Chemical formulas defined

Chemical food preservation, 12 85-86 Chemical formula, defined, 21 336 Chemical fossils, 18 571 Chemical gas scavengers, 12 77 Chemical gel stabilization, 23 71 Chemical-grade limestone, 15 27 Chemical-grade propylene, product specification for, 20 1111 Chemical hazards, 21 833-846... 

A model is one of the main outcomes of ary scientific enquiry and hence is a major contributor to philosophy of science. A model may be defined as a simplified representation of a phenomenon (an object, system, event, process) or idea produced for the specific purpose of providing an explanation of that entity, the most important outcomes of which are the production of successful predictions of how it will behave under a range of circumstances (Gilbert, Boulter, Elmer, 2000). Entities can be modelled at the three levels at the macroscopic, by representing some of the aspects of the entity that can be seen at the sub-microscopic, by representing the ideas produced to explain the constitution and behaviour of the particles that constitute the entity and at the symbolic, by representing the symbols created to simplify the reference to such particles (as, for instance, chemical formulae and chemical equations). 

Complex ions, also called coordination complexes, have well-defined stoichiometries and structural arrangements. Usually, the formula of a coordination complex is enclosed in brackets to show that the metal and all its ligands form a single structural entity. When an ionic coordination complex is isolated from aqueous solution, the product is composed of the complex ion and enough counter-ions to give a neutral salt. In the chemical formula, the counter-ions are shown outside the brackets. Examples include the sulfate salt of [Ni (NH3)g, ... 

The very basis of the kinetic model is the reaction network, i.e. the stoichiometry of the system. Identification of the reaction network for complex systems may require extensive laboratory investigation. Although complex stoichiometric models, describing elementary steps in detail, are the most appropriate for kinetic modelling, the development of such models is time-consuming and may prove uneconomical. Moreover, in fine chemicals manufacture, very often some components cannot be analysed or not with sufficient accuracy. In most cases, only data for key reactants, major products and some by-products are available. Some components of the reaction mixture must be lumped into pseudocomponents, sometimes with an ill-defined chemical formula. Obviously, methods are needed that allow the development of simple... 

Widespread medicinal use of colloidal bismuth subcitrate (CBS) has prompted extensive studies of bismuth compounds involving the citrate anion. Bismuth citrate is essentially insoluble in water, but a dramatic increase in solubility with increasing pH has been exploited as a bio-ready source of soluble bismuth, a material referred to as CBS. Formulation of these solutions is complicated by the variability of the bismuth anion stoichiometry, the presence of potassium and/ or ammonium cations, the susceptibility of bismuth to oxygenation to Bi=0, and the incorporation of water in isolated solids. Consequently, a variety of formulas are classified in the literature as CBS. Solids isolated from various, often ill-defined combinations of bismuth citrate, citric acid, potassium hydroxide, or ammonium hydroxide have been assigned formulas on the basis of elemental analysis data or by determination of water and ammonia content, but are of low significance in the absence of complementary data other than thermal analysis (163), infrared spectroscopy (163), or NMR spectroscopy (164). In this context, the Merck index lists the chemical formula of CBS as KgfNHJaBieOafOHMCeHsCbh in the 11th edition (165), but in the most recent edition provides a less precise name, tripotassium dicitrato bismuthate (166). 

ORR rate constant as defined by eq 61, 1/s ORR rate constant in Figure 11, cm/s thermal conductivity of phase k, J/cm K relative hydraulic permeability saturated hydraulic permeability, cm electrokinetic permeability, cm catalyst layer thickness, cm parameter in the polarization equation (eq 20) loading of platinum, g/cm molecular weight of species i, g/mol symbol for the chemical formula of species i in phase k having charge Zi... 

For nonmolecular substances like sodium chloride, the use of the word mole, with its connotation of molecules, is inappropriate. A comparable unit, the gram formula weight, is used it is defined as the sum in grams of the atomic weights of all the atoms in the chemical formula of the substance. For sodium chloride (NaCl), one gram formula weight is calculated as... 

Occasionally, you may be asked to calculate the mole fraction of a solution, which is the ratio of the number of moles of either solute or solvent in a solution to the total number of moles of solute and solvent in the solution. By the time chemists defined this quantity, however, they had finally acknowledged that they had too many m variables, and they gave it the variable X. Of course, chemists still need to distinguish between the mole fractions of the solute and the solvent, which unfortunately both start with the letter s. To avoid further confusion, they decided to abbreviate solute and solvent as A and B, respectively, in the general formula, although in practice, the chemical formulas of the solute and solvent eire usually written as subscripts in place of A and B. For example, the mole fraction of sodium chloride in a solution would be written as... 

The first step to making the theory more closely mimic the experiment is to consider not just one structure for a given chemical formula, but all possible structures. That is, we fully characterize the potential energy surface (PES) for a given chemical formula (this requires invocation of the Born-Oppenheimer approximation, as discussed in more detail in Chapters 4 and 15). The PES is a hypersurface defined by the potential energy of a collection of atoms over all possible atomic arrangements the PES has 3N — 6 coordinate dimensions, where N is the number of atoms >3. This dimensionality derives from the three-dimensional nature of Cartesian space. Thus each structure, which is a point on the PES, can be defined by a vector X where... 

Compounds that have the same chemical formula but have different structures are called isomers. For example, fructose, glucose, mannose, and galactose are all isomers of each other, having the same chemical formula, C6H1206. If two monosaccharides differ in configuration around only one specific carbon atom (with the exception of the carbonyl carbon, see anomers below), they are defined as epimers of each other. (Of course, they are also isomers ) For example, glucose... 

The C.I. Constitution number is given in this paper as a guide to references for synthesis in the Colour Index. Any duplication of these syntheses should be attempted only under the supervision of an experienced chemist who is aware of the latest ecological, toxicological, and safety requirements. These requirements must be constantly observed even if attention is not explicidy drawn to them. A further point to note is that dye chemists often write the free sulfonic acid form, even if they have obtained a salt. The reason is that the dyes are often not completely neutral or may not be a defined salt. This commonly arises when potassium or sodium salts are involved, and therefore the free sulfonic acid formula is frequentiy used as a general term. A sulfonate salt does not influence the color as such, but water solubility is affected. Consequently, for pigments the cation is always given in the chemical formula. 

The mole is associated with a specific chemical entity as defined by its chemical formula [15], Its structural formula, isotopic composition, isomeric form, crystal structure, or chirality may have to be given in order to completely specify the entity of interest. The achievable uncertainty of amount-of-substance measurement is limited by that of its apparent molar mass. This consideration affects not only measurements on entities with variable molar mass, but those on pure substances. It is related to the traditional and important concern about purity. 

The term active has historically been used to define protovitamins (dimers) that resulted in material biologically active with respect to humans when cleaved (in this case Vitamin AQ It is only infrequently that an author will introduce a caveat that some protovitamin A material can be considered active because it results in Vitamin A2. There has been virtually no previous literature regarding Vitamin A3. In this work, a protovitamin can be cleaved to form any one of the three types of Vitamin A. Many are dimers that can be cleaved to form two monomers of Vitamin A. The resulting monomers need not be the same type of Vitamin A. When discussing the term active in this work, it is more closely aligned to the phylum and order of the animal than to the chemical formula of the compound. 

Figure 4. Plot of Ln D versus Ln (molecular weight) for a series of low-molecular-weight linear dimethylsiloxanes in polydimethylsiloxane fluid. Numbers at each data point refer to N, defined by chemical formula. Data from Ref. 10.

The second class comprises conventional solids, defined by a chemical formula, but whose property requirements are very minimal. In this class we included lignin, cellulose, mannan, galactan, xylan, arabinan and the biomass. The properties specified in the database include molecular weight, heat of formation, solid molar volume, and solid heat capacity. 

Elements are defined by the structure of their atoms, determined by the number of each type of subatomic particle present. Each element has been given a name, which is shown in Figure 1.1 as a two-letter abbreviation. These are the abbreviations that are used to write out chemical formulae. 

In mineralogy, the same terms are used, but with different meaning. The holotype of a mineral species is the specimen from which the characterizing data was obtained, such as unit cell dimensions and shape, chemical formula, etc. Type specimens rarely exist for species defined before 1800. Since most modem analytical methods are, at least in part, destructive, sometimes the only existing sample is destroyed or processed in order to obtain the data needed to define a new species. 

Mineral species a mineral substance having a specific chemical formula and characteristic physical and optical properties that distinguish it from all others defined by composition and crystal structure. 

Cellulose, Microcrystalline, 95 Cellulose, Modified, (SI) 14 Cellulose, Powdered, 96 Centrifuge, Defined, 4 Ceric Ammonium Nitrate TS, 851 Ceric Sulfate, 0.01 N, 856 Ceric Sulfate, 0.1 N, 856 Chamomile Oil, English Type, 98, 578 Chamomile Oil, German Type, 98, 578 Chamomile Oil, Hungarian Type, 98 Changes in Format to the Food Chemicals Codex, Fourth Edition, xv Chemical Formulas and Atomic Weights, 3... 

Identify the materials used and give information on the degree of and criteria for purity, but do not reference standard laboratory reagents. Give the chemical names of all compounds and the chemical formulas of compounds that are new or uncommon. Use meaningful nomenclature that is, use standard systematic nomenclature where specificity and complexity require, or use trivial nomenclature where it will adequately and unambiguously define a well-established compound. 

A benzenoid isomer is defined by a pair of invariants (n, s) and usually written as the chemical formula C Hs. Here n is the total number of vertices, corresponding to the number of carbon (C) atoms, while s is the number of vertices of degree two (on the perimeter), corresponding to the number of secondary carbon atoms (hence the symbol s). This number (s) is also the number of hydrogens (H). 

It is instructive to compare the atom economies of the two pathways. Atom economy is a measure of the efficiency of a chemical process, defined in percentage terms as x (formula wt. of atoms utilized)/(formula wt. of all reactants). For the old six-step ibuprofen synthesis the atom economy was only 40% (with MeC02H, EtOH, NaCl, Et0C02H, 2H2O and NH3 as waste). This is dramatically improved to 77% for the new three-step route with only MeC02H as a by-product from the first step. Recovery and use of this increases the atom economy to 99%. Additionally, the catalytic amounts of HF and Pd complex used in the BHC process are recovered and reused, whereas stoichiometric quantities of AICI3 hydrate were produced as waste by the old route. 

When the composition of a crystal is defined by a distinct chemical formula e.g., Si02), it is known as a stoichiometric compound. If the composition of the crystal is altered upon doping or thermal treatment, the resulting solid may deviate from the original chemical formula, forming a nonstoichiometric solid. Nonstoichiometry and the existence of point defects in a solid are often closely related. For instance, the formation of x anion vacancies per each quartz unit cell will result in the nonstoichiometric compound Si02-x ... 

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