HAPTER ONE
- INTRODUCTION
Water is a universal solvent, which consist of hydrogen and oxygen atoms. Chemically, it could be defined as a chemical substance with two atoms of hydrogen and one atom of oxygen in each of its molecules; hence the molecular formula is H2O. It is formed by the direct reaction of hydrogen with oxygen;
2H2 + O2 - 2H2O
Water is colourless, odourless and tasteless liquid in its pure form. It is an inorganic substance that occurs in three states; liquid gaseous and solid states1. Water covers 71% of the earth surface. On earth , it is found mostly in oceans and other large water bodies with 1.6% of water below ground in aquifers and 0.001% in the air as vapour clouds (formed from the solid and liquid water particles suspended in air), and precipitation2. Oceans hold 97% of surface water, glacier and polar ice cap 2.4% and other land surface water such as rivers, lakes and ponds 0.6%. A very small amount of the Earths water is contained within biological bodies and manufactured products. Water on earth moves continually through a cycle of evaporation, transpiration, precipitation and runoff, usually reaching the sea. Overland, evaporation and transpiration contributes to the precipitation. Clean and fresh drinking water is essential for human and other life forms. Access to safe drinking water has improved steadily and substantially over the last decades in almost every part of the world3, 4. There is a correlation between access to safe water and GDP, per capita5. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability6.
As water is heated from OOC, it contracts until 4oC is reached and then begins the expansion which is normally associated with increasing temperature. The viscosity of water decreases ten folds as the temperature is raised from OOC to 100 OC, and this also is associated with the decrease of ice like character in the water as the hydrogen bonds are disrupted by increasing thermal agitation. The electrical conductivity of water is at 1,000,000 times larger than that of most other non-metallic liquids at room temperature. The current in this case is carried by ions produced by the dissociation of water according to the reaction;
H2O = H+ + OH-
These products recombine completely to form water vapour, also undergoes most of the chemical reactions of liquid water and at very high concentration even shows some of the unusual solvents properties of liquid water. Above 3740C, water vapour may be compressed to any density without liquefying, and at a density as high as 0.4glcm3, it can dissolve appreciable quantities of salt7.
