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 Water is essential for all life. Where there is no water at all, there is no life; therefore, water is one of the most important substances on earth.
Physical Properties
Water is ordorless, tasteless substance. It is a liquid at normal temperatures and pressures. It becomes a solid (ice) at temperatures below 0 degrees C (32 degrees F). It becomes an invisible gas at temperatures above 100 degrees C (212 degrees F).
Structure of Molecules
Water is a compound , a substance made up of two or more elements. Each molecule of water is composed of one oxygen atom bonded to two hydrogen atoms. Because of their bonding angles, hydrogen and oxygen combine to form a molecule that is similar in appearance to a narrow "Micky Mouse" head. The larger oxygen atom corresponds to the head and the small hydrogen atoms correspond to the ears.
Cohesion of Water
The structure of the molecule results in a polar or charged molecule. The hydrogen end of the molecule has a small positive charge and the oxygen end has a small negative charge. The polarity of the molecule causes water molecules to arrange themselves in an orderly fashion because each molecule is strongly attracted to the one closest to it. The attraction the molecules have for each other results in a powerful cohesion between them. Cohesion is the reason water "beads" on waxed surfaces. The plar nature of water molecules is a vital factor in water's ability to dissolve many other compounds. It also contributes to the ability of water to wet, or adhere to, some surfaces.
Water as a Solvent
In its pure form, water is an excellent solvent. It has the capability to dissolve many other substances. Water has been called the "universal solvent" because of its unique ability to dissolve so many other substances. Substances that dissolve easily in water are called hydrophilic or "water loving." In contrast, substances that do not mix well with water are called hydrophobic or "water fearing."
Importance of Solvent Qualities
The ability of water to dissolve many substances is one of its most important positive features. It allows dissolved gases, like oxygen and carbon dioxide, to be carried to and from living tissues. It allows chemical building blocks of living things to come together in solution so the necessary reations can take place. It carries away waste products, like ammonia and urea. Its ability to act as a solvent also allows us to use it as a cleaning product for our bodies, homes and housewares.
Negative Effects of Solvent Qualities
Water can leach nutrients from the soil, carrying them into eaterways and eventually to the sea. It can dissolve minerals like calcium, magnesium or other salts, which then make the water unfit for consumption or mate the water "hard." Hard water contains a fairly high concentration of dissolved minerals. The dissolved minerals interfere with the wetting action of soaps and detergents, making it moredifficult to produce a lather for washing. Minerals also react with cleaning products to produce a residue that is difficult to remove. Finally, minerals can accumulate as deposits in water heaters or other appliances, which shortens their life spans or makes them less efficient in operation. Water's ability to dissolve and carry materials can also contribute to the spread of pollutants that can be harmful to wildlife and people. In some areas this is the result of natural processes, but most cases of water pollution are the result of human error or lack of foresight in handling potentially harmful materials.
Activity for Kids
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