Pure chemical substances

As shown in the previous chapter, the Tableau provided six classes for the genera of pure chemical substances one for the genera of simple substances and five for the genera of different types of compounds. This most principal feature of its classifica-tory strucmre relied on two premises. It was first assumed that the chemical substances in question could be divided into either simple substances or compounds and second, that all chemical compounds were classified according to their chemical composition. Classification according to composition is, therefore, the most fundamental chemical principle embodied in the classificatory structure of the table. 

The premise that all of the substances comprised by the Tableau s classificatory structure are either simple substances or compounds is not only an elementary presupposition for classification according to composition, it is at the same time the basic criterion for the selection of chemical substances that can be classified within this framework. The substances assembled in the tableau of the Methode represent a highly selected group of substances compared to the archipelago of materials— 

1 As we will see in the next chapter, classification according to properties also occurred in the 1787 table, though only as a complementary feature. 

For a historical understanding of this selection, its tacit character is particularly telling. In the text of the Methode it was not mentioned, let alone clarified, that the classificatory structure of the table implies a selection of chemical substances. Its authors argued neither for such a selection nor for the underlying distinction of the selected chemical substances from others. They evidently felt no need to justify this selection and, as a matter of fact, none of their contemporaries asked them to do so. From these circumstances one can conclude that both the tacit selection and its tacit criterion were not introduced by them for the first time. Rather, they proposed a new nomenclature and classification for a selection of substances that had been singled out and well established as a particular subject matter of chemical investigation independent of and long before their classificatory attempt. 

The particular field of chemical theory and practice to which their selection of substances pertained is plainly indicated by the chemical operations connecting the substances of the table s classes. Focusing on the classes that were well-established before the Methode—Xht classes of the traditional salifiable bases (I/c-e), the acids (Ill/b), the metal oxides or metal calces (in/c), the salts (V/b-c), and the alloys (VI/c)—we find three basic types of chemical processes involved first, those in acid solutions, mainly in connection with the production or decomposition of salts second, calcination of metals and reduction of metal calces and third, the combination of metals into alloys. 

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Reagent A pure chemical substance that is used to make new products or is used in chemical tests to measure, detect, or examine other substances. 

We developed the concept of the mole In terms of pure chemical substances, but many chemical reactions take place In solution. To treat solution reactions quantitatively, we need ways to apply the mole concept to solutions. A substance used to dissolve solutes Is a solvent, and a pure substance dissolved In solution Is a solute. Most of the time, the solvent Is a liquid and Is present In much larger quantities than any solutes. 

The reason for this varied behaviour is not difficult to find. A population of bacteria does not possess the uniformity of properties inherent in pure chemical substances. This fact, together with the varied manner in which bactericides exert their effect and the complex nature of the bacterial cell, should provide adequate and satisfying reasons why the precise theories of reaction kinetics should have failed to explain the disinfeclion process. 

Making a measurement of any kind involves comparing the unknown (i.e. the test sample being measured) with a standard. The standard provides the link to the measurement scale being used (e.g. a ruler to measure length, a standard weight to measure mass, a pure chemical substance to determine the amount of a compound present). This is illustrated in Figure 5.1. 

The fundamental unit in chemical measurement is the mole - amount of substance. A mole is the amount of a substance that contains as many atoms, molecules, ions or other elementary units as the number of atoms in 0.012 kg of carbon 12 (12C). It is the only dimensionless SI unit. In practical terms, it is almost impossible to isolate a mole of pure substance. Substances with a purity of better than 99.9% are rare one exception is silver, which can be obtained with a purity of 99.9995% which is referred to as five nines silver . Another problem is that it is not always possible to isolate all of the analyte from the sample matrix, and the performance of the chemical measurement may be matrix-dependent - a given response to a certain amount of a chemical in isolation may be different from the response to the same amount of the chemical when other chemicals are present. If it is possible to isolate quantitatively all of the analyte of interest from the accompanying sample matrix, then a pure chemical substance may be used for calibration. The extent to which the analyte can be recovered from the sample matrix will have been determined as part of the method validation process (see Chapter 4, Section 4.6.3). 

Section 5.2 introduced the subject of metrological traceability and calibration and the use of pure chemical substances and reference materials in achieving trace-ability. Reference materials are used as transfer standards. Transfer standards are used when it is not possible to have access to national or international standards or primary methods. Transfer standards carry measurement values and can be... 

Although considered a basic technique, ultraviolet-visible (UV-vis) is perhaps the most widely used spectrophotometric technique for the quantitative analysis of pure chemical substances such as APIs in pharmaceutical analysis. For pharmaceutical dosage forms that do not present significant matrix interference, quantitative UV-vis measurements may also be made directly.114,115 It is estimated that UV-vis-based methods account for 10% of pharmacopoeia assays of drug substances and formulated products.116... 

Karyakin, Yu. V. and Angelov, I. I. Chistye khimicheskie veshchestva (Pure Chemical Substances) (Moscow Khimiya, 1974). 

To explore the ramifications of the phase rule (7.6), we shall first consider the phase equilibria of pure chemical substances (c = 1). Subsequent sections will examine the more complex behavior of binary (c = 2) and ternary (c = 3) multiphase systems. 

PETN is a white crystalline substance which melts at 140-141 °C. The melting point of the pure chemical substance is 141.3°C. Its boiling point was reported by Belayev and Yuzefovich [7] to be... 

They can be pure chemical substances, blends or synthetic mixtures, simulates or artefacts, spiked or unspiked real-life samples. 

Physicochemical properties are required in their own right as part of the description of the characteristics of a chemical (e.g., for regulatory submission), or as one of the three components of quantitative structure-activity relationships (QSARs) (see Chapter 1, Figure 1.1 and Figure 1.2 for more details). While the properties of a pure chemical substance may be measured, the computation of physicochemical properties has many advantages. These include the speed and low cost of calculation and, more importantly, the fact that calculation may be performed for chemicals that are not available. 

If we disregard electronic phenomena, ignore the residual coupling terms between atomic quasi-particles, and specialize to the case of a single kind of composite quasi-particle, i.e. a pure chemical substance, at low density, the dynamical map P = W(X) allows us to write the Hamiltonian iC in the form,... 

The GHS applies to pure chemical substances, their dilute solutions and to mixtures of chemical substances. Articles as defined in the Hazard Communication Standard (29 CFR 1910.1200) of the US Occupational Safety and Health Administration, or by similar definition, are outside the scope of the system. 

This Database is particularly useful for the identification of materials, either pure chemical substances or mixtures, such as the deposit scraped from the inside of the smokestack of an industrial factory. A certain number of these diffraction peaks in the diffraction pattern of the compound or deposit are compared, both with respect to scattering angle and relative intensity with the substances already in the Powder Diffraction File. Often good analyses of mixtures can be made in this way. 

Sections 4 and 5, Empirical Formula and Molecular Weight and Structural Formula, are self-explanatory. Many excipients are not pure chemical substances, in which case their composition is described either here or in Section 8. 

TRUE PARTICLE DENSITY when the volume measured excludes both open and closed pores. This is the density of the solid material of which the particle is made for pure chemical substances, organic or inorganic, this is the density quoted in reference books of physical/chemical data. 

Tlie sample tnay consist of (i) a pure chemical substance, (ii) a pharmaceutical preparation (tablet, capsule, or mixture), (iii) blood, urine, vomit, or stomach washings, or (iv) body tissues—liver, kidney, or brain, together with stomach and intestines and their contents. 

The mole volumes of many simple pure chemical substances at the absolute zero point, the melting and boiling points at atmospheric pressure, and the critical point, respectively, are as 1 1.21 1.48 3.78 hence volume relationships are basic in the physical definition of solid and liquid states. 

Crystallization from solution is important industrially because of the variety of materials that are marketed in the crystalline form. Its wide use has a twofold basis a crystal formed from an impure solution is itself pure (unless mixed crystals occur), and crystallization affords a practical method of obtaining pure chemical substances in a satisfactory condition for packaging and storing. 

Electron configuration The arrangement of electrons in an atom or molecule Element A pure chemical substance consisting of atoms that have the same atomic number... 

If any pure chemical substance is divided into two pieces and then one piece is again divided into two and the process is repeated so that the size of the piece is continually decreasing, eventually the substance cannot be sub-divided any further without being decomposed. At this stage, we have the smallest particle of that substance in existence. 

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