Ordinary chemical means

This conversion cannot easily be carried out on a semi-micro scale by ordinary chemical means. Liberation of an acid from one of its salts by dil. H SO is feasible when the organic acid is insoluble in water (e.g. an aromatic acid) or... 

An element is a substance that cannot be broken down into simpler substances by ordinary chemical means. A chemical compound is a substance made up of two or more elements that have been chemically bonded together. Scientists believe that solid sulfur compounds do not exist on Venus like they do on Earth because, at about 900° Fahrenheit (480° Celsius), the surface temperature on Venus is too hot for them to form in the first place. This temperature is well above the melting point of sulfur (235°F [ 113°C]). Therefore, instead of being incorporated into rocks, the sulfur on Venus continues to float around in the atmosphere in the form of the chemical compound sulfur dioxide (S02). 

Element A substance that cannot be broken down into simpler substances by ordinary chemical means. 

There are two kinds of substances—elements and compounds. Elements are substances that cannot be broken down into simpler substances by ordinary chemical means. Elements cannot be made by the combination of simpler substances. There are slightly more than 100 elements, and every material object in the universe consists of one or more of these elements. Familiar substances which are elements include carbon, aluminum, iron, copper, gold, oxygen, and hydrogen. 

It appeared probable that the reduction of disulfides to mercaptans by means of yeast would be particularly easy, since the two substances can be interconverted quite smoothly by ordinary chemical means. This prediction did not prove to be quite correct. True, Neuberg and Schwenk could reduce a disulfide by means of yeast, but they could not do so with the expected ease. Ethyl disulfide was chosen for the experiment because its boiling point (151°) differs very much from that of ethyl mercaptan (36°). Yeast which has been killed by boiling does not convert the disulfide into the mercaptan, but fermenting yeast does in view of the physiological importance of the disulfide group in cystine and glutathione, this observation is worthy of note. 

Since the alpha-ray impacts shattered only a minute proportion of the total number of atoms of boron, aluminum, or magnesium, the chemical identification of the products was extremely difficult. These indefatigable workers, however, accomplished even this. Although it would have been impossible to identify the products simply by ordinary chemical means, the Joliots were able to take advantage of the radioactive nature of the products formed. Since they had good reason to believe that the boron atom had captured a helion and ejected a neutron and that the new element was therefore probably an isotope of nitrogen, they heated some bombarded boron nitride with caustic soda and found that the liberated... 

If all the atoms in a particular substance have the same electron configuration (i.e., if they have the same number and arrangement of electrons), the substance is an element. An atom is the smallest particle of an element that can exist alone or in combination with particles of the same or a different element. Each atom of a particular element has the same number of protons in its nucleus. An element cannot be broken down by ordinary chemical means, such as burning, heating, or simply combining with other substances. 

A racemic form is 50 50 mixture of enantiomers. It is optically inactive. A racemic mixture of configurational isomers cannot be separated (resolved) by ordinary chemical means (distillation, crystallization, chromatography) unless the reagent is chiral. One way to separate a pair of enantiomers is to first convert them to diastereomers by reaction with a chiral reagent, then separate the diastereomers and regenerate the (now separate) enantiomers. 

As this process goes on, the electrons which remain in the zinc cause a negative charge to build up within the metal which makes it increasingly difficult for additional positive ions to leave the metallic phase. A similar buildup of positive charge in the liquid phase adds to this inhibition. Very soon, therefore, the process comes to a halt, resulting in a solution in which the concentration of Zn2+ is still too low (around 10-10 M) to be detected by ordinary chemical means. 

If a sample of matter cannot be broken down into simpler substances by ordinary chemical means, the sample is an element. [Ordinary chemical means includes any methods except nuclear reactions (Chapter 21).] An element has a definite set of properties. A compound is a chemical combination of elements that has its own set of properties and a definite composition. For example, pure water obtained from any natural source contains 88.8% oxygen and 11.2% hydrogen by mass. Compounds can be separated into their constituent elements only by chemical reaction. Elements and componnds are the two types of snbstances, often referred to as pnre snbstances. 

The nucleophile [Nu (or NuH)] may include H2O, ROH, OH, RO, RCOO, NO3, SCN", SeCN , CH3CN, NO2", N3", OCN", pyridine, halide ion, and CN the electrophile [ ] is most commonly H", but could be a carbocation or an alkoxonium ion. The case in which the electrophile is CO2 (the Kolbe reaction) is treated in Chapter 14 and will not be dealt with here. Anodic substitution reactions therefore allow for a net substitution by a nucleophile, a reaction not easily achieved by ordinary chemical means. Specifically, this makes possible the direct formation of a C-O or C-N bond by substitution of a C-H bond. This is of considerable synthetic interest. 

In the Middle Ages, many early chemists tried to change, or transmute, ordinary metals into gold. Although they made many discoveries that contributed to the development of modern chemistry, their attempts to transmute metals were doomed from the start. These early chemists did not realize that a transmutation, whereby one element changes into another, is a nuclear reaction. It changes the nucleus of an atom and therefore cannot be achieved by ordinary chemical means. 

Some steroid transformations, which are difficult to achieve by ordinary chemical means may also be accomplished readily by microbiological methods. Salicylic acid may be obtained in a 94% yield, on a weight for weight basis, by the action of Pseudomonas aeruginosa on naphthalene [69] (Eq. 16.25). 

Perhaps the greatest use of PAT at this time is to detect what are known as the priority pollutants. These originally included 128 industrial compounds that the Environmental Protection Agency considered as their first priority to monitor and regulate in our nations streams, lakes, and surface water. This list has since been expanded slightly. The tolerances set are very low, a safety factor of 1000 in most cases, and are usually not detectable by ordinary chemical means. However, the compounds can be concentrated by PAT and then are readily detectable. With computer assistance and a databank of standards for a mass spectrometer detector, the entire 128 compounds can be screened, detected, and quantitated at the ppb level and the report written in about 45 minutes. The technique is to choose a mass for each compound and set the mass spectrometer to monitor that mass. This eliminates most of the fragments and speeds up the identification and calculations. Table 33-2 is a list of the priority pollutants. Take a look at this list. If in later years you handle any of these compounds, be extra careful how you dispose of them. 

Virtually aU chemists in the late 1700s accepted the modem definition of an element as a substance that caimot he further broken down by ordinary chemical means. They also assumed that these elements combined to form compounds that have different physical and chemical properties than those of the elements that make them. What troubled them, however, was the understanding of just exactly how the different substances could combine with one another to form new ones, what we know as chemical reactions. Most historians date the foundation of modem chemistry to this time when scientists finally began to ascribe rules to how matter interacts. 

It is easy to remove two electrons (suppose we say two of the unpaired 3d electrons) to give the ferrous ion, a little more difficult to remove a third one, and impossible because of the large electrical field to remove the fourth electron by ordinary chemical means. Most of the ions of these metals are left with unpaired electrons, as is shown by their color and paramagnetism. 

As Table 21.1 indicates, the group 1 elements, the alkali metals, are relatively abundant. Some of their compounds have been known and used since prehistoric times. Yet these elements were not isolated in pure form until about 200 years ago. The compounds of the alkali metals are difficult to decompose by ordinary chemical means, so discovery of the elements had to await new scientific developments. Sodium (1807) and potassium (1807) were discovered through electrolysis. Lithium was discovered in 1817. Cesium (1860) and rubidium (1861) were identified as new elements through their emission spectra. Francium (1939) was isolated in the radioactive decay products of actinium. 

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