids are used to neutralize existing acid.[31][34]
Diamonds, Pearls and Atomic Bomb Stones - Periodic Table of Videos
In mineralogy, diamond (/ˈdaɪəmənd/ or /ˈdaɪmənd/; from the ancient Greek ἀδάμας – adámas "unbreakable") is a metastable allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at standard conditions. Diamond is renowned as a material with superlative physical qualities, most of which originate from the strong covalent bonding between its atoms. In particular, diamond has the highest hardness and thermal conductivity of any bulk material. Those properties determine the major industrial application of diamond in cutting and polishing tools and the scientific applications in diamond knives and diamond anvil cells.
Because of its extremely rigid lattice, it can be contaminated by very few types of impurities, such as boron and nitrogen. Small amounts of defects or impurities (about one per million of lattice atoms) color diamond blue (boron), yellow (nitrogen), brown (lattice defects), green (radiation exposure), purple, pink, orange or red. Diamond also has relatively high optical dispersion (ability to disperse light of different colors).
A pearl is a hard object produced within the soft tissue (specifically the mantle) of a living shelled mollusc. Just like the shell of a clam, a pearl is composed of calcium carbonate in minute crystalline form, which has been deposited in concentric layers. The ideal pearl is perfectly round and smooth, but many other shapes (baroque pearls) occur. The finest quality natural pearls have been highly valued as gemstones and objects of beauty for many centuries. Because of this, pearl has become a metaphor for something rare, fine, admirable and valuable.
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion (thermonuclear weapon). Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission ("atomic") bomb test released the same amount of energy as approximately 20,000 tons of TNT (see Trinity (nuclear test)). The first thermonuclear ("hydrogen") bomb test released the same amount of energy as approximately 10,000,000 tons of TNT.[1]
Chemistry in India - Periodic Table of Videos
In 1917, Raman resigned from his government service after he was appointed the first Palit Professor of Physics at the University of Calcutta. At the same time, he continued doing research at the Indian Association for the Cultivation of Science (IACS), Calcutta, where he became the Honorary Secretary. Raman used to refer to this period as the golden era of his career. Many students gathered around him at the IACS and the University of Calcutta.
Raman spectroscopy came to be based on this phenomenon, and Ernest Rutherford referred to it in his presidential address to the Royal Society in 1929. Raman was president of the 16th session of the Indian Science Congress in 1929. He was conferred a knighthood, and medals and honorary doctorates by various universities. Raman was confident of winning the Nobel Prize in Physics as well, but was disappointed when the Nobel Prize went to Owen Richardson in 1928 and to Louis de Broglie in 1929. He was so confident of winning the prize in 1930 that he booked tickets in July, even though the awards were to be announced in November, and would scan each day's newspaper for announcement of the prize, tossing it away if it did not carry the news.[11] He did eventually win the 1930 Nobel Prize in Physics "for his work on the scattering of light and for the discovery of the Raman effect".[12] He was the first Asian and first non-white to receive any Nobel Prize in the sciences. Before him Rabindranath Tagore (also Indian) had received the Nobel Prize for Literature in 1913.
Raman and Suri Bhagavantam discovered the quantum photon spin in 1932, which further confirmed the quantum nature of light.[13]
Raman had association with the Banaras Hindu University in Varanasi; he attended the foundation ceremony of BHU[14] and delivered lectures on "Mathematics" and "Some new paths in physics" during the lecture series organised at BHU from February 5 to 8, 1916.[15] He also held the position of permanent visiting professor at BHU.[16]
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