أكتوبر 10th, 2018

 

Acid Halid

One of a large group of organic substances possessing the halocar­bonyl group,

in which X stands for fluorine, chlorine, bromine, or iodine. The terms acyl and aroyl halides refer to aliphatic or aromatic derivatives, respectively.

The great inherent reactivity of acid halides precludes their free existence in nature; all are made by synthetic processes. In general, acid…

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Acetylene

An organic compound with the formula C2H2 or HC≡CH. The first member of the alkynes, acetylene is a gas with a narrow liquid range; the triple point is -81 °C (-114°F). The heat of formation (ΔHf) is +227 kilojoules/mole, and acetylene is the most endothermic compound per carbon of any hydrocarbon. The compound is thus extremely energy-rich and can decompose with explosive force. At one time acetylene was…

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Acid base indicators

A substance that reveals, through characteristic color changes, the degree of acidity or basicity of solutions. Indicators are weak organic acids or bases which exist in more than one structural form (tautomers) of which at least one form is colored. Intense color is desirable so that very little indicator is needed; the indicator itself will thus not affect the acidity of the solution.

Acid-base indicators are commonly employed…

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aceton

A chemical compound, CH3COCH3. A colorless liquid with an ethereal odor, it is the first member of the homologous series of aliphatic ketones. Its physical properties include boiling point 56.2°C (133.2°F). melting point -94.8°C (-138.6°F). and specific gravity 0.791.

Acetone is used as a solvent for cellulose ethers, cellulose acetate, cellulose nitrate, and other cellulose esters. Cellulose acetate is spun from acetone solution. Lacquers, based on cellulose esters,…

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Acetic Acid

A colorless, pungent liquid, CH3COOH, melting at 16. 7°C and boil­ing at 118.0°C. Acetic acid is the sour principle in vinegar. Concentrated acid is called glacial acetic acid because of its readiness to crystallize at cool temperatures.

Acetic acid is manufactured by three main routes: butane liquid-phase catalytic ox­idation in acetic acid solvent, palladium-copper salt-catalyzed oxidation of ethylene in aqueous solution, and methanol carbonylation in the presence of…

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Acid anhydride

One of an important class of reactive organic compounds de­rived from acids via formal intermolecular dehydration.

Anhydrides of straight-chain acids containing from 2 to 12 carbon atoms are liquids with boiling points higher than those of the parent acids. They are relatively insoluble in cold water and are soluble in alcohol, ether, and other common organic solvents. The lower members are pungent, corrosive, and weakly lacrimatory.

Anhydrides from…

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Acetal

A geminal diether (R1 = H). Ketals, considered a subclass of acetals, are also geminal diethers (R1 = C, aliphatic or aromatic). Acetals are (1) independent structural units or a part of certain biological and commercial polymers, (2) blocking or protect­ing groups for complex molecules undergoing selective synthetic transformations, and (3) entry compounds for independent organic chemical reactions.

Acetals are easily prepared by the reaction of aldehydes with…

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Acid and base

Two interrelated classes of chemical compounds, the precise definitions of which have varied considerably with the development of chemistry. Some of these controversies are still unresolved.

Acids initially were defined only by their common properties as substances which had a sour taste, dissolved many metals, and reacted with alkalies (or bases) to form salts. For a time it was believed that a common constituent of all acids was…

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Accelerator mass spectrometry

The use of a combination of mass spectrometers and an accelerator to measure the natural abundances of very rare radioactive isotopes. These abundances are frequently lower than parts per trillion. The most important applications of accelerator mass spectrometry are in archeological and geophysical studies, as, for example, in radiocarbon dating by the counting of the rare carbon-14 (radiocarbon; 14C ) isotope.

The advantage of counting the radioactive atoms…

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