GENERAL CHEMISTRY

Introduction

Chemistry is defined as the study of matter and its properties. Matter is defined as everything that has mass and occupies space.Although these definitions are acceptable, they do not explain why one needs to know chemistry. The answer to that query is that the world in which we live is a chemical world. Your own body is a complex chemical factory that uses chemical processes to change the food you eat and the air you breathe into bones, muscle, blood, and tissue and even into the energy that you use in your daily living. When illness prevents some part of these processes from functioning correctly, the doctor may prescribe as a medicine a chemical compound, either isolated from nature or prepared in a chemical laboratory by a chemist.

The world around us is also a vast chemical laboratory. The daily news is filled with reports of acid rain, toxic wastes, the risks associated with nuclear power plants, and the derailment of trains carrying substances such as vinyl chloride, sulfuric acid, and ammonia. Not all chemical news is of disasters. The daily news also carries stories (often in smaller headlines) of new drugs that cure old diseases; of fertilizers, insecticides, and herbicides designed by chemists to allow the farmers to feed our growing populations, and of other new products to make our lives more pleasant. The packages we buy at the grocery store list their contents, including what chemicals the package contains, such as preservatives, and the nutritional content in terms of vitamins, minerals, fats, carbohydrates, and proteins.

Everyday life is besieged with chemicals. In beginning the study of chemistry, it is unwise to start with topics as complex as the latest miracle drug. We will begin with the composition of matter and the different kinds of matter. We can then talk about the properties of the different types of matter and the changes that each can undergo. You will learn that each of these changes is accompanied by an energy change and learn the significance of these energy changes.

KINDS OF MATTER

Pure Substances

A pure substance consists of a single kind of matter. It always has the same composition and the same set of properties.For example, baking soda is a single kind of matter, known chemically as sodium hydrogen carbonate. A sample of pure baking soda, regardless of its source or size, will be a white solid containing 57.1% sodium, 1.2% hydrogen, 14.3% carbon, and 27.4% oxygen. The sample will dissolve in water. When heated to 270°C the sample will decompose, giving off carbon dioxide and water vapor and leaving a residue of sodium carbonate. Thus, by definition, baking soda is a pure substance because it has a constant composition and a unique set of properties, some of which we have listed. The properties we have described hold true for any sample of baking soda. These properties are the kinds in which we are interested.

A note about the term pure; in this text, the word pure means a single substance, not a mixture of substances. As used by the U.S. Food and Drug Administration (USFDA), the term pure means "fit for human consumption." Milk, whether whole, 2% fat, or skim, may be pure (fit for human consumption) by public health standards, but it is not pure in the chemical sense. Milk is a mixture of a great many substances, including water, butterfat, proteins, and sugars.

SYSTEMS OF MEASUREMENT

Measurements in the scientific world, and increasingly, in the nonscientific world are made in SI (Système International)units. The system was established in order to allow comparison of measurements made in one country with those made in another.

SI units and their relative values were adopted by an international association of scientists meeting in Paris in 1960. Table 2.1 lists the basic SI units and derived units. Notice that metric units are part of this system. The system still in common, nonscientific use in the United States is called the English system, even though England, like most other developed countries, now uses metric units. Anyone using units from both the English and SI systems needs to be aware of a few simple relationships between the two systems.

Two features of the SI system make it easy to use. First, it is a base-10 system; that is, the various units of a particular dimension vary by multiples of ten. Once a base unit is defined, units larger and smaller than the base unit are indicated by prefixes added to the name of the base unit. Table 2.2 (next page) lists some of these SI prefixes,along with the abbreviation for each and the numerical factor relating it to the base unit.