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Home >> Chemistry Dictionary >> Bomb Calorimeter Bordeaux Mixture
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Boiling point (b.p). The temperature at which the saturated vapour pressure of a liquid equals the external atmospheric pressure. As a consequence, bubbles form in the liquid and the temperature remains constant unit, all the liquid has evaporated. As the boiling point of a liquid depends on the external atmospheric pressure, boiling points are usually quoted for standard atmospheric pressure (760 mm-Hg = 101 325 Pa).
Boiling point diagram. A graph showing equilibrium compositions of liquid and vapour plotted against temperature for a two-component system at any given pressure.
Baltzmann constant. Symbol K. Refers to the ration of the universal gas constant (R) to the Avogadro constant (Na). It may be thought of, therefore, as the gas constant per molecular.
K=R/NA = 1.380622 × 10-23 JK-1
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Boiling point, elevation of. The increase in boiling of a solution, compared with that of the pure solvent, due to a dissolved substance. The elevation of boiling point is proportional to the weight of a particular solute. Molecular proportions of different solutes produce the same elevation. The following values represent the elevation of boiling point produced in different solvents by dissolving 1 mol of any solute in 100g of solvent. This is known as the molecular elevation of boiling point.
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Solvent |
Molecular elevation |
Water |
5.2° |
Chloroform |
38.8° |
Ether |
21.1° |
Acetone (propanone) |
17.2° |
Benzene |
25.7° |
Alcohol (ethanol) |
11.5° |
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Bomb calorimeter. An apparatus for measuring the heat of combustion of a substance in which the heat liberated, when the sample is ignited in an atmosphere, e.g. of oxygen under pressure, is measured. Used to obtain precise thermochemical data.
Bone meal. Ground animal bones used as a phosphorous fertilizer.
Borane. Formally BH3, i.e. borane pyridine, is H3BNC5H9. BH3 is only stable when complexed.
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Bond. The linkage between atoms in molecules and between molecules and ions in crystals.
Bond energy. The energy required to break a particular bond and, precisely to produce the products in particular electronic states. Bond energies of multiple bonds are generally greater than those of single bonds.
Bond length. The mean internuclear distance between two Atoms forming a chemical bond. Even for the same atomic species the bond length will differ from one compared to another. For example, the carbon hydrogen length in benzene differs from that in cyclohexane.
Borates. Metal salts of tetraboric acid, H2B4O7 or metabolic and HBO2. They are found is nature. Calcium borate is used in the manufacture of ceramics, zinc borate in the textile industry.
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Bordeaux mixture. A mixture of slaked lime and copper sulphate solution. Used as a furgicide.
Boric acid. Any of a number of acids containing boron and oxygen. Used without qualification the term applies to the compound H3BO3 (which is also called arthoboric acid or, technically, trioxoboric (III) acid). This is a white or colourless solid that is soluble in water and ethanol; triclinid; r.d. 1.435; m.p 169°C. It occurs naturally in the condensate from volcanic steam vents (suffioni). Commercially, it is made by treating borate minerals (e.g. kernite, Na2B4O7. 4H2O) with sulphuric acid followed by recrystallization.
In the solid there is considerable hydrogen bonding between H3BO2 molecules resulting in a layer structure, which accounts for the easy cleavage of the crystals. H3BO3 molecules also exist in dilute solutions but in more concentrated solutions polymeric acids and ions are formed (e.g. E4B4O7; pyroboric acid or tetrahydroxodiboric (III) acid). The compound is a very week acid but also acts as a Lewis acid in accepting hydroxide ions.
B(OH)3 + H2O = B (OH)4 + H+
If solid boric acid is heated is loses water and transforms to another acid at 300°C.
Boric acid is used in the manufacture of glass (borosilicate glass), glazes and enamels, leather, paper, adhesives, and explosives. It is widely used (particularly in the USA) in detergents, and because of the ability of fused boric acid to dissolve other metal oxides it is used as a flux in brazing and welding. Of its mild antiseptic properties it is used in the pharmaceutical industry and as a food preservative.
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