Reactions with elemental calcium

There are a number of interferences that can occur in atomic absorption and other flame spectroscopic methods. Anything that decreases the number of neutral atoms in the flame will decrease the absorption signal. Chemical interference is the most commonly encountered example of depression of the absorption signal. Here, the element of interest reacts with an anion in solution or with a gas in the flame to produce a stable compound in the flame. For example, calcium, in the presence of phosphate, will form the stable pyrophosphate molecule. Refractory elements will combine with 0 or OH radicals in the flame to produce stable monoxides and hydroxides. Fortunately, most of these chemical interferences can be avoided by adding an appropriate reagent or by using a hotter flame. The phosphate interferences, for example, can be eliminated by adding 1 % strontium chloride or lanthanum chloride to the solution. The strontium or lanthanum preferentially combines with the phosphate to prevent its reaction with the calcium. Or, EDTA can be added to complex the calcium and prevent its combination with the phosphate. 

Sihca is reduced to siUcon at 1300—1400°C by hydrogen, carbon, and a variety of metallic elements. Gaseous siUcon monoxide is also formed. At pressures of >40 MPa (400 atm), in the presence of aluminum and aluminum haUdes, siUca can be converted to silane in high yields by reaction with hydrogen (15). SiUcon itself is not hydrogenated under these conditions. The formation of siUcon by reduction of siUca with carbon is important in the technical preparation of the element and its alloys and in the preparation of siUcon carbide in the electric furnace. Reduction with lithium and sodium occurs at 200—250°C, with the formation of metal oxide and siUcate. At 800—900°C, siUca is reduced by calcium, magnesium, and aluminum. Other metals reported to reduce siUca to the element include manganese, iron, niobium, uranium, lanthanum, cerium, and neodymium (16). 

Preparation. Hexagonal boron nitride can be prepared by heating boric oxide with ammonia, or by heating boric oxide, boric acid, or its salts with ammonium chloride, alkaU cyanides, or calcium cyanamide at atmospheric pressure. Elemental nitrogen does not react with boric oxide even in the presence of carbon, though it does react with elemental boron at high temperatures. Boron nitride obtained from the reaction of boron trichloride or boron trifluoride with ammonia is easily purified. 

Ununpentium is also known as eka-bismuth because it is homologous to the element bismuth located at the bottom of Group 15 (VA). Its melting point, boihng point, and density are unknown as are many of its other properties. Several isotopes of element 115 were produced by the nuclear reaction that bombarded calcium into a target americium, resulting in the fusion of the calcium nuclei with the americium nuclei to form isotopes of element 115 (ununpentium). 

Calcium reacts with phosphine in an analogous manner as the alkali metals. In liquid ammonia, solid Ca(PH2)2 nNHs is formed with hydrogen evolution 128,280) -pjjg corresponding reaction with a solution of elemental strontium in liquid ammonia does not lead to a uniform product. ... 

CARBIDES. A binary solid compound of carbon and another element. The most familiar carbides are those of calcium, tungsten, silicon, boron, and iron (cemcntitc) Two factors have an important bearing on the properties of carbides (1) the difference in electronegativity between carbon and the second elemenl. and (2) whether the second element is a transition metal. Saltlike carbides of alkali metals are obtained by reaction with acetylene. Those ohlained from silver, copper, and mercury sails are explosive. See also Carbon and Iron Metals, Alloys, and Steels. 

In a composition reaction, two or more reactants form one product. In this composition reaction, two compounds, water and calcium oxide, form one product, calcium hydroxide. In more common composition reactions, two elements form a compound. An example is magnesium reacting with oxygen to form magnesium oxide. 

Reactive electrodes refer mostly to metals from the alkaline (e.g., lithium, sodium) and the alkaline earth (e.g., calcium, magnesium) groups. These metals may react spontaneously with most of the nonaqueous polar solvents, salt anions containing elements in a high oxidation state (e.g., C104 , AsF6 , PF6 , SO CF ) and atmospheric components (02, C02, H20, N2). Note that ah the polar solvents have groups that may contain C—O, C—S, C—N, C—Cl, C—F, S—O, S—Cl, etc. These bonds can be attacked by active metals to form ionic species, and thus the electrode-solution reactions may produce reduction products that are more stable thermodynamically than the mother solution components. Consequently, active metals in nonaqueous systems are always covered by surface films [46], When introduced to the solutions, active metals are usually already covered by native films (formed by reactions with atmospheric species), and then these initial layers are substituted by surface species formed by the reduction of solution components [47], In most of these cases, the open circuit potentials of these metals reflect the potential of the M/MX/MZ+ half-cell, where MX refers to the metal salts/oxide/hydroxide/carbonates which comprise the surface films. The potential of this half-cell may be close to that of the M/Mz+ couple [48],... 

Among the carbides of the group 2 elements, calcium carbide is the best known. It reacts with water, liberating acetylene, and thus is called an acetyUde (equation 12). At one time, this reaction was the main source of HC=CH for oxyacetylene welding. Production of CaC2 peaked at 7 million toimes per year in 1960, bnt declined slightly to 6.2 million toimes in 1985 because acetylene now is obtained from petrochemical processing. 

Reduction to elemental titanium was first commercialized in the 1950s. A successful laboratory method is reduction of the dioxide with excess calcium hydride in a molybdenum boat. The reaction is carried out at 900 °C in a vacuum or an atmosphere of hydrogen (equation 1). Extremely pure titanium can be prepared on a laboratory scale by the van Arkel-de Boer method in this method, pure TiLi is vaporized and decomposed on a hot wire in a vacuum. 

The most important characteristic of hard water is its reaction with soap. If distilled or soft water be shaken with a solution of soap a lather or foam is formed immediately. If, however, a dilute solution of soap be added drop by drop to some hard water in a bottle which is stoppered and shaken after each addition, it will be found that no lather is formed at first. The water, at the same time, assumes a turbidity owing to the formation of an insoluble precipitate. Finally, after sufficient soap has been added, a lather will appear. Soaps are sodium salts of fatty acids of high molecular weight, such as sodium oleate CuHggCOONa. The salts of sodium are soluble in water, but those of calcium and magnesium are not and, in hard water, the ions of these elements displace the sodium, giving precipitates of their insoluble fatty acid salts ... 

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