CHEMISTRY
1.1 IMPORTANCE OF BASIC CHEMISTRY
Chemistry plays a central role in science and is often intertwined with other branches of science. Principles of chemistry are applicable in diverse areas, such as weather patterns, functioning of brain and operation of a computer,gs, soa production in chemical industries, manufacturing fertilizers, alkalies, acids, salts, dyes, polymers, drups, detergents, metals, alloys, etc., including new material. Chemistry contributes in a big way to the national economy. It also plays an important role in meeting human needs for food, healthcare products and other material aimed at improving the quality of life. This is exemplified by the large-scale production of a variety of fertilizers, improved variety of pesticides and insecticides. Basic chemistry provides methods for the isolation of lifesaving drugs from natural sources and makes possible synthesis of such drugs. Some of these drugs are cis platin and taxol, which are effective in cancer therapy. The drug AZT (Azidothymidine) is used for helping AIDS patients. Basic chemistry also contributes to a large extent in the development and growth of a nation. With a better understanding of chemical principles it has now become possible to design and synthesize new material having specific magnetic, electric and optical properties. This has lead to the production of superconducting ceramics, conducting polymers, optical fibers, etc. Chemistry has helped in establishing industries which manufacture utility goods, like acids, alkalies, dyes, polymers metals, etc. These industries contribute in a big way to the economy of a nation and generate employment. In recent years, chemistry has helped in dealing with some of the pressing aspects of environmental degradation with a fair degree of success. Safer alternatives to environmentally hazardous refrigerants, like CFC's (chlorofluorocarbons), responsible for ozone depletion in the stratosphere, have been successfully synthesized. However, many big environmental problems continue to be matters of grave concern to the chemists. One such problem is the management of the Green House gases, like methane, carbon dioxide, etc. Understanding of biochemical processes, use of enzymes for large-scale production of chemicals and synthesis of new exotic material are some of the intellectual challenges for the future generation of chemists. A developing country, like India, needs talented and creative chemists for accepting such challenges. To be a good chemist and to accept such challenges, one needs to understand the basic concepts of chemistry, which begin with
the concept of matter. Let us start with the nature of matter.
1.2 NATURE OF MATTER
Anything which has mass and occupies space is called matter. Everything around us, for example, book, pen, pencil, water, air, all living beings, etc., are composed of matter. You know that they have mass and they occupy space.
1.2.1 States of Matter
matter can exist in three physical states viz. solid, liquid and gas. The constituent particles of matter in these three states can be represented as shown in Fig. 1.1.Particles are held very close to each other in solids in an orderly fashion and there is not much freedom of movement. In liquids, the particles are close to each other but they can move around. However, in gases, the particles are far apart as compared to those present in solid or liquid states and their movement is
easy and fast. Because of such arrangement of particles, different states of matter exhibit the following characteristics:
(I) Solids have definite volume and definite shape.
(II) Liquids have definite volume but do not have definite shape. They take the shape
of the container in which they are placed.
Fig. 1.1 Arrangement of particles in solid, liquid and gaseous state
(III) Gases have neither definite volume nor definite shape. They completely occupy the space in the container in which they are placed. These three states of matter are inter convertible by changing the conditions of temperature and pressure.
On heating, a solid usually changes to a liquid, and the liquid on further heating changes to gas (or vapor). In the reverse process, a gas on cooling liquefies to the liquid and the liquid on further cooling freezes to the solid.
1.2.2. Classification of Matter
At the macroscopic or bulk level, matter can be classified as mixture or pure substance. These can be further sub-divided as shown in Fig. 1.2. When all constituent particles of a substance are same in chemical nature, it is said to be a pure substance. A mixture contains many types of particles. A mixture contains particles of two or more pure substances which may be present in it in any ratio. Hence, their composition is variable. Pure substances forming mixture are called its components. Many of the substances present around you are mixtures. For example, sugar solution in water, air, tea, etc., are all mixtures. A mixture may be homogeneous or heterogeneous. In a homogeneous mixture,components completely mix with each other. This means particles of components of the mixture are uniformly distributed throughout
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Fig. 1.2 Classification of matter
the bulk of the mixture and its composition is uniform throughout. Sugar solution and air are the examples of homogeneous mixtures. In contrast to this, in a heterogeneous mixture, the composition is not uniform throughout and sometimes different components are visible. For example, mixtures of salt and sugar, grains and pulses along with some dirt (often stone pieces), are heterogeneous mixtures. You can think of many more examples of mixtures which you come across in the daily life. It is worthwhile to mention here that the components of a mixture can be separated by using physical methods, such as simple hand-picking, filtration, crystallization, distillation, etc. Pure substances have characteristics different from mixtures. Constituent particles of pure substances have fixed compositon ,copper, gold, water and glucose are some examples of pure substances. Glucose contains carbon, hydrogen and oxygen in a fixed ratio and its particles are of same composition. Hence, like all other pure substances, glucose has a fixed composition. Also, its constituents—carbon, hydrogen and oxygen—cannot be separated by simple physical methods.
Pure substances can further be classified into elements and compounds. Particles of an element consist of only one type of atoms. These particles may exist as atoms or molecules.
Sodium, copper, silver, hydrogen, oxygen, etc, are some examples of elements. Their
all atoms are of one type. However, the atoms of different elements are different in nature. Some elements, such as sodium or copper, contain atoms as their constituent particles, whereas, in some others, the constituent particles are molecules which are formed by two or more atoms. For example, hydrogen, nitrogen and oxygen gases consist of molecules, in which two atoms combine to give their respective molecules. This is illustrated in Fig.1.3
1.3 PROPERTIES OF MATTER AND THEIR MEASUREMENT
1.3.1 Physical and chemical properties
Every substance has unique or characteristic properties. These properties can be classified
into two categories — physical properties,such as colour, odour, melting point, boiling
point, density, etc., and chemical properties,like composition, combustibility, ractivity with
acids and bases, etc.Physical properties can be measured or observed without changing the identity or the composition of the substance. The measure mentor observation of chemical properties requires a chemical change to occur. Measurement of physical properties does not require occurrence a chemical change. The examples of chemical properties are characteristic reactions of different substances; these include acidity or basicity
1.3.2 Measurement of physical properties
Quantitative measurement of properties reacquired for scientific investigation. Many properties of matter, such as length, area,volume, etc., are quantitative in nature. Any quantitative observation or measurement is represented by a number followed by units in which it is measured. For example, length of a room can be represented as 6 m; here,6 is the number and m denotes meter, the unit in which the length is measured.Earlier, two different systems of measurement, i.e., the English System and the Metric System were being used indifferent parts of the world. The metric system,which originated in France in late eighteenth century, was more convenient as it was base don the decimal system. Late, need of a common standard system was felt by the scientific community. Such a system was established in 1960 and is discussed in detail below.
1.3.3 The International System of Units (SI)
The
International System of Units (in French Le
Systeme International d’Unités —abbreviated as
SI) was established by the 11th General
Conference on Weights and Measures (CGPM from Conference
Generale des Poids et Measures).
The CGPM is an inter-governmental treaty organization created by a diplomatic
treaty known as Metre Convention, which was signed in Paris in 1875.
The SI
system has seven base units and
they are listed in Table 1.1. These units pertain to the seven fundamental
scientific quantities. The other physical quantities, such as speed,
volume,
density, etc., can be derived from these quantities
The definitions of the SI base units are given in Table 1.2.
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