:: wikimiki.org ::

Explosive Limit

Explosive limit

The explosive limit of a gas or a vapour, is the limiting concentration (in air) that is needed for the gas to ignite and explode. There are two explosive limits for any gas or vapor, the lower explosive limit (LEL) and the upper explosive limit (UEL). At concentrations in air below the LEL there is not enough fuel to continue an explosion; at concentrations above the UEL the fuel has displaced so much air that there is not enough oxygen to begin a reaction. Concentrations of explosive gases are often given in terms of percent of lower explosive limit (%LEL). Controlling gas and vapor concentrations outside the explosive limits is a major consideration in occupational safety. Methods used to control the concentration of a potentially explosive gas or vapor include use of sweep gas, an inert gas such as nitrogen or argon to dilute the explosive gas before coming in contact with air. Use of scrubbers or adsorbtion resins to remove explosive gases before release are also common. Gases can also be maintained safely at concentrations above the UEL, although a breach in the storage container can lead to explosive conditions. The explosive limits of some gases and vapors are given below. Concentrations are given in percent by volume in air.

References

- David R. Lide, Editor-in-Chief; CRC Handbook of Chemistry and Physics, 72nd edition; CRC Press; Boca Raton, Florida; 1991; ISBN 0-8493-0565-9
- MSDS(Material Safety Data Sheet) from www.msdssearch.com and www.kosha.net (korea occupational safety & health agency). Category:Chemical properties

Gas

:For other meanings see gas (disambiguation). ---- A gas is one of the four main phases of matter (after solid and liquid, and followed by plasma), that subsequently appear as a solid material is subjected to increasingly higher temperatures. Thus, as energy in the form of heat is added, a solid (e.g. ice) will first melt to become a liquid (e.g. water), which will then boil or evaporate to become a gas (e.g. water vapor). In some circumstances, a solid (e.g. "dry ice") can directly turn into a gas: this is called sublimation. If the gas is further heated, its atoms or molecules can become (wholly or partially) ionized, turning the gas into a plasma.

Properties of a gas

#All collisions are perfectly elastic #The gas fills the entire container #The molecules have negligible volume In the gas phase, the atoms or molecules constituting the matter basically move independently, with no forces keeping them together or pushing them apart. Their only interactions are rare and random collisions. The particles move in random directions, at high speeds, whose range is dependent on the temperature and defined by the Maxwell-Boltzmann distribution. Therefore, the gas phase is a completely disordered state. Following the second law of thermodynamics, gas particles will immediately diffuse to homogeneously fill any shape or volume of space that is made available to them. The thermodynamic state of a gas is characterized by its volume, its temperature, which is determined by the average velocity or kinetic energy of the molecules, and its pressure, which is determined by the average velocity and density or number of molecules. These variables are related by the fundamental gas laws, which state that the pressure in an ideal gas is proportional to its temperature and number of molecules, but inversely proportional to its volume. Like liquids and plasmas, gases are fluids: they have the ability to flow and do not tend to return to their former configuration after deformation, although they do have viscosity. Unlike liquids, however, unconstrained gases do not occupy a fixed volume, but expand to fill whatever space they occupy. The kinetic energy per molecule in a gas is the second greatest of the states of matter (after plasma). Because of this high kinetic energy, gas atoms and molecules tend to bounce off of any containing surface and off one another, the more powerfully as the kinetic energy is increased. A common misconception is that the collisions of the molecules with each other is essential to explain gas pressure, but in fact their random velocities are sufficient to define that quantity. Mutual collisions are important only for establishing the Maxwell-Boltzmann distribution. Gas particles are normally well separated, as opposed to liquid particles, which are in contact. A material particle (say a dust mote) in a gas moves in Brownian Motion. Since it is at the limit of (or beyond) current technology to observe individual gas particles (atoms or molecules), only theoretical calculations give suggestions as to how they move, but their motion is different from Brownian Motion. The reason is that Brownian Motion involves a smooth drag due to the frictional force of many gas molecules, punctuated by violent collisions of an individual (or several) gas molecule(s) with the particle. The particle (generally consisting of millions or billions of atoms) thus moves in a jagged course, yet not so jagged as we would expect to find if we could examine an individual gas molecule.

Etymology

The word "gas" was apparently coined in the early 17th century by the Belgian chemist Jan Baptist van Helmont, as a re-spelling of his pronunciation of the Greek word chaos.

Concentration

:For the psychological concept, see attention. For the game, see Concentration (game), for the game show, see Concentration (game show). In chemistry, concentration is the measure of how much of a given substance there is mixed with another substance. This can apply to any sort of chemical mixture, but most frequently is used in relation to solutions, where it refers to the amount of solute dissolved in a solvent. To concentrate a solution, one must add more solute, or reduce the amount of solvent (for instance, by selective evaporation). By contrast, to dilute a solution, one must add more solvent, or reduce the amount of solute. There exists a concentration at which no further solute will dissolve in a solution. At this point, the solution is said to be saturated. If additional solute is added to a saturated solution, it will not dissolve. Instead, phase separation will occur, leading to either coexisting phases or a suspension. The point of saturation depends on many variables such as ambient temperature and the precise chemical nature of the solvent and solute. Concentration may be expressed both qualitatively ('informally') or quantitatively ('numerically').

Qualitative notation

Qualitatively, solutions of relatively low concentration are described using adjectives such as "dilute," or "weak," while solutions of relatively high concentration are described as "concentrated," or "strong." As a rule, the more concentrated a chromatic solution is, the more intensely coloured it is. chromatic

Quantitative notation

Quantitative notation of concentration is far more informative and useful from a scientific point of view. There are a number of different ways to quantitatively express concentration; the most common are listed below. Note: Many units of concentration require measurement of a substance's volume, which is variable depending on ambient temperature and pressure. Unless otherwise stated, all the following measurements are assumed to be at standard state temperature and pressure (that is, 25 degrees Celsius at 1 atmosphere or 101.325 kPa).

Mass percentage

Mass percentage denotes the mass of a substance in a mixture as a percentage of the mass of the entire mixture. For instance: if a bottle contains 40 grams of ethanol and 60 grams of water, then it contains 40% ethanol by mass. Commercial concentrated aqueous reagents such as acid and bases are often labeled in concentrations of weight percentage with the specific gravity also listed. In older texts and references this is sometimes referred to as weight-weight percentage (abbreviated as w/w).

Mass-volume percentage

Mass-volume percentage, (sometimes referred to as weight-volume percentage and often abbreviated as % m/v or % w/v) denotes the mass of a substance in a mixture as a percentage of the volume of the entire mixture. Mass-volume percentage is often used for solutions made from solid reagents. It is the mass of the solute in grams multiplied by one hundred divided by the volume of solution in milliliters.

Volume-volume percentage

Volume-volume percentage or % (v/v) describes the volume of the solute in mL per 100 mL of the resulting solution. This is most useful when a liquid - liquid solution is being prepared. For example, beer is about 5% ethanol by volume. This means every 100 mL beer contains 5 mL ethanol (ethyl alcohol).

Molarity

Molarity (M) denotes the number of moles of a given substance per litre of solution. For instance: 4.0 litres of liquid, containing 2.0 moles of dissolved particles, constitutes a solution of 0.5 M. Such a solution may be described as "0.5 molar." (Working with moles can be highly advantageous, as they enable measurement of the absolute number of particles in a solution, irrespective of their weight and volume. This is often more useful when performing stoichiometric calculations.). See molar solution for further information.

Molality

Molality (m) denotes the number of moles of a given substance per kilogram of solvent. For instance: 2.0 kilograms of solvent, containing 1.0 moles of dissolved particles, constitutes a molality of 0.5 mol/kg. Such a solution may be described as "0.5 molal." The advantage of molality is, it does not change with the temperature, as it deals with the mass of solvent rather than the volume of solution. Volume typically increases with increase in temperature resulting in decrease in molarity. Molality of a solution is always constant irrespective of the physical conditions like temperature and pressure.

Molinity

Molinity is a rarely-used term that denotes the number of moles of a given substance per kilogram of solution. For instance: imagine 2.0 kg of solvent, plus 1.0 mol of dissolved particles, weighs a total of 2.5 kg. The molinity of the solution is therefore 1 mol / 2.5 kg = 0.4 mol/kg. :Note: molarity and molinity are calculated using the volume of the entire solution, but molality is calculated using the mass of solvent only. :Warning: There may be confusion between above terms, which look and sound very similar; also, the abbreviations 'M' (denoting molarity) and 'm' (denoting molality) can be ambiguous. Special care should be exercised; if there is any risk of confusion, one should fully describe the measure being used.

Normality

Normality is a concept related to molarity, usually applied to acid-base solutions and reactions. For acid-base reactions, the equivalent is the mass of acid or base that can accept or donate exactly one mole of protons (H⁺ ions). Normality is also used for redox reactions. In this case the equivalent is the quantity of oxidizing or reducing agent that can accept or furnish one mole of electrons. Whereas molarity measures the number of particles per litre of solution, normality measures the number of equivalents per litre of solution. In practice, this simply means one multiplies the molarity of a solution by the valence of the ionic solute. A bit more complex for redox reactions. Note: The normality is always equal to, or greater than the molarity for acid-base reactions. However, for redox reactions the normality is typically equal to or less than the molarity.

Mole fraction

The mole fraction χ, chi (also called molar fraction) denotes the number of moles of solute as a proportion of the total number of moles in a solution. For instance: 1 mole of solute dissolved in 9 moles of solvent would have a mole fraction of 1/10 or 0.1.

Formal

The formal (F) is yet another measure of concentration similar to molarity. It is used rarely. It is calculated based on the formula weights of chemicals per litre of solution. The difference between formal and molar concentrations is that the formal concentration indicates moles of the original chemical formula in solution, without regard for the species that actually exist in solution. Molar concentration, on the other hand, is the concentration of species in solution. For example: if one dissolves sodium carbonate (Na₂CO₃) in a litre of water, the compound dissociates into the Na⁺ and CO₃^2- ions. Some of the CO₃^2- reacts with the water to form HCO₃^- and H₂CO₃. If the pH of the solution is low, there is practically no Na₂CO₃ left in the solution. So, although we have added 1 mol of Na₂CO₃ to the solution, it does not contain 1 M of that substance. (Rather, it contains a molarity based on the other constituents of the solution.) However, one can still say that the solution contains 1 F of Na₂CO₃.

"Parts-per" notation

The parts-per notation is used for extremely low concentrations. This is often used to denote the relative abundance of trace elements in the Earth's crust, trace elements in forensics or other analyses, or levels of pollutants in the environment.
- Parts per hundred (denoted by '%' and very rarely 'pph') - denotes one particle of a given substance for every 99 other particles. This is the common percent. 1 part in 10².
- Parts per thousand (denoted by '‰' [the per mil symbol], and occasionally 'ppt') denotes one particle of a given substance for every 999 other particles. This is roughly equivalent to one drop of ink in a cup of water, or one second per 17 minutes. 'Parts per thousand' is often used to record the salinity of seawater. 1 part in 10³.
- Parts per million ('ppm') denotes one particle of a given substance for every 999,999 other particles. This is roughly equivalent to one drop of ink in a 40 gallon drum of water, or one second per 280 hours. 1 part in 10⁶.
- Parts per billion ('ppb') denotes one particle of a given substance for every 999,999,999 other particles. This is roughly equivalent to one drop of ink in a canal lock full of water, or one second per 32 years. 1 part in 10⁹.
- Parts per trillion ('ppt') denotes one particle of a given substance for every 999,999,999,999 other particles. This is roughly equivalent to one drop of ink in an Olympic-sized swimming pool, or one second every 320 centuries. 1 part in 10¹².
- Parts per quadrillion ('ppq'?) denotes one particle of a given substance for every 999,999,999,999,999 other particles. This is roughly equivalent to a drop of ink in a medium-sized lake, or one second every 32,000 millennia. There are no known analytical techniques that can measure with this degree of accuracy; nevertheless, it is still used in some mathematical models of toxicology and epidemiology. 1 part in 10¹⁵. Warning: although 'ppt' is usually used to denote 'parts per trillion', it is also on occasion used to denote 'parts per thousand'. If there is any chance of ambiguity, one should describe the abbreviation in full. According to the U.S. National Institute of Standards and Technology (NIST) Guide for the Use of the International System of Units (SI), "the language-dependent terms part per million, part per billion, and part per trillion ... are not acceptable for use with the SI to express the values of quantities." [http://physics.nist.gov/Pubs/SP811/sec07.html#7.10.3] which lists examples of alternative expressions. Notes for clarity: :The indication given above is that parts per notation refers to numbers of particles (equivalent to moles), whereas in the last column of the chart below it is given by mass (grams per kilogram). Those using the notation need to state their usage to avoid confusion. :In atmospheric chemistry the parts per notation is commonly expressed with a v following, such as ppmv (or ppvm is some usages), to indicate parts per million by volume. In gases ppmv is equivalent to ppm by particles (Avogadro's law). This works fine for gases, but may have problems with cloud droplets and smoke or other atmospheric particulate matter.

Techniques used to determine concentration

- Spectrophotometry
- Chromatography
- Various titration methods

Table of concentration measures

Frequently used standards of concentration
Measurement	Notation	Generic formula	Typical units
Mass percentage	-	$\left ( \frac \right )$	%
Mass-volume percentage	-	$\left ( \frac \right )$	% though strictly %kg/L
Volume-volume percentage	-	$\left ( \frac \right )$	%
Molarity	M	$\left ( \frac \right )$	mol/L (or M)
Molinity	-	$\left ( \frac \right )$	mol/kg
Molality	m	$\left ( \frac \right )$	mol/kg (or m)
Molar fraction	χ (chi)	$\left ( \frac \right )$	(fraction)
Formal	F	$\left ( \frac \right )$	mol/L (or F)
Normality	N	$\left ( \frac \times valence\ of\ solute \right )$	N
Parts per hundred	% (or pph)	$\left ( \frac \right )$	da.g/kg
Parts per thousand	‰ (or ppt - )	$\left ( \frac \right )$	g/kg
Parts per million	ppm	$\left ( \frac \right )$	mg/kg
Parts per billion	ppb	$\left ( \frac \right )$	μg/kg
Parts per trillion	ppt -	$\left ( \frac \right )$	ng/kg
Parts per quadrillion	ppq	$\left ( \frac \right )$	pg/kg

- Although 'ppt' is usually used to denote 'parts per trillion', it is on occasion used for 'parts per thousand'. Sometimes 'ppt' is also used as an abbreviation for precipitate. Note (1) : The table above is described in terms of solvents and solutes; however the units given often also apply to other types of mixture. Note (2) : The use of billion, trillion, quadrillion above follows the short scale usage of these words. Category:Analytical chemistry ja:モル濃度

Oxygen

Oxygen is a chemical element in the periodic table. It has the symbol O and atomic number 8. The element is very common, found not only on Earth but throughout the universe, usually covalently bonded with other elements. Unbound oxygen (usually called molecular oxygen, O₂, a diatomic molecule) first appeared on Earth during the Paleoproterozoic era (between 2500 million years ago and 1600 million years ago) and as a product of the metabolic action of early anaerobes (archaea and bacteria). The presence of free oxygen drove most of the organisms then living to extinction. The atmospheric abundance of free oxygen in later geological epochs and up to the present has been largely driven by photosynthetic organisms, roughly three quarters by phytoplankton and algae in the oceans and one quarter from terrestrial plants.

Characteristics

At standard temperature and pressure, oxygen is mostly found as a gas consisting of a diatomic molecule with the chemical formula O₂. O₂ has two energetic forms:
- The low-energy predominant single-bonded diradical triplet oxygen. This native diradical quality of oxygen contributes to its destructive chemical nature. This form is stabilized by the degeneracy effect.
- The high-energy double-bonded molecule singlet oxygen. Oxygen is a major component of air, produced by plants during photosynthesis, and is necessary for aerobic respiration in animals. The word oxygen derives from two words in Greek, οξυς (oxys) (acid, sharp) and γεινομαι (geinomai) (engender). The name "oxygen" was chosen because, at the time it was discovered in the late 18th century, it was believed that all acids contained oxygen. The definition of acid has since been revised to not require oxygen in the molecular structure. Liquid O₂ and solid O₂ have a light blue color and both are highly paramagnetic. Liquid O₂ is usually obtained by the fractional distillation of liquid air. Liquid and solid O₃ (ozone) have a deeper color of blue. A recently discovered allotrope of oxygen, tetraoxygen (O₄), is a deep red solid that is created by pressurizing O₂ to the order of 20 GPa. Its properties are being studied for use in rocket fuels and similar applications, as it is a much more powerful oxidizer than either O₂ or O₃.

Applications

Liquid oxygen finds use as an oxidizer in rocket propulsion. Oxygen is essential to respiration, so oxygen supplementation has found use in medicine (as oxygen therapy). People who climb mountains or fly in airplanes sometimes have supplemental oxygen supplies (as air). Oxygen is used in welding (such as the oxyacetylene torch), and in the making of steel and methanol. Oxygen presents two absorption bands centered in the wavelengths 687 and 760 nanometers. Some scientists have proposed to use the measurement of the radiance coming from vegetation canopies in those oxygen bands to characterize plant health status from a satellite platform. This is because in those bands, it is possible to discriminate the vegetation's reflectance from the vegetation's fluorescence, which is much weaker. The measurement presents several technical difficulties due to the low signal to noise ratio and due to the vegetation's architecture, but it has been proposed as possibility to monitor the carbon cycle from satellite, thus in a global scale. Oxygen, as a mild euphoric, has a history of recreational use that extends into modern times. Oxygen bars can be seen at parties to this day. In the 19th century, oxygen was often mixed with nitrous oxide to promote an analgesic effect; indeed, such a mixture (Entonox) is commonly used in medicine today.

History

Oxygen was first discovered by Michał Sędziwój, Polish alchemist and philosopher in late 16th century. Sędziwój assumed the existence of oxygen by warming nitre (saltpeter). He thought of the gas given off as "the elixir of life". Oxygen was again discovered by the Swedish pharmacist Carl Wilhelm Scheele sometime before 1773, but the discovery was not published until after the independent discovery by Joseph Priestley on August 1, 1774, who called the gas dephlogisticated air (see phlogiston theory). Priestley published his discoveries in 1775 and Scheele in 1777; consequently Priestley is usually given the credit. It was named by Antoine Laurent Lavoisier after Priestley's publication in 1775.

Occurrence

Oxygen is the second most common component of the earth's atmosphere (20.947% by volume).

Compounds

Due to its electronegativity, oxygen forms chemical bonds with almost all other elements (which is the origin of the original definition of oxidation). The only elements to escape the possibility of oxidation are a few of the noble gases. The most famous of these oxides is dihydrogen monoxide, or water (H₂O). Other well known examples include compounds of carbon and oxygen, such as carbon dioxide (CO₂), alcohols (R-OH), aldehydes, (R-CHO), and carboxylic acids (R-COOH). Oxygenated radicals such as chlorates (ClO₃⁻), perchlorates (ClO₄⁻), chromates (CrO₄²⁻), dichromates (Cr₂O₇²⁻), permanganates (MnO₄⁻), and nitrates (NO₃⁻) are strong oxidizing agents in and of themselves. Many metals such as iron bond with oxygen atoms, iron (III) oxide (Fe₂O₃). Ozone (O₃) is formed by electrostatic discharge in the presence of molecular oxygen. A double oxygen molecule (O₂)₂ is known and is found as a minor component of liquid oxygen. Epoxides are ethers in which the oxygen atom is part of a ring of three atoms.

Isotopes

Oxygen has fifteen known isotopes with atomic masses ranging from 12 to 26. Three of them are stable and twelve are radioactive. The radioisotopes all have half lives of less than three minutes. The stable isotopes have mass numbers of 16, 17 and 18, of which oxygen-16 is the most common (over 99%).

Precautions

Oxygen can be toxic at elevated partial pressures (i.e. high relative concentrations). This is important in some forms of scuba diving, such as with a rebreather. Certain derivatives of oxygen, such as ozone (O₃), singlet oxygen, hydrogen peroxide, hydroxyl radicals and superoxide, are also highly toxic. The body has developed mechanisms to protect against these toxic species. For instance, the naturally-occurring glutathione can act as an antioxidant, as can bilirubin which is normally a breakdown product of hemoglobin. Highly concentrated sources of oxygen promote rapid combustion and therefore are fire and explosion hazards in the presence of fuels. This is true as well of compounds of oxygen such as chlorates, perchlorates, dichromates, etc. Compounds with a high oxidative potential can often cause chemical burns. The fire that killed the Apollo 1 crew on a test launchpad spread so rapidly because the pure oxygen atmosphere was at normal atmospheric pressure instead of the one third pressure that would be used during an actual launch. (See partial pressure.) Oxygen derivatives are prone to form free radicals, especially in metabolic processes. Because they can cause severe damage to cells and their DNA, they are thought to be related to cancer and aging.

References

- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://physics.nist.gov/cgi-bin/AtData/main_asd Nist atomic spectra database]
- [http://chartofthenuclides.com/default.html Nuclides and Isotopes Fourteenth Edition]: Chart of the Nuclides, General Electric Company, 1989

External links

- [http://www.priestleysociety.net Priestley Society, Dedicated to Joseph Priestley the man who discovered oxygen]
- [http://www.best-home-remedies.com/minerals/oxygen.htm Oxygen - Benefits, Deficiency Symptoms And Food Sources]
- [http://www.josephpriestley.info Joseph Priestley Information Website, about the man who discovered oxygen]
- [http://periodic.lanl.gov/elements/8.html Los Alamos National Laboratory – Oxygen]
- [http://www.webelements.com/webelements/elements/text/O/index.html WebElements.com – Oxygen]
- [http://education.jlab.org/itselemental/ele008.html It's Elemental – Oxygen]
- [http://members.tripod.com/tjaartdb0/html/oxygen_toxicity.html Oxygen Toxicity]
- [http://www.uigi.com/oxygen.html Oxygen (O2) Properties, Uses, Applications]
- [http://www.compchemwiki.org/index.php?title=Oxygen Computational Chemistry Wiki]
- [http://koti.mbnet.fi/antitz/dime/en Tests with liquid oxygen :-)] Category:Nonmetals Category:Chalcogens als:Sauerstoff ko:산소 ms:Oksigen ja:酸素 simple:Oxygen th:ออกซิเจน

Nitrogen

Nitrogen is the chemical element in the periodic table that has the symbol N and atomic number 7. Commonly a colorless, odorless, tasteless and mostly inert diatomic non-metal gas, nitrogen constitutes 78 percent of Earth's atmosphere and is a constituent of all living tissues. Nitrogen forms many important compounds such as amino acids, ammonia, nitric acid, and cyanides.

Notable characteristics

Nitrogen is a non-metal, with an electronegativity of 3.0. It has five electrons in its outer shell, so is trivalent in most compounds. Pure nitrogen is an unreactive colorless diatomic gas at room temperature, and comprises about 78.08% of the Earth's atmosphere. It condenses at 77 K at atmospheric pressure and freezes at 63 K. Liquid nitrogen is a common cryogen.

Applications

Nitrogen Compounds

Molecular nitrogen in the atmosphere is relatively non-reactive, but in nature it is slowly converted into biologically (and industrially) useful compounds by some living organisms, notably certain bacteria (see Biological role below). The ability to combine or fix nitrogen is a key feature of modern industrial chemistry, where nitrogen (along with natural gas) is converted into ammonia (via the Haber process). Ammonia, in turn, can be used directly (primarily as a fertilizer), or as a precursor of many other important materials including explosives, largely via the production of nitric acid by the Ostwald process. The salts of nitric acid include important compounds like potassium nitrate (or saltpeter, important historically for its use in gunpowder) and ammonium nitrate, an important fertilizer. Various other nitrated organic compounds, such as nitroglycerin and trinitrotoluene, are used as explosives. Nitric acid is used as an oxidizer in liquid fueled rockets. Hydrazine and hydrazine derivatives find use as rocket fuels.

Molecular nitrogen (gas and liquid)

Nitrogen gas is readily produced by allowing liquid nitrogen (see below) to warm up and evaporate. It has a wide variety of applications, including serving as a more inert replacement for air where oxidation is undesirable;
- to preserve the freshness of packaged or bulk foods (by delaying rancidity and other forms of oxidative damage)
- on top of liquid explosives for safety It is also used in:
- the production of electronic parts such as transistors, diodes, and integrated circuits
- the manufacture of stainless steel
- filling automotive tires due to its inertness and lack of moisture or oxidative qualities, as opposed to air. A further example of its versitility is its use (as a preferred alternative to carbon dioxide) to pressurize kegs of some beers, particularly thicker stouts and Scottish and English ales, due to the smaller bubbles it produces, which make the dispensed beer smoother and headier. A modern application of a pressure sensitive nitrogen capsule known commonly as a "widget" now allows nitrogen charged beers to be packaged in cans and bottles. A very popular example of this is Guinness Draught. Liquid nitrogen is produced industrially in large quantities by distillation from liquid air and is often referred to by the quasi-formula LN₂. It is a cryogenic (extremely cold) fluid which can cause instant frostbite on direct contact with living tissue. When appropriately insulated from ambient heat it serves as a compact and readily transported source of nitrogen gas without pressurization. Further, its ability to maintain an unearthly temperature as it evaporates (77 K, -196 °C or -320 °F) makes it extremely useful in a wide range of applications as an open-cycle refrigerant, including;
- the immersion freezing and transportation of food products
- the preservation of bodies, reproductive cells (sperm and egg), and biological samples and materials
- in the study of cryogenics
- for demonstrations in science education
- in dermatology for removing unsightly or potentially malignant skin lesions,e.g., warts, actinic keratosis, etc.

History

Nitrogen (Latin nitrum, Greek Nitron meaning "native soda", "genes", "forming") is formally considered to have been discovered by Daniel Rutherford in 1772, who called it noxious air or fixed air. That there was a fraction of air that did not support combustion was well known to the late 18th century chemist. Nitrogen was also studied at about the same time by Carl Wilhelm Scheele, Henry Cavendish, and Joseph Priestley, who referred to it as burnt air or phlogisticated air. Nitrogen gas was inert enough that Antoine Lavoisier referred to it as azote, which stands for without life; this term has become the French word for "nitrogen" and later spread out to many other languages. Compounds of nitrogen were known in the Middle Ages. The alchemists knew nitric acid as aqua fortis. The mixture of nitric and hydrochloric acids was known as aqua regia, celebrated for its ability to dissolve gold. The earliest industrial and agricultural applications of nitrogen compounds used it in the form of saltpeter (sodium- or potassium nitrate), notably in gunpowder, and much later, as fertilizer, and later still, as a chemical feedstock.

Occurrence

Nitrogen is the largest single component of the Earth's atmosphere (78.084% by volume, 75.5% by weight) and is acquired for industrial purposes by the fractional distillation of liquid air or by mechanical means of gaseous air (i.e. pressurised reverse osmosis membrane or PSA (Pressure Swing Adsorption). Compounds that contain this element have been observed in outer space. Nitrogen-14 is created as part of the fusion processes in stars. Nitrogen is a large component of animal waste (for example, guano), usually in the form of urea, uric acid, and compounds of these nitrogenous products. Molecular nitrogen has been known to occur in Titan's atmosphere for some time, and has now been detected in interstellar space by David Knauth and coworkers using the Far Ultraviolet Spectroscopic Explorer.

Compounds

The main hydride of nitrogen is ammonia (NH₃) although hydrazine (N₂H₄) is also well known. Ammonia is somewhat more basic than water, and in solution forms ammonium ions (NH₄⁺). Liquid ammonia is in fact slightly amphiprotic and forms ammonium and amide ions (NH₂^-); both amides and nitride (N^3-) salts are known, but decompose in water. Singly and doubly substituted compounds of ammonia are called amines. Larger chains, rings and structures of nitrogen hydrides are also known but virtually unstable. Other classes of nitrogen anions are azides (N₃^-), which are linear and isoelectronic to carbon dioxide. Another molecule of the same structure is dinitrogen monoxide (N₂O), or laughing gas. This is one of a variety of oxides, the most prominent of which are nitrogen monoxide (NO) and nitrogen dioxide (NO₂), which both contain an unpaired electron. The latter shows some tendency to dimerize and is an important component of smog. The more standard oxides, dinitrogen trioxide (N₂O₃) and dinitrogen pentoxide (N₂O₅), are actually fairly unstable and explosive. The corresponding acids are nitrous (HNO₂) and nitric acid (HNO₃), with the corresponding salts called nitrites and nitrates. Nitric acid is one of the few acids stronger than hydronium.

Biological role

Nitrogen is an essential part of amino and nucleic acids which makes nitrogen vital to all life. Legumes like the soybean plant, can recover nitrogen directly from the atmosphere because their roots have nodules harboring microbes that do the actual conversion to ammonia in a process known as nitrogen fixation. The legume subsequently converts ammonia to nitrogen oxides and amino acids to form proteins.

Isotopes

There are two stable isotopes: N-14 and N-15. By far the most common is N-14 (99.634%), which is produced in the CNO cycle in stars. The rest is N-15. Of the ten isotopes produced synthetically, one has a half life of nine minutes and the remaining isotopes have half lives on the order of seconds or less. Biologically-mediated reactions (e.g., assimilation, nitrification, and denitrification) strongly control nitrogen dynamics in the soil. These reactions almost always result in N-15 enrichment of the substrate and depletion of the product. Although precipitation often contains subequal quantities of ammonium and nitrate, because ammonium is preferentially retained by the canopy relative to atmospheric nitrate, most of the atmospheric nitrogen that reaches the soil surface is in the form of nitrate. Soil nitrate is preferentially assimilated by tree roots relative to soil ammonium.

Precautions

Nitrate fertilizer washoff is a major source of ground water and river pollution. Cyano (-CN) containing compounds form extremely poisonous salts and are deadly to many animals and all mammals.

References

- [http://periodic.lanl.gov/elements/7.html Los Alamos National Laboratory – Nitrogen]

External links

- [http://www.webelements.com/webelements/elements/text/N/index.html WebElements.com – Nitrogen]
- [http://education.jlab.org/itselemental/ele007.html It's Elemental – Nitrogen]
- [http://www.sunysccc.edu/academic/mst/ptable/n.html Schenectady County Community College – Nitrogen]
- [http://www.uigi.com/nitrogen.html Nitrogen N2 Properties, Uses, Applications]
- [http://box27.bluehost.com/~edsanvil/wiki/index.php?title=Nitrogen_gas Computational Chemistry Wiki] Category:Nonmetals Category:Pnictogens Category:Nitrogen metabolism ko:질소 ja:窒素 simple:Nitrogen th:ไนโตรเจน

Adsorbtion

In chemistry, adsorption of a substance or adsorbate is its concentration on a particular surface of adsorbent. The result is the formation of a liquid or gas film on the surface of a solid body. Consider a clean surface exposed to a gaseous atmosphere. In the bulk material, all the bonding requirements (be they ionic, covalent or metallic) of the constituent atoms of the material are filled. However, by definition, the surface represents a disruption of these bonds. It is then energetically favourable for these dangling bonds to react with whatever happens to be available. The exact nature of the bonding depends on the details of the species involved, but the adsorbed material is generally classed as being either physisorbed or chemisorbed. During the adsorption process, the quantity of an adsorbate which adheres to or is adsorbed in an adsorbent depends on several factors : adsorbent type, adsorbate type, adsorbent surface size, concentration of the adsorbate, and temperature. The simplest form of adsorption, physisorption, is due to weak forces of attraction, typically Van der Waals forces (also known as dispersion forces). Since these forces are ubiquitous, it follows that any clean exposed surface will rapidly accumulate a layer of physisorbed material. Chemisorption occurs when a chemical bond, defined in this case as an exchange of electrons, is formed. The degree of exchange, and how symmetric the exchange is, depends on the materials involved. There is often a close parallel with the situation encountered in coordination chemistry. Chemisorption is particularly important in heterogeneous catalysis, the most commonly encountered kind in industry, where a solid catalyst interacts with a gaseous feedstock, the reactant/s. The adsorption of reactant/s to the catalyst surface creates a chemical bond, altering the electron density around the reactant molecule and allowing it to undergo reactions that would not normally be available to it. The amount of material which accumulates depends on the dynamic equilibrium which is achieved between the rate at which material adsorbs to the surface and the rate at which it evaporates. The higher the rate of adsorption and the lower the rate of desorption, the greater the fraction of the available surface which will be covered by adsorbed material at equilibrium.

Boca Raton, Florida

Boca Raton is a city located in Palm Beach County, Florida and was incorporated in May of 1925. As of the 2000 census, the city had a total population of 74,764, the 2004 population recorded by the U.S. Census Bureau is 78,069.^{[http://www.census.gov/popest/cities/tables/SUB-EST2004-04-12.xls]}.

Geography

Boca Raton is located at (26.37, -80.10). Boca Raton is the southernmost city in Palm Beach County. It is located on the East coast of Florida between Delray Beach to the north and Deerfield Beach, in Broward County, to the south. It is the largest, most well known city between West Palm Beach and Fort Lauderdale. According to the United States Census Bureau, the city has a total area of 75.4 km² (29.1 mi²). 70.4 km² (27.2 mi²) of it is land and 5.0 km² (1.9 mi²) of it is water. The total area is 6.63% water.

Demographics

As of the census of 2000, there are 74,764 people, 31,848 households, and 20,000 families residing in the city. The population density is 1,061.7/km² (2,749.8/mi²). There are 37,547 housing units at an average density of 533.2/km² (1,381.0/mi²). The racial makeup of the city is 90.75% White, 3.76% African American, 0.16% Native American, 1.99% Asian, 0.04% Pacific Islander, 1.39% from other races, and 1.90% from two or more races. 8.51% of the population are Hispanic or Latino of any race. There are 31,848 households out of which 24.1% have children under the age of 18 living with them, 53.1% are married couples living together, 7.1% have a female householder with no husband present, and 37.2% are non-families. 29.5% of all households are made up of individuals and 11.6% have someone living alone who is 65 years of age or older. The average household size is 2.26 and the average family size is 2.81. In the city the population is spread out with 18.9% under the age of 18, 8.1% from 18 to 24, 26.4% from 25 to 44, 26.7% from 45 to 64, and 19.8% who are 65 years of age or older. The median age is 43 years. For every 100 females there are 95.1 males. For every 100 females age 18 and over, there are 92.8 males. The median income for a household in the city is $60,248, and the median income for a family is $77,861. Males have a median income of $52,287 versus $33,347 for females. The per capita income for the city is $45,628. 6.7% of the population and 4.1% of families are below the poverty line. Out of the total population, 6.0% of those under the age of 18 and 4.9% of those 65 and older are living below the poverty line. Boca Raton and its neighboring communities in south Palm Beach County have drawn a very large number of Modern Orthodox Jews who have established a network of synagogues and yeshivas. Many Jewish residents of this community tend to be involved with numerous Religious Zionist causes and express strong support for Israel.

History

The name "Boca Raton" predates the city, and was mistakenly given to the lake where the city stands by early nineteenth century mapmakers, even though there was no Boca Raton Inlet linking Boca Raton Lake with the ocean at the time. The original "Boca Ratones" was associated with an inlet in the Biscayne Bay area near Miami on eighteenth century maps. "Boca Ratones" literally translates from Spanish as "the mouse's mouth," but was an idiom meaning "Thieves' Inlet." The town's early history was as the site of Addison Mizner's Boca Raton Hotel, its most prominent building. The "pink hotel" today is visible from miles away as a towering building on the Intracoastal Waterway. The Pearl City neighborhood of Boca Raton was established to originally house the service personnel for the hotel. Japanese farmers of the Yamato Colony converted the land west of the city into pineapple plantations beginning in 1904. During World War II much of their land was confiscated and used as the site of a major training facility for B-29 bomber crews. Much of the airbase was later donated to become the grounds of Florida Atlantic University, many of whose parking lots are former runways of the airbase, while part of the airbase is now used as Boca Raton Airport. The Japanese heritage of the Yamato Colony survives in the name of Yamato Road (NW 51st Street) just north of the airport and at the Morikami Museum and Japanese Gardens northwest of the city. Boca Raton was the site of two now vanished amusement parks, Africa U.S.A. (1953-1961) and Ancient America (1953-1959). Africa U.S.A. was a wild animal park in which the tourists drove through the park and could view the animals outside their cars. It is now the Camino Gardens subdivision one mile (1.6 km) west of the Boca Raton Hotel. Ancient America was built surrounding a real Calusa Indian burial mound. Today, the mound is still visible within the Boca Marina & Yacht Club neighborhood on U.S. Highway 1, just north of Yamato Road. In the 1970s Boca Raton became home to a special subdivision of IBM which was responsible in 1981 for designing the first IBM PC. IBM relocated their manufacturing facilities for the PC to North Carolina and eventually closed down and sold their facility to Blue Lake which sold it to T-REX. A newer part of their facility (Building 051) was donated to the Palm Beach County School District which converted it into a school named Don Estridge High-Tech Middle School. It is named after Don Estridge, who's team designed the first Personal Computer. Boca Raton became famous for passing a city ordinance banning the further development of multi-family housing within the city limits and for special zoning that limits the size and types of commercial buildings and advertisement signs which may be erected within the city limits. There are no traditional car dealerships in Boca Raton because of these limits on roadside use, but a luxury car dealer did showcase a few cars inside a roadside building having glass walls. Corporations such as McDonald's had to redesign their classic "golden arches" restaurant to conform to Boca Raton's sign zoning restrictions. The effects can be seen in the city in which a number of buildings were constructed with classic Addison Mizner architecture and in the subdued roadside advertising. In 1991, a new downtown shopping center, Mizner Park, was built over the site of a defunct and vacant galleria mall. It has become a cultural center for the city. Featuring a landscaped central park between two cobblestone roads (collectively called Plaza Real) with stores only on the outside of the roads, Mizner Park resembles a Mediterranean suburb with a more contemporary look. It features many fine restaurants and is home to the Boca Raton Museum of Art. In 2002, a new amphitheater was built replacing a smaller one, providing a large-capacity outdoor venue. However, despite Mizner Park's success, crime and racism occured. In the mid 1990s, the Ku Klux Klan marched down Plaza Real; there were also several shootings, stick-ups, and a minor crime causing fountain damage from liquid soap. It was fixed many months after and was eased from Hurricane Frances washing it away. The fake bell tower was however severly damaged. These harsh crimes and natural problems didn't stop the downtown remodeling project. Six new high-rise buildings were built downtown. The historical Bank of America building built in the 1960s was renovated and Charles Schwab moved in on the east side. It is the only building above the height limit that is allowed to be and is a symbol of Boca Raton's skyline. In the early 21st century, Simon Malls bought out Town Center @ Boca Raton and rebuilt the mall with an extension. Originally, it was feeling doomed since Mervyn's closed its store as well as another in the city. Saks: Fifth Avenue then took and renovated the space and the old Saks was demolished and the lot was extended with a new anchor Nordstrom. The finished product was unveiled in late 2000 with over 25 new stores to shop in. It has now become a tourist attraction and one of the largest Simon malls in South Florida. Other projects such as the renovation and expansion of Boca Raton's YMCA facility will probably expand the city limits.

Education

It was in Boca Raton where the Episcopal School Foundation chartered the prestigious preparatory school, Saint Andrew's School in 1961. The Rev. Hunter Wyatt-Brown, Jr. (Headmaster from 1962-63) and Eugene Curtis, Jr. (Headmaster from 1964-71) led the effort to secure the land and funds necessary to build the school. Many in the community came forward to support the project, most notably Lucy and Alexander Henderson, who gave the majority of the funds needed to start the school. Pine Crest School, based in Ft. Lauderdale, has a campus in Boca Raton. Lynn University (originally founded as Marymount College, then re-named The College of Boca Raton in 1974, and finally Lynn University in 1991) is a four year co-educational institution re-named to honor the Lynn (Eugene & Christine) family who continue to be generous benefactors of the university. Florida Atlantic University, founded in 1961, held its first classes in Boca Raton in 1964. FAU is a member of the State University System of Florida. Palm Beach Community College has had a Boca Raton campus, adjacent to Florida Atlantic University, since 1983.

Residents

Many residents of Boca Raton are well known around the world including Chris Evert (tennis player), Andy Mill (skier), and Daniel Keyes (writer).

Controversies & Crime

Boca Raton was the site of the first anthrax attack in the United States when two employees at the American Media building. Robert "Bob" Stevens, photo editor of the Sun, a supermarket tabloid published by American Media, died of inhalation anthrax while Ernesto Blanco, a 73-year old mail room employee, recovered. American Media relocated their offices. The American Media building was sealed until the summer of 2004, when it became the last building in the United States to be decontaminated of anthrax spores using chlorine dioxide gas. See Timeline of the 2001 anthrax attacks in Florida. American Media has moved their HQ to New York City. According to MessageLabs, (an email security vendor), Boca Raton is the "spam capital of the world", being the source of a surprisingly high fraction of all spam generated worldwide. According to the Miami Herald, the town has a long history of involvement in confidence tricks. Richard C. Breeden, former U.S. Securities and Exchange Commission chairman, once called the town "the only coastal town in Florida where there are more sharks on land than in the water." In the keynote address to a computer security conference on 8 June, 2004, Bruce Sterling described the town as the "Capone-Chicago of cyber fraud." According to a number of US Federal indictments, as of June, 2004, the Gambino family continues to operate in Boca Raton. On 22 July 2004, Boca Raton resident Scott Levine was charged with the largest computer crime indictment in United States history. Federal prosecutors allege that Levine unlawfully accessed databases of consumer data aggregator [http://www.acxiom.com/ Acxiom] to steal detailed personal information about millions of persons. Several on-line sources claim that Levine is an associate of Eddy Marin, a pornographer and convicted cocaine dealer who runs one of the largest Boca Raton spam outfits. The indictment against Levine also includes money laundering charges. [http://www.cnn.com/2004/LAW/07/21/cyber.theft/] See history for more.

Transportation

Air: The Boca Raton Airport is a general aviation airport located immediately adjacent to Florida Atlantic University and Interstate-95. It has a control tower which is manned from 0700 to 2300. The Boca Raton Airport is publicly-owned and governed by a seven member Authority appointed by the City of Boca Raton and the Palm Beach County Commission. Palm Beach International Airport (PBI) is located to the north in West Palm Beach while Fort Lauderdale-Hollywood International Airport (FLL) is located to the south in Fort Lauderdale. Highway: I-95 bisects the city from north to south with four interchanges serving Boca Raton. The Florida Turnpike is immediately west of the city with one interchange at Glades Road. Rail: The Tri-Rail commuter rail system serves the city with its Boca Raton Station located on the south side of Yamato Road just west of I-95. CSX Transportation and the Florida East Coast Railway also serve the city.

Weather

On Monday, 24 October 2005, Hurricane Wilma struck Boca Raton with winds in excess of 100 mph. While Wilma was still over the Caribbean, it achieved the lowest central pressure of any Atlantic hurricane at 882 millibars, surpassing Hurricane Gilbert's low of 888 mb in 1988, thus making Wilma the most intense Atlantic hurricane on record. Wilma produced well over 60 inches of rainfall as it moved across the Yucatan Peninsula, then turned northeastward and made it's Florida landfall south of Naples as a Category 3 storm.

External links

- [http://www.ci.boca-raton.fl.us/ City of Boca Raton]
- [http://www.ci.boca-raton.fl.us/econ/history.cfm History of Boca Raton]
- [http://www.bocaratonchamber.com/ Greater Boca Raton Chamber of Commerce]
- [http://www.bocamuseum.org/ Boca Raton Museum of Art]
- [http://www.messagelabs.com/ MessageLabs website]
- [http://www.africa-usa.com/history.htm Africa U.S.A.]
- [http://www.lostparks.com/ancientamerica.html Ancient America]
- [http://www.centre4artsboca.com/events.asp Centre for the Arts]
- [http://www.miznerpark.org/directions.asp Mizner Park directions] Category:Cities in Florida Category:Palm Beach County, Florida Category:Orthodox Jewish communities

1991

1991 (MCMXCI) is a common year starting on Tuesday of the Gregorian calendar.

Events

January

- January 2 - Sharon Pratt Dixon is sworn in as mayor of Washington, DC becoming the first black woman to lead a city of that size and importance.
- January 4 - The United Nations Security Council votes unanimously to condemn Israel's treatment of Palestinians.
- January 10 - SA State Govt forced to bail out State Bank.
- January 11 - The Soviets storm Vilnius to stop Lithuanian independence.
- January 12 - Gulf War: The U.S. Congress passes a resolution authorizing the use of military force to liberate Kuwait.
- January 13 - The Soviet Union troops assault the Vilnius TV tower in Lithuania and kill 14 unarmed civilians, many more are injured.
- January 13 - Soccer stampede and fight at Johannesburg, South Africa - 42 dead.
- January 14 - Three PLO guerilla chiefs assassinated in Tunis.
- January 16 - US serial killer Aileen Wuornos confesses to the murders of six men.
- January 17 - Operation Desert Storm begins.
- January 17 - Gulf War: The air strikes against Iraq begin.
- January 17 - Gulf War: Iraq fires 8 Scud missiles into Israel.
- January 17 - Harald V becomes King of Norway on the death of his father, Olav V.
- January 18 - Eastern Airlines shuts down after 62 years citing financial problems.
- January 26 - The Somalian president Siad Barre flees his compound in Mogadishu.
- January 29 - Siad Barre is succeeded by Ali Mahdi Muhammad.

February

February.]]
- February 4 - The Baseball Hall of Fame votes to ban Pete Rose.
- February 5 - A Michigan court bars Dr Jack Kevorkian from assisting in suicides.
- February 7 - Haiti's first democratically-elected president, Jean-Bertrand Aristide, is sworn in.
- February 7 - The IRA launches a mortar attack on 10 Downing Street during a cabinet meeting.
- February 9 - Voters in Lithuania vote for independence.
- February 11 - UNPO, the Unrepresented Nations & Peoples Organization, forms in the Hague, Netherlands.
- February 13 - Gulf War: Two laser-guided "smart bombs" destroy an underground bunker in Baghdad killing hundreds of Iraqis. Iraqi officials claim that the bunker was a bomb shelter but United States military intelligence identified it as a military facility.
- February 15 - The Visegrad Agreement, establishing cooperation to move toward free-market systems, is signed by the leaders of Czechoslovakia, Hungary and Poland.
- February 16 - Gulf War: American and British war planes bomb the suburbs of Baghdad, injuring at least 11 civilians and killing three others.
- February 22 - Gulf War: Iraq accepts a Russian proposed cease fire agreement. The US rejects the agreement, but said that retreating Iraqi forces would not be attacked if they left Kuwait within 24 hours.
- February 23 - Gulf War: Ground troops cross the Saudi Arabian border and enter Kuwait, thus starting the ground phase of the war.
- February 23 - Thailand: General Sunthorn Kongsompong leads a bloodless coup d'état, deposing Prime Minister Chatichai Choonhavan.
- February 25 - Gulf War: An Iraqi Scud missile hits an American military barracks in Dhahran, Saudi Arabia killing 28 US Marines.
- February 26 - Gulf War: On Baghdad radio, Iraqi leader Saddam Hussein announces the withdrawal of Iraqi troops from Kuwait. Iraqi soldiers set fire to Kuwaiti oil fields as they retreat.
- February 27 - Gulf War: Kuwait is liberated, and a ceasefire is declared, after 100 hours of ground fighting. Iraq accepts the terms of the ceasefire, which call for the country to disarm.

March

- March-April - Iraqi forces suppress rebellions in the southern and northern parts of the country, creating a humanitarian disaster on the borders of Turkey and Iran
- March 1 - Ballistic Missile Submarine USS-Lafayette (now ex-Lafayette) starts to be deactivated
- March 1 - Ethan-Allen-class submarine USS-Sam Houston (now ex-Sam Houston SSBN-609) starts to be deactivated
- March 1 - Clayton Keith Yeutter finishes as the United States Secretary of Agriculture, under the George H. W. Bush administration
- March 3 - An amateur video captures the beating of Rodney King by Los Angeles police officers.
- March 3 - Latvia and Estonia vote to become independent of the Soviet Union
- March 4 - Vermont celebrates its bicentennial statehood.
- March 4 - Most primitive form of World Wide Web is put online.
- March 9 - Massive demonstrations are held against Slobodan Milošević in Belgrade. Two people are killed and tanks are in the streets
- March 10 - Gulf War: Operation Phase Echo - 540,000 American troops begin to leave the Persian Gulf
- March 11 - A curfew is imposed on black townships in South Africa after fighting between rival political gangs killed 49.
- March 13 - The United States Department of Justice announces that Exxon has agreed to pay $1 billion for the clean-up of the Exxon Valdez oil spill in Alaska.
- March 14 - After 16 years in prison for allegedly bombing a pub in an Irish Republican Army attack, the "Birmingham Six" are freed when a court determines that the police fabricated evidence
- March 15 - Four Los Angeles, California police officers are indicted for the videotaped March 3, 1991 beating of motorist Rodney King during an arrest.
- March 15 - Germany formally regains complete independence after the four post-World War II occupying powers (France, the United Kingdom, the United States and the Soviet Union) relinquish all remaining rights.
- March 31 - The Warsaw Pact is officially dissolved.
- March 31 - Albania has the first multi-party elections

April

- April 1 - The New York Times, the Washington Post, and the Los Angeles Times report that [http://us.imdb.com/name/nm0910366/ Selene Walters] had verified her claim that then SAG President Ronald Reagan raped her in her home in 1952
- April 3 - Iraq disarmament crisis: The U.N. Security Council passes the Cease Fire Agreement, Resolution 687. The resolution called for the destruction or removal of all of Iraq's chemical and biological weapons, all stocks of agents and components, and all research, development, support and manufacturing facilities for ballistic missiles with a range greater than 150km and production facilities; and for an end to its support for international terrorism. Iraq accepts the terms of the resolution on April 6
- April 4 - Senator John Heinz of Pennsylvania and six others are killed when a helicopter collided with their plane over Merion, Pennsylvania
- April 9 - Supreme Council of the Republic of Georgia declared the restoration of independence of Georgia
- April 10 - A rare tropical storm develops in the Southern Hemisphere off the coast of Angola; the first of its kind to be documented by Satelites.
- April 14 - In the Netherlands, thieves steal 20 paintings worth $500 million from the Van Gogh Museum in Amsterdam. Less than an hour later they are found in an abandoned car near the museum
- April 17 - After approaching 3,000 in July 1990, the Dow Jones Industrial Average closes above 3,000 for the first time ever, closing at 3,004.46.
- April 17 - First Performance of Nirvana's "Smells Like Teen Spirit" at the OK Hotel in Seattle, Washington the song that marked the beggining of a new movement in music called Grunge. It managed to turn a crowd calmly seated at tables into a moshpit.
- April 18 - Iraq disarmament crisis: Iraq declares some of its chemical weapons and materials to the UN, as required by Resolution 687, and claims that it does not have biological weapons program.
- April 26 - Tornadoes break out in the central United States. The most notable tornado of the day was the one that hit in Andover, Kansas. The outbreak of nearly seventy tornadoes killed 17 people in Kansas, Oklahoma and Texas. The tornado that hit Andover was the only F5 of the year. (see The Andover, Kansas Tornado)
- April 29 - A tropical cyclone hits Bangladesh killing an estimated 138,000 people.

May

- May 5 - The shooting of a Salvadoran man by police in the Mount Pleasant neighborhood of Washington D.C. ignites the Cinco de Mayo Riots, which bring the city to a standstill for 3 days.
- May 15 - Edith Cresson becomes France's first female premier
- May 16 - HM Queen Elizabeth II gives a speech to the US Congress.
- May 19 - Willy T. Ribbs becomes the first African-American driver to qualify for the Indianapolis 500
- May 21 - In Sri Perumbudur near Madras, former Indian prime minister Rajiv Gandhi is assassinated by a terrorist bomb hidden in a bouquet of flowers
- May 26 - In Thailand, a Lauda Air Boeing 767 crashes near Bangkok killing all 223 people on-board
- May 28 - The capital city of Addis Ababa falls to the Ethiopian People's Revolutionary Democratic Front, ending both the Derg regime in Ethiopia and the Ethiopian Civil War.

June

- June 6 - George and Barbara Loeb, members of the Church of the Creator, are arrested and charged with murder
- June 12 - Boris Yeltsin is elected president of Russia, the largest and most populous of the fifteen Soviet republics.
- June 13 - A spectator is killed by lightning at the U.S. Open [http://www.crh.noaa.gov/mkx/slide-show/tstm/slide114.html]
- June 15 - Pinatubo climactic eruption, one of the most destructive volcanic event of the century shaked the Phillipines
- June 17 - Apartheid: The South African Parliament repeals the Population Registration Act, which had required racial classification of all South Africans at birth
- June 17 - Exhemation of US President Zachary Taylor to discover whether or not his death was caused by arsenic poisoning, instead of acute gastrointestinal illness. No trace of arsenic is found.
- June 23 - Sonic the Hedgehog was created and released for the Sega Genesis
- June 23-June 28 - Iraq disarmament crisis: U.N. inspection teams attempt to intercept Iraqi vehicles carrying nuclear related equipment. Iraqi soldiers fire warning shots in the air to prevent inspectors from approaching the vehicles
- June 25 - Croatia and Slovenia declare their independence from Yugoslavia

July

- July 1 - The Warsaw Pact is officially dissolved.
- July 7 - The Brioni Agreement ends the ten day war in Slovenia
- July 9 - International Human Rights Federation cites human rights violations committed by police and military personnel during Oka crisis in Quebec.
- July 10 - Boris Yeltsin begins his 5-year term as the first elected president of Russia
- July 11 - Total Solar Eclipse.(Hawaii, Mexico, Central America, Colombia and Brazil).
- July 19 - Mike Tyson rapes Desiree Washington.
- July 22 - Serial killer Jeffrey Dahmer is arrested after the remains of 11 men and boys are found in his Milwaukee, Wisconsin apartment.

August

August is torn down in Moscow, signalling the Collapse of the Soviet Union.]]
- August 6 - Tim Berners-Lee releases files describing his idea for the "World Wide Web."
- August 7 - Assassination of Shapora Baktiari, former prime minister of Iran
- August 8 - Collapse of Warsaw radio mast, the tallest construction ever built
- August 17 - Strathfield Massacre (Sydney, Australia) - taxi driver Wade Frankum shoots seven people and injuring 6 others before turning the gun on himself.
- August 18 - Collapse of the Soviet Union: Soviet President Mikhail Gorbachev is put under house arrest while vacationing in the Crimea. The putsch is led by eight high-ranking hard-liners, and will collapse in less than 72 hours.
- August 20 - Collapse of the Soviet Union: Estonia declares its independence from the Soviet Union and more than 100,000 people rally outside the Soviet Union's parliament building protesting the coup that deposed President Mikhail Gorbachev
- August 21 - Collapse of the Soviet Union: Latvia declares its independence from the Soviet Union
- August 24 - Ukraine declares independence from Soviet Union
- August 25 - Student Linus Torvalds post a messages to Usenet newsgroup comp.os.minix about the new operating system kernel he has been developing.
- August 29 - Maronite general Michel Aoun leaves Lebanon via a French ship into exile
- August 31 - Kyrgyzstan declares independence from the Soviet Union

September

- September 2 - The United States recognizes the independence of the Baltic states: Estonia, Latvia and Lithuania.
- September 3 - In Hamlet, North Carolina, a grease fire breaks out at the Imperial Foods chicken processing plant, killing 25 people.
- September 5 - Fall of Communism in the USSR.
- September 5-September 7 - At the 35th Annual Tailhook Symposium, 83 women and 7 men are assaulted.
- September 6 - The Soviet Union recognizes the independence of the Baltic States.
- September 6 - The name "Saint Petersburg" is restored to Russia's second-largest city, which had been renamed "Leningrad" in 1924.
- September 8 - Republic of Macedonia becomes independent.
- September 15 - The C-17 Globemaster III flys for the first time. The C-17 is regarded by many in the industry as the best, safest and most capable aircraft in the history of aviation.
- September 16 - Guns N' Roses Use Your Illusion album was released.
- September 21 - Armenia declares independence from the Soviet Union
- September 21-September 30 - Iraq disarmament crisis: IAEA inspectors discover files on Iraq's hidden nuclear weapons program. Iraqi officials confiscate documents from UN weapons inspectors, and refuse to allow them to leave the site without turning over other documents. A four-day standoff ensues. Iraq permits the team to leave with the documents after a statement from the UN Security Council threatens enforcement actions.
- September 22 - The Dead Sea Scrolls are made available to the public for the first time, by the Huntington Library.
- September 24 - The release of Nirvanas Nevermind signified the start of the Grunge era that would dominate the music scene up to the mid-90's.
- September 30 - Haitian President Jean-Bertrand Aristide is removed from power.

October

- October 2 - Arkansas Governor William J. Clinton announces he will seek the 1992 Democratic Party nomination for President of the United States.
- October 8 - The Croatian Parliament cuts all remaining ties with Yugoslavia
- October 11 - KGB is replaced by the SVR
- October 11 - Iraq disarmament crisis: The U.N. Security Council passes Resolution 715, which demands that Iraq "accept unconditionally the inspectors and all other personnel designated by the Special Commission". Iraq rejects the resolution, calling it "unlawful"
- October 12 - Askar Akayev, previously chosen President of Kyrgyzstan by republic's Supreme Soviet, is confirmed president in an uncontested poll
- October 14 - Bulgarians celebrate the end of the rule of the communist party
- October 15 - Following a bitter confirmation hearing that involved allegations of sexual misconduct, the United States Senate votes 52 to 48 to confirm Judge Clarence Thomas to the Supreme Court of the United States
- October 16 - George Hennard guns down 24 people in Texas
- October 19 - 7.0 Richter Scale earthquake in Northern Italy - 2000 dead
- October 20 - Oakland Hills firestorm kills 25 and destroys 3469 homes and apartments
- October 27 - The first free parliamentary elections in Poland
- October 29 - The American Galileo spacecraft makes its closest approach to 951 Gaspra, becoming the first probe to visit an asteroid
- Winter - Centennial of Basketball

November

- November 4 - Ronald Reagan opened his presidential library in Simi Valley.
- November 5 - Body of publishing tycoon Robert Maxwell is found floating in the sea - he had fallen off his yacht
- November 7 - Los Angeles Lakers point guard Magic Johnson announces that he has HIV, effectively ending his career in the NBA.
- November 7 - The last oil well was put out of fire in Kuwait.
- November 14 - American and British authorities announce indictments against two Libyan intelligence officials in connection with the downing of the Pan Am Flight 103
- November 14 - Cambodian Prince Norodom Sihanouk returns to Phnom Penh after 13 years of exile
- November 18 - Shiite Muslim kidnappers in Lebanon set Anglican Church envoys Terry Waite and Thomas Sutherland free
- November 18 - Serb troops take Vukovar after siege of 87 days
- November 23 - Freddie Mercury, lead singer of the band Queen, issues a public statement confirming that he is stricken with AIDS. He would die of complications the next day.
- November 24 - Freddie Mercury dies of AIDS in his home in London, of AIDS-Related Chronic problems.
- November 27 - The United Nations Security Council unanimously adopts UN Security Council Resolution 721, opening the way to the establishment of peacekeeping operations in Yugoslavia.
- November 29 - Federal Yugoslavian Army begins to withdraw from Zagreb

December

- December 1 - Cold War: Ukrainian voters overwhelmingly approve a referendum for independence from the Soviet Union
-

Explosive limit

References

Gas

Properties of a gas

Etymology

See also

Concentration

Qualitative notation

Quantitative notation

Mass percentage

Mass-volume percentage

Volume-volume percentage

Molarity

Molality

Molinity

Normality

Mole fraction

Formal

"Parts-per" notation

Techniques used to determine concentration

Table of concentration measures

Oxygen

Characteristics

Applications

History

Occurrence

Compounds

Isotopes

Precautions

See also

References

External links

Nitrogen

Notable characteristics

Applications

Nitrogen Compounds

Molecular nitrogen (gas and liquid)

History

Occurrence

Compounds

Biological role

Isotopes

Precautions

See also

References

External links

Adsorbtion

See also

Boca Raton, Florida

Geography

Demographics

History

Education

Residents

Controversies & Crime

Transportation

Weather

External links

1991

Events