Effects of Impurities on the Heat Absorption and Retention Capacity of Freshwater
CHAPTER ONE
PREAMBLE OF THE STUDY
Water is a transparent fluid which forms the world’s streams, rivers, lakes, rain, and oceans. As a chemical compound, a single water molecule contains one atom of oxygen, and two atoms of hydrogen connected by covalent bonds.
Water covers 71% of the total Earth’s surface.96.5% of earth’s water is found in seas and oceans, 1.7% in groundwater, 1.7% in glaciers and ice caps of Antarctica and Greenland, a small fraction of water can be found in other large water bodies, and 0.001% in the air as vapor, clouds (formed of ice and liquid water suspended in air), and precipitation .Only 2.5% of the Earth’s water is freshwater, and 98.8% of that water is ice (excepting ice in clouds) and groundwater. Only less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere (Gleick, P.H 1993).
Many substances dissolve in water and it is commonly referred to as the universal solvent. For this cause, water in nature and in use is rarely pure and some properties may vary from those of the pure substance. However, there are also many compounds that are essentially, if not completely insoluble in water. Pure Water has a boiling and melting point of 100⁰C and 0⁰C respectively. Water is the only common substance found naturally in all three common states of matter and it is essential for all life on Earth. Water makes up 55-78% of the human body, so its importance cannot be overemphasized.
CHAPTER TWO
LITERATURE REVIEW
CONCEPTUAL FRAMEWORK
Electrical Conductivity of Water
Most natural waters contain dissolved ions (atoms or molecules possessing a charge) derived from the water’s interaction with soil, bedrock, atmosphere, and biosphere. As a result of these ions, water is able to conduct electricity much better than it otherwise can: for example, sea water with its dissolved salts can conduct electricity about 100 times more readily than distilled water. In any case, the ability of water to conduct electricity is the reason for the warning labels that appear on most electrical appliances warning consumers not to operate them near water.
The electrical conductivity (or specific conductance) of water depends on the concentration and charge of the dissolved ions (Weast, Robert C. 2000). Because of this relationship, conductivity often is used as an indicator of the total dissolved solids (TDS) in the water. The TDS is an important chemical property of water that provides information regarding the water’s history of “evolution” (for instance, its movement through underground aquifers). Conductivity is only an estimate of TDS, however, because a given value of conductivity can be produced by several different combinations of ion concentration and charge.
Dissolving Capacity of Water
Water molecules also can be attracted to surfaces of minerals in soils and rocks. This attraction allows dissolving (dissolution) and other chemical reactions to occur so readily that water often is called the “universal solvent.” Because water can dissolve and carry a wide range of chemicals, minerals, and nutrients, it plays an essential role in almost all biological and geochemical processes.
PH of Water
One important chemical property of natural water that affects its ability to dissolve minerals and influence chemical reactions is its pH. The pH, which indicates the acidity of water, measures the abundance of positively charged hydrogen ions (H +), and is defined numerically as the negative logarithm of the concentration of H + ions. Because pH is measured on a logarithmic scale, the concentration of H+ ions is ten times greater in water with a pH of 5 than water with a pH of 6, for example.
Water with a pH greater than 0 and less than 7 is termed acidic; a pH equaling 7 is neutral at temperatures at the Earth’s surface; and a pH between 7 and 14 is termed alkaline (or basic). Distilled water is considered neutral, and has a pH of 7. Natural waters also can be neutral, but more often are either slightly acidic or slightly basic.
Water in some volcanic caldera lakes can be very acidic, with pH values sometimes less than 1. If a wristwatch were dropped into water this acidic, the watch would be damaged beyond recognition within minutes. Rain in unpolluted areas has a pH of about 5.6 due to the dissolution of carbon dioxide in the atmosphere. This slightly acidic nature enhances rain-water’s dissolving power. In some locations, rainwater’s acidity is greatly increased (the pH is lowered) by the absorption of certain atmospheric pollutants, causing what is called acid rain. Rainwater is neutralized by chemical reactions with minerals in soils and rocks so that the pH of most streams and lakes is between about 6.5 and 8.5. Aquatic organisms often are very sensitive to the pH of water. Below a pH of about 5, most fish will die.
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