Water - chemical structure,characteristics and properties

The earth is the only planet with water which supports life. The planet earth is also called the ‘blue planet’ due to the presence abundant water on its surface. Water occurs on its surface as liquid, ice and gas. Ocean covers 71% of the globe. Freshwater is less than 1%. Ice sheets cover polar region. Glaciers are found in higher mountains.
Water is the bloodstream of the biosphere. Water is one of the prime elements responsible for life on earth. Water sustains life and maintains ecological balance. Water is the essential component of global life support systems. The total amount of water on earth is 1.4 billion cubic kilometers, but only 41,000 km3 circulates in the hydrological cycle.Water is facing a crisis today. Water scarcity affects all social and economic sectors. There are concerns that water will increasingly be the cause of violence and even war. Water is recognized as one of the key limiting resources of this millennium.

Definition of water

Water is a binary compound that is colorless,tasteless, odorless liquid at room temperature.

Characteristics of Water

Water is a simple inorganic molecule. A water molecule has one oxygen and two hydrogen atoms.Water is a vital element for human life.The need for water rise along with population growth,urbanization and industrialization. Drought, floods and lack of fresh water may cause global     instability and conflict. Water is an essential element There is no life without water. There is no human activity that does not depend on water. Water is non-substitutable and there is no alternativefor water. Water is finite in quantity. All water comes from the rainfall. The amount of rainfall that falls on the continents is finite. Water is an unique substance. Water is neither created nor destroyed, it only moves from place to place and changes in quality. Water is precious. It costs money to extract, treat, process and distribute.
Unique uses of water - water is a unique solvent, a medium, a nourisher and a participant in biochemical reactions of living organisms. It is a prime element of industrial processes and a medium    for transportation.
Water is s visible and invisible natural substance. Water is the only natural substance that exists       in 3 physical states: solid, liquid and gas.

   Beneficial uses of water:

•         Domestic use-Drinking, Cooking, Bathing, washing.

•         Public use-  irrigation of parks,  Fire fighting, Filling pools

•         Agricultural use-Production of food grains, fruits and vegetables

•         Recreational use-Water sports

•         Industrial use used for cooling and creating steam

•         Environmental use-Habitat for aquatics &wildlife

   

•     The chemical structure of water 

A  water molecule has one oxygen atom and two hydrogen atoms. The two hydrogen atoms bound to one oxygen atom to form a ‘V’ shape at an angle of 105 degree. The length of the bond between the oxygen and the hydrogen is 95.84 pm (picometre). The chemical formula for water is H2O, meaning two hydrogen atoms covalently bonded to one oxygen atom.The water molecule has a tetrahedral structure with oxygen at its center. The two bonds with hydrogen are directed toward two corners of the tetrahedron. The unshared electrons occupy the remaining two corners.

Dielectric character-Oxygen is negatively charged with respect to the hydrogen in the water molecule. Although the water molecule as a whole is electrically neutral, the asymmetric distribution of electrons results in one side being positively charged with respect to the other.

Dipole character -Water has two different poles (dipole), like that of a magnet. The water molecule creates a region of positive charge and region of negative charge. When electrons are shared between oxygen and hydrogen, they are closer to the oxygen than the hydrogen. Therefore the oxygen has a greater negative charge due to the greater electron density. The hydrogen which is not very electronegative will have a greater positive charge due to the lack of electron density.

Water: a polar compound: The polar molecules have the property of attracting each other. As a result water molecules aggregate together. The polarity makes water a universal solvent. Water can dissolve salts, acids, sugars, as well as alkalies and gases. Most cell components including proteins, polysaccharides and DNA dissolve in water making it the basis of life.

Cohesion of water molecules -Cohesion is the force of attraction between molecules of the same substance. The hydrogen bonding between molecules makes water more 'sticky' leading to a higher degree of cohesion and adhesion. Cohesion due to hydrogen bonding contributes to the formation of waves and other water movements that occur in lakes.

Physical properties of water

Water has the highest boiling point, melting point, specific heat, heat of vaporization, latent heat of fusion, viscosity and tensile strength. Water scatters and absorbs light. Water absorbs light at the red end of the spectrum more easily than at the blue end. Water conducts sound waves. Water exerts pressure (i.e. Hydrostatic pressure= weight of the water). Water moves from the area of higher solute concentration to the area of lower solute concentration until equilibrium is reached.

    Chemical properties of water

Water is a source of hydrogen and oxygen for chemical reactions. Water is a highly reactive molecule which can form hydrogen bonds with other molecules. Water molecule each possesses a strongly nucleophilic oxygen atom that enables many of life’s reactions as well as ionizing to produce reactive hydrogen and hydroxide ions. Water combines with salts to form hydrates and reacts with metal oxides to form acids.

Global water cycle

Water evaporates from water bodies like seas, and oceans, lakes and rivers. Water vapor cools and condenses in the clouds. Water precipitates in the form of rain and snow which fall on the soil. Runoff and accumulation forms fresh water lakes, streams, ponds and groundwater.

Biological water cycle

This cycle refers to volume of water content in the living   organisms. Aquatic plants and freshwater animals absorb water from the surrounding medium by osmosis. Trees absorb water through roots from the moist soil. Land animals receive water by feeding and drinking. Plants loose water by transpiration through leaves. Animals loose water by sweating and elimination. After death, bacterial decomposition returns the water  to the environment.

Biological functions of water in humans

•         Water is one of the most essential elements to good health. It transports nutrients and oxygen to cells. It aids metabolic break down of proteins and carbohydrates. It helps in the  digestion and absorption of food. It protects body organs and tissues. It regulates body temperature. It facilitates the excretion of wastes. It lubricates joints and muscle tissues. It moistens tissues of mouth, eyes and nose. It serves as a natural air conditioning system.

Functions of soil water
 Soil water serves as a solvent and carrier of food nutrients for plant growth. It regulates soil temperature. It helps in chemical and biological activities of soil. Crop yield is proportional to the availability of water. Soil forming processes depend upon water.

Importance of water to plants

•      Water is the most abundant constituent of plant cells. Leaves consist of 55-85% water of their fresh weight. Water is fundamental to photosynthesis and respiration. Water maintains turgidity in plants which helps to stand erect.

Biological significance of water  

All life is aquatic.Life originates from water a billion years ago. Water forms a major constituent of life -The cells are filled with water. The tissues are bathed in watery extra cellular fluids. It is a medium for biochemical reactions. Three important types of reactions in water are precipitation, acid-base, and oxidation-reduction reactions.

•     Water protects and stabilizes plasma membranes  and  macromolecules. It  protects membrane proteins from de-naturation. It stabilizes lipid-protein-lipid  cell surface by hydrophobic interaction. Water is a habitat for animals - Permanent habitat for many species of fish (8,500 species).Temporary home for amphibians and reptiles (4,200 species).  High surface tension of water allows efficient blood clotting.

•     High electrical conductivity of water permits greater speed of impulse conduction.

Economic importance of water

Water is used in the direct production of agricultural and industrial goods. Water is used to produce energy-hydroelectric power. Water is used in the drilling, mining and processing of fossil fuels such as oil and coal. Water  is used to cool processors and material used in nuclear power plants.

Life–supporting functions of water:

•  Human consumption- (drinking and cooking)
•  Food production (irrigation)
•  Personal hygiene and Sanitation
•  Industrial production, energy generation economic development
•  Environmental protection

10-principles of water management

(Workshop on “Water and population dynamics” IUCN World Conservation congress in Montreal 1996)

• ·        Value Water
• ·        Use water sustainably
• ·        Develop suitable institutions to manage water
• ·        Collect and disseminate information
• ·        Maintain a social  and cultural perspective
• ·        Ensure equitable access to water
• ·        Use appropriate technology
• ·        Try to Solve causes, not symptoms -but accept practical solutions
• ·        Take an ecosystem approach
• ·        Work as multidisciplinary teams.