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Anhydrous
A substance is anhydrous if it contains no water. Many processes in chemistry can be impeded by the presence of water; therefore, it is important that water-free reagents and techniques are used. In practice, however, it is very difficult to achieve perfect dryness; anhydrous compounds gradually absorb water from the atmosphere so they must be stored carefully. Solids Many salts and solids can be dried using heat, or under vacuum. Desiccators can also be used to store reagents in dry conditions. Common desiccants include phosphorus pentoxide and silica gel. Chemists may also require dry glassware for sensitive reactions. This can be achieved by drying glassware in an oven, by flame, or under vacuum. Dry solids can be produced by freeze-drying, which is also known as lyophilization. Liquids or solvents In many cases, the presence of water can prevent a reaction from happening, or cause undesirable products to form. To prevent this, anhydrous solvents must be used when perfor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammonia
Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous waste, particularly among aquatic organisms, and it contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to 45% of the world's food and fertilizers. Around 70% of ammonia is used to make fertilisers in various forms and composition, such as urea and Diammonium phosphate. Ammonia in pure form is also applied directly into the soil. Ammonia, either directly or indirectly, is also a building block for the synthesis of many pharmaceutical products and is used in many commercial cleaning products. It is mainly collected by downward displacement of both air and water. Although common in nature—both terrestrially and in the outer planets of the Solar System—and in wide use, ammonia i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnesium Sulfate
Magnesium sulfate or magnesium sulphate (in English-speaking countries other than the US) is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, soluble in water but not in ethanol. Magnesium sulfate is usually encountered in the form of a hydrate , for various values of ''n'' between 1 and 11. The most common is the heptahydrate , known as Epsom salt, which is a household chemical with many traditional uses, including bath salts. The main use of magnesium sulfate is in agriculture, to correct soils deficient in magnesium (an essential plant nutrient because of the role of magnesium in chlorophyll and photosynthesis). The monohydrate is favored for this use; by the mid 1970s, its production was 2.3 million tons per year. The anhydrous form and several hydrates occur in nature as minerals, and the salt is a significant component of the water from some springs. Hydrates Magnesi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrate
In chemistry, a hydrate is a substance that contains water or its constituent elements. The chemical state of the water varies widely between different classes of hydrates, some of which were so labeled before their chemical structure was understood. Chemical nature Inorganic chemistry Hydrates are inorganic salts "containing water molecules combined in a definite ratio as an integral part of the crystal" that are either bound to a metal center or that have crystallized with the metal complex. Such hydrates are also said to contain '' water of crystallization'' or ''water of hydration''. If the water is heavy water in which the constituent hydrogen is the isotope deuterium, then the term ''deuterate'' may be used in place of ''hydrate''. A colorful example is cobalt(II) chloride, which turns from blue to red upon hydration, and can therefore be used as a water indicator. The notation "''hydrated compound''â‹…''n''", where ''n'' is the number of water molecules per for ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Standard Conditions Of Temperature And Pressure
Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union of Pure and Applied Chemistry (IUPAC) and the National Institute of Standards and Technology (NIST), although these are not universally accepted standards. Other organizations have established a variety of alternative definitions for their standard reference conditions. In chemistry, IUPAC changed its definition of standard temperature and pressure in 1982: * Until 1982, STP was defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 1 atm (101.325 kPa). * Since 1982, STP has been defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly 105 Pa (100 kPa, 1 bar). STP should not be confused with the standard state com ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Desiccant
A desiccant is a hygroscopic substance that is used to induce or sustain a state of dryness (desiccation) in its vicinity; it is the opposite of a humectant. Commonly encountered pre-packaged desiccants are solids that absorb water. Desiccants for specialized purposes may be in forms other than solid, and may work through other principles, such as chemical bonding of water molecules. They are commonly encountered in foods to retain crispness. Industrially, desiccants are widely used to control the level of water in gas streams. Types of desiccants Although some desiccants are chemically inert, others are extremely reactive and require specialized handling techniques. The most common desiccant is silica gel, an otherwise inert, nontoxic, water-insoluble white solid. Tens of thousands of tons are produced annually for this purpose. Other common desiccants include activated charcoal, calcium sulfate, calcium chloride, and molecular sieves (typically, zeolites). Desicca ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Base Anhydride
A base anhydride is an oxide of a chemical element from group 1 or 2 (the alkali metals and alkaline earth metals, respectively). They are obtained by removing water from the corresponding hydroxide base. If water is added to a base anhydride, a corresponding hydroxide salt can be re-formed. Base anhydrides are not Brønsted–Lowry bases because they are not proton acceptors. However, they are Lewis bases, because they will share an electron pair with some Lewis acids, most notably acidic oxides.Principles of Modern Chemistry, 7th Edition. David Oxtoby, H. P. Gillis, Alan Campion. Published by Cengage Learning. Page 675-676. They are potent alkalis and will produce alkali burns on skin, because their affinity for water (that is, their affinity for being slaked) makes them react with body water. Examples * Quicklime (calcium oxide) is a base anhydride. It reacts with skin to become hydrated lime ( calcium hydroxide), which is a strong base, chemically akin to lye. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Acidic Oxide
An acidic oxide is an oxide that either produces an acidic solution upon addition to water, or acts as an acceptor of hydroxide ions effectively functioning as a Lewis acid. Acidic oxides will typically have a low pKa and may be inorganic or organic. A commonly encountered acidic oxide, carbon dioxide produces an acidic solution (and the generation of carbonic acid) when dissolved. The acidity of an oxide can be reasonably assumed by its accompanying constituents. Less electronegative elements tend to form basic oxides such as sodium oxide and magnesium oxide, whereas more electronegative elements tend to produce acidic oxides as seen with carbon dioxide and phosphorus pentoxide. Some oxides like aluminium oxides are amphoteric. Acidic oxides are of environmental concern. Sulfur and nitrogen oxides are considered air pollutants as they react with atmospheric water vapour to produce acid rain. Examples Carbonic acid is an illustrative example of the Lewis acidity of an aci ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Air-free Technique
Air-free techniques refer to a range of manipulations in the chemistry laboratory for the handling of compounds that are air-sensitive. These techniques prevent the compounds from reacting with components of air, usually water and oxygen; less commonly carbon dioxide and nitrogen. A common theme among these techniques is the use of a fine (100–10−3 Torr) or high (10−3–10−6 Torr) vacuum to remove air, and the use of an inert gas: preferably argon, but often nitrogen. The two most common types of air-free technique involve the use of a glovebox and a Schlenk line, although some rigorous applications use a high-vacuum line. In both methods, glassware (often Schlenk tubes) are pre-dried in ovens prior to use. They may be flame-dried to remove adsorbed water. Prior to coming into an inert atmosphere, vessels are further dried by ''purge-and-refill'' — the vessel is subjected to a vacuum to remove gases and water, and then refilled with inert gas. This cycle is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dean–Stark Apparatus
upDean–Stark apparatus setup for an azeotrope with a solvent whose density is ''less than'' that of water: The Dean–Stark apparatus, Dean–Stark receiver, distilling trap, or Dean–Stark Head is a piece of laboratory glassware used in synthetic chemistry to collect water (or occasionally other liquid) from a reactor. It is used in combination with a reflux condenser and a distillation flask for the separation of water from liquids. This may be a continuous removal of the water that is produced during a chemical reaction performed at reflux temperature, such as in esterification reactions. It was invented by the American chemists Ernest Woodward Dean (1888–1959) and David Dewey Stark (1893–1979) in 1920 for determination of the water content in petroleum. Function left, A Dean–Stark apparatus in use; aluminium foil is used to reduce heat losses Two types of Dean–Stark traps exist – one for use with solvents with a density ''less'' than that of water and anoth ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrochloric Acid
Hydrochloric acid, also known as muriatic acid, is an aqueous solution of hydrogen chloride. It is a colorless solution with a distinctive pungent smell. It is classified as a strong acid. It is a component of the gastric acid in the digestive systems of most animal species, including humans. Hydrochloric acid is an important laboratory reagent and industrial chemical. History In the early tenth century, the Persian physician and alchemist Abu Bakr al-Razi ( 865–925, Latin: Rhazes) conducted experiments with sal ammoniac ( ammonium chloride) and vitriol (hydrated sulfates of various metals), which he distilled together, thus producing the gas hydrogen chloride. In doing so, al-Razi may have stumbled upon a primitive method for producing hydrochloric acid, as perhaps manifested in the following recipe from his ("The Book of Secrets"): However, it appears that in most of his experiments al-Razi disregarded the gaseous products, concentrating instead on the color c ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hydrogen Chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride gas and hydrochloric acid are important in technology and industry. Hydrochloric acid, the aqueous solution of hydrogen chloride, is also commonly given the formula HCl. Reactions Hydrogen chloride is a diatomic molecule, consisting of a hydrogen atom H and a chlorine atom Cl connected by a polar covalent bond. The chlorine atom is much more electronegative than the hydrogen atom, which makes this bond polar. Consequently, the molecule has a large dipole moment with a negative partial charge (δ−) at the chlorine atom and a positive partial charge (δ+) at the hydrogen atom. In part because of its high polarity, HCl is very soluble in water (and in other polar solvents). Upon contact, and HCl combine to form hydronium cations a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ammonia Solution
Ammonia solution, also known as ammonia water, ammonium hydroxide, ammoniacal liquor, ammonia liquor, aqua ammonia, aqueous ammonia, or (inaccurately) ammonia, is a solution of ammonia in water. It can be denoted by the symbols NH3(aq). Although the name ammonium hydroxide suggests an alkali with composition , it is actually impossible to isolate samples of NH4OH. The ions and OH− do not account for a significant fraction of the total amount of ammonia except in extremely dilute solutions. Basicity of ammonia in water In aqueous solution, ammonia deprotonates a small fraction of the water to give ammonium and hydroxide according to the following equilibrium: : NH3 + H2O NH4+ + OH−. In a 1 M ammonia solution, about 0.42% of the ammonia is converted to ammonium, equivalent to pH = 11.63 because H4+ = 0.0042 M, H− = 0.0042 M, H3 = 0.9958 M, and pH = 14 + log10 H− = 11.62. The base ionization constant is : ''K''b = H4+OH−] / H3= 1.77. Sa ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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