Chemistry

Chemistry is the study of substances. Chemists investigate proper­ties of the substances that make up the universe and how these sub­stances behave under different conditions. They attempt to explain the behavior of a substance in terms of its structure and composition. Chemists also seek to understand chemical changes. These changes involve alterations in the chemical makeup of a substance. The com­bination of iron with oxygen from the air forming rust is a chemical change. Substances may also go through physical changes without altering their chemical makeup. Water changes physically but not chemically when it freezes.

Chemists have learned much about the chemical substances and processes that occur in the nature and have created many useful sub­stances that do not occur naturally, so they have greatly improved people's lives.

Chemistry studies many substances. Substances differ greatly in properties, structure, and composition. The methods chemists use and the questions they attempt to answer also differ greatly.

The most basic chemical substances are the chemical elements. They are the building blocks of all other substances. Each chemical element is made up of only one kind of atom. There are 91 elements known to exist on the Earth. Additional 20 elements have been pro­duced artificially. Electrical forces at the atomic level create chemical bonds that join two or more atoms together, forming molecules. Some molecules consist of atoms of a single element. When atoms of two or more different elements bond together, they form a chemical com­pound. Water is a compound of two hydrogen atoms and one oxygen atom. Compounds are formed or broken down by means of chemical reactions. All chemical reactions involve formation or destruction of chemical bonds.

Chemistry comprises the following sciences.

Analytical chemistry determines the identity and quantity of each element or compound present in a substance. Qualitative analysis is concerned with identifying the kinds of elements or compounds in a sample. Quantitative analysis indicates the amounts of the elements present. The techniques of analytical chemistry include the use of the spectroscope, mass spectrograph, X-ray tube, ultraviolet fluorescence, and radio isotopes.

Biochemistry is the study of the chemical composition of living matter and of the chemical processes that occur in living organisms. This field is particularly important in agriculture, biology, bacteriolo­gy, pharmacology, medicine, and dentistry.

Chemical engineering is a combination of chemistry and engineer­ing that develops or improves industrial processes for making com­mercial amounts of desirable chemicals that have been produced only in small quantities or in the laboratory.

Colloid chemistry is the study of the behavior of matter particles that are larger than ordinary molecules but smaller than objects that can be seen with the best optical microscope. Particles in this size range (10 to 2.000 A in diameter) have many unique properties. The tools used in this field include the ultracentrifuge, ultra microscope, and electron microscope.

Electrochemistry is the study of chemical reactions that are pro­duced by or produce an electric current. Also studied are the electrical conductivity of solutions and the phenomena that occur at electrodes application. Electrochemistry provides methods for chemical analysis and production of chemicals by electrical means.

Inorganic chemistry is the study of all elements and compounds that do not contain carbon. These include metals, halogens, and alkalies.

Nuclear chemistry is the study of radioactivity, atomic nucleus, and nuclear reactions, and the development of applications for radio­active isotopes in medicine and industry.

Organic chemistry is the study of carbon and its compounds. Car­bon compounds account for about 96 percent (about six and one-half million) of all known compounds. Among the carbon compounds studied by organic chemists are plant and animal tissues, petroleum, carbohydrates, proteins, plastics, and rubber.

Physical chemistry is the application of physical methods to the study of chemical problems. Included in this field are atomic and mo­lecular structure; theory of reaction rates; Mechanism of reactions; chemical equilibriums; energy changes in reactions; theories of solids, liquids, gases, plasmas, and solutions; electrochemistry; radioactivity.

Chemical Analysis

As you know, chemistry is the study of different kinds of matter, called substances, and the changes involved when one substance is transformed into another. Matter exists in three different states: solid, liquid and gaseous.

The most important characteristic of a substance is its uniformity of composition and the fact that all samples of a specific substance show the same properties. There are two kinds of properties: physical (color, taste, odor, touch, density, hardness, solubility and ability to conduct electricity and heat) and chemical. Chemical properties are the changes in composition undergone by a substance when it is sub­jected to various conditions. The various changes can be physical and chemical. The physical properties tend to be temporary. In a chemical change the composition of the substance is changed and new products are formed; these changes are permanent.

All pure substances can be divided according to their composition into two main classes: elements (metals a4d non-metals) and compounds.

Laboratory investigations of compounds follow two general tech­niques — analysis and synthesis. Analysis is breaking down (decompo­sing) the compound into its constituent elements. They in turn are then identified by qualitative analysis, and their relative weight or vol­ume is determined by quantitative analysis. The direct opposite of analysis is synthesis. Synthesis means building a compound from sim­pler substances or elements. For example, water is analyzed when an electric current is passed through it, decomposing it into hydrogen and oxygen; it is synthesized when hydrogen gas is burned in the presence of oxygen, forming water.

Nowadays the word assay can be applied to analysis in general, but in particular it means the analysis of pharmaceutical and official drugs. As saying by dry methods is dry-assay and by wet methods — wet-assay. An assay balance is also called an analytical balance.

There are such kinds of the qualitative analysis (detection of the kind of substances present): chemical by means of precipitation or wet method, thermal by means of flame tests and blowpipe analysis, opti­cal by means of spectroscopic and crystal structure, electrical by means of electrolysis and high frequency spectra, mechanical by means of microscope analysis and specific gravity, and biochemical by means of microorganisms — yeasts. The quantitative analysis (determination of the amount of substances present) can be mechanical by means of gravimetric methods (weighing the amount), volumetric methods (ti­trating the amount); thermal by means of combustion and combustion gases absorption; electrical by means of conductometry, mass spectra; and optical by means of colorimetry and fluoroscopy.

Grammar