أكتوبر 18th, 2018

 

Antimony

Antimony A chemical element, symbol Sb, atomic number 51. Antimony is not a naturally abundant element; it is occasionally found native, often in isomorphous mixture with arsenic, as allemonite. The symbol Sb is derived from the Latin name stibium.

The element is dimorphic, existing as a yellow, metastable form composed of Sb4 molecules, as in antimony vapor and the structural unit in yellow antimony; and a gray, metallic…

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Analytical chemistry

Analytical chemistry The science of chemical characterization and measure­ment. Qualitative analysis is concerned with the description of chemical composition in terms of elements, compounds, or structural units, whereas quantitative analysis is concerned with the measurement of amount.

Analytical chemistry, once limited to the determination of chemical composition in terms of the relative amounts of elements or compounds in a sample, has been expanded to involve the spatial distribution…

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Ammonium Salt

Ammonium salt A product of a reaction between ammonia, NH3, and various acids. The general reaction for formation is NH3 + HX –+ NH2X. Examples of ammo­nium salts are ammonium chloride, NH4Cl, ammonium nitrate, NH4NO3,  These compounds are ad­dition products of ammonia and the acid. For this reason, their formulas are sometimes written as X.

All ammonium salts decompose into ammonia and the acid when heated. Their stability,…

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Ammonia

Ammonia The most familiar compound composed ‘of the elements nitrogen and hydrogen, NH3. It is formed as a result of the decomposition of most nitrogenous organic material, and its presence is indicated by its pungent and irritating odor.

Ammonia has a wide range of industrial and agricultural applications. Examples of its use are the production of nitric acid and ammonium salts, particularly the sulfate, nitrate, carbonate, and chloride,…

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Aspirin

Aspirin The acetyl ester of salicylic acid, also known as 2-(acetyloxy)-benzoic acid and acetylsalicylic acid (see structure below). Aspirin is prepared by the acetylation of salicylic acid with acetic anhydride.

Aspirin is effective as an analgesic, antipyretic, and anti-inflammatory drug. It pre­vents the aggregation of platelets, and there is some evidence that it can prevent stroke. Aspirin, if tolerated, is…

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Argon

Argon A chemical element, Ar, atomic number 18, and atomic weight 39.948. Argon is the third member of group 18 in the periodic table. The gaseous elements in this group are called the noble, inert, or rare gases, although argon is not actually rare. The Earth’s atmosphere is the only natural argon source; however, traces of this gas are found in minerals and meteorites. Argon constitutes 0.934% by…

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Ammine

Ammine One of a group of complex compounds formed by the coordination of ammonia molecules with metal ions and, in a few instances, such as calcium, strontium, and barium, with metal atoms. Although ammines are formally analogous to many salt hydrates, the general characteristics of the group of ammines differ considerably from those of the hydrates. For example, hydrated Co(III) salts are strong oxidizing agents whereas Co(II) ammines…

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Amino acids

Organic compounds possessing one or more basic amino groups and one or more acidic carboxyl groups. Of the more than 80 amino acids which have been found in living organisms, about 20 serve as the building blocks for the proteins. All the amino acids of proteins, and most of the others which occur naturally, are amino acids, meaning that an amino group (-NH2) and a carboxyl group (-COOH)…

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Ascorbic Acid

Ascorbic acid A white, crystalline compound, also known as vitamin C. It is highly soluble in water, which is a stronger reducing agent than the hexose sugars, which it resembles chemically. Vitamin C deficiency in humans has been known for centuries as scurvy.The compound has the structural formula shown below.

The stability of ascorbic acid decreases with increases in temperature…

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