Ammonia and hydrazine

Ammonia (consisting of one part nitrogen and three parts hydrogen) is one of the most im-

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Major groups of elements: Nitrogen 47

portant compounds of nitrogen. It has a sharp, pungent odor and is an extremely soluble gas. Although found in nature, it can be easily and cheaply produced commercially. Hydrogen (usually from natural gas) and nitrogen (from the air) are combined under high pressure and temperature using a catalyst, a substance that speeds up chemical reactions.

Ammonia is produced in large quantities for conversion to fertilizers. Because of their high nitrogen content, ammonia fertilizers help increase crop production and quality. It is now possible to apply the ammonia gas di­rectly to some farming areas. Large tanks con­taining the compressed gas inject it into the fields.

Ammonia is also used in the production of explosives, such as TNT and nitroglycerin. In the textile industry, ammonia finds use in the making of synthetic fibers such as nylon and some types of rayon. It is also used in dyeing and scouring wool, cotton, and other natural fibers.

Because ammonia absorbs a large amount of heat when going from a liquid back to a gas, it is widely used in refrigeration equip­ment. Ammonia is further used in manufactur­ing cleaning fluids, various chemicals, plastics, vitamins, and drugs.

Hydrazine is a colorless, unstable, and cor­rosive liquid, made up of two parts nitrogen and four parts hydrogen. It is an important chemical compound that has many agricul­tural and industrial uses. It is a major ingredi­ent in jet and rocket fuels. It is used to make agricultural and textile chemicals, photo­graphic developing fluids, and explosives. Hy­drazine is used as a raw material in the pro­duction of pesticides, herbicides, and pharmaceuticals. It is also used in the manu­facture of foam rubber and certain plastics.

Oxides of nitrogen

Eight oxides of nitrogen are known. These are compounds containing nitrogen and oxygen in varying proportions. Nitrous oxide is a col­orless, unreactive gas sometimes known as laughing gas. It is used as a mild anesthetic, usually in combination with more powerful an­esthetics during major surgery. Nitric oxide and nitrogen dioxide are both used in the pro­duction of nitric acid. Nitric acid is used in the production of fertilizers, drugs, and explo­sives. The other oxides of nitrogen are unsta­ble and little studied, being of practically no use.

Dynamite(shown in use above) is a mixture of nitro­glycerin (glyceryl trinitrate) and an inert substance such as kieselguhr or wood pulp. The inert substance is added to make the nitro­glycerin safer to handle.

The nitrogen content of the soilis increased by spraying with nitrate fertiliz­ers (below). Nitrogen is also added to the soil by the ac­tivity of nitrifying bacteria in the root nodules of certain plants (below left), such as clover, beans, and peas.

Fact entries

Nitrogen was first recog­nized by the French chemist Antoine Lavoisier (1734-1794). He named it azote, meaning "without life," be­cause of its inability to sup­port life. However, the ele­ment's discovery in 1772 is credited to the Scottish phy­sician Daniel Rutherford

(1749-1819). Its present name, coined in 1790, means "niter forming," be­cause of nitrogen's pres­ence in niter (potassium ni­trate). At. no. 7; at. mass 14.0067; m.p. -209.9° C; b.p. -195.8°C.

The Haber-Bosch proc­ess,developed in the early twentieth century, is still an important method of mak­ing ammonia. Nitric acid and, in turn, explosives and fertilizers, are manufactured from ammonia. The key re­action is the combination of one molecule of nitrogen

(from air) and three mole­cules of hydrogen (now ob­tained from natural gas). The combination gives two mol­ecules of ammonia. Signifi­cant amounts of ammonia can be obtained only by using high pressures (be­tween 200 and 250 atmos­pheres), high temperatures

(about 500° C), and a catalyst to help speed the process.

The elements phospho­rus to bismuthcomplete Croup 5A of the periodic table, which is headed by nitrogen. They exhibit in­creasing metallic properties going down the group.

Powdered phosphate rockraises a cloud of dust that engulfs the handling machinery at a quarry in Jor­dan. Phosphate minerals— usually forms of calcium phosphate—are the major source of phosphorus and its compounds, particularly superphosphate for use as a fertilizer.

Phosphorus (P), arsenic (As), antimony (Sb), and bismuth (Bi) form a group of four elements in Group 5A of the periodic table. Nitrogen, which heads the group, is discussed in the previous article. Phosphorus is a highly reac­tive nonmetal, arsenic and antimony are poi­sonous metalloids, and bismuth is a true metal.

In some respects, phosphorus is similar to nitrogen. Both have typical nonmetallic charac­teristics. Both are essential to plant and animal tissue. But in other ways, phosphorus is very different from nitrogen. It is a solid at normal temperatures and occurs in various physical forms, or allotropes, with a variety of colors and chemical properties. One form of phos­phorus is also very poisonous, as are many of its compounds, particularly its organic com­pounds.

The other elements in the group are unlike nitrogen, but similar to phosphorus. Arsenic and antimony exist as different allotropes, and certain of their compounds are poisonous. From arsenic to bismuth, the elements look more and more like metals, and some of their chemical characteristics confirm this. Because of the arrangement of the outer electrons in their atoms, each of these elements can form up to five chemical bonds with other elements or groups of elements.

Phosphorus

Phosphorus occurs in both inorganic and or­ganic forms. The minerals phosphorite and ap­atite are found as deposits around the world. These phosphate rocks are found especially in Florida, and in Morocco and the Soviet Union. The element is also present in the droppings of sea birds (called guano), found in large quantities on the coast of Peru and some Pa­cific islands.

The bones and teeth of animals, including humans, contain phosphorus. In fact, every liv-

ing cell in plants and animals contains phos­phorus in some form or other—particularly the cells of the brain, muscles, and nervous sys- | tern.

Most phosphorus used industrially and ag­riculturally has to be produced commercially. There are three main allotropic (physical) forms of phosphorus—white, red, and black-each with very different chemical characteris­tics.

White phosphorus is a soft, waxlike solid. When exposed to air, it emits a faint green light that is visible in the dark. This glow-sometimes called phosphorescence—gives phosphorus its name, from the Greek word meaning light-bearer. In an abundant supply of air, white phosphorus burns easily, giving off a very poisonous vapor. For this reason, it is kept under water, with which it does not react. Because it burns so easily in the air, white phosphorus was once used to make matches. This was before it was known to be poisonous. Many workers in the match indus­try suffered from a dreaded tooth and bone disease known as "phossy jaw."

Red phosphorus is a much more stable form of the element. It is used today in the manufacture of matches, either on its own or in combination with sulfur. It is formed by heating white phosphorus for several hours at 750° F. (250° C) in the absence of air. Red phos­phorus ignites in air only on strong heating.

Another form of the element—black phosphorus—is made after heating white phosphorus at 430-700° F. (220-370° C) for 8 days with mercury as a catalyst. A catalyst is a substance that speeds up a chemical reaction. Black phosphorus can also be made by heat­ing phosphorus under very high pressure for a shorter time.

Phosphorus, in a form called phosphate, is essential for plant growth. Plants absorb phos­phorus from the soil. As the plants are cropped, the phosphorus is removed. Unlike nitrogen, it is not replaced by a natural cycle, and phosphorus-containing fertilizers need to be continuously added to the soil. These are prepared from natural sources of phosphorus-bearing minerals or from guano.

Phosphorus is also important in the produc­tion of poultry and animal feeds, steel, china, and baking powder. A type of red phosphorus is used in making pesticides and smoke bombs, as well as safety matches. Phosphoric acid is a basic chemical compound of phos­phorus. It is used in various drugs, soft drinks, flavoring syrups, and water softeners.

Date: 2015-12-11; view: 1260