Explain the Characteristics of Water.
Water is a unique liquid, without which no life can survive. Water is a liquid at room temperature, with mp. 0°C, bp. 100°C, high dipole moment (1.84 x 10-3 esu), high dielectric constant (80), density (1.0), specific heat (1 Cal g-1 °C-1), high heat of evaporation (540 Cal g -1), surface tension (73 dynes cm-1 at 20°C) and viscosity (0.01 poise at 20°C). These abnormal properties of water are due to hydrogen bonding. The uniqueness of water is attributed to the following properties.
Water is regarded as a universal solvent. No other liquid can be compared to water as a solvent. Natural water is slightly acidic (pH 5.6) due to dissolved carbon dioxide, which gives carbonic acid (H2CO3). Therefore, it can dissolve a variety of compounds from simple salts to minerals including sodium chloride and calcium carbonate in limestone rock. Water also reacts with complex organic compounds including many amino acids found in the human body.
Water possesses highest heat of fusion and heat of evaporation, collectively known as latent heat, of all known liquid substances at ordinary temperature. The latent heat of water is responsible for moderating the temperature of the biosphere. It also plays a vital role in the evaporation of water and its condensation as rain and as dew (see hydro-logical cycle).
Compared with other common liquids, water has a high surface tension, a characteristic that is very important in many physical and biological processes involving movement of water through and into organisms.
Water is a poor thermal conductor as compared to other metals.
The high viscosity of water allows organisms to swim using simple
Water protects aquatic animals and plants from mechanical disturbances.
Among common compounds and molecules, water is the only one whose solid form (ice) is lighter than its liquid form; it expands by about 8 per cent when it freezes and becomes less dense. This is responsible for the Boating of ice on water. Can you imagine, if ice were heavier than water, it would sink to the bottom of water bodies; in such a situation, the biosphere would be entirely different than what it is today and life if existed could be greatly Freezing of water bodies from the bottom onward will result in complete freezing of water bodies resulting in the death of all life in water.
Being transparent to light, water allows photosynthetic organisms to live below the surface of water.
Water exerts pressure. Organisms living at the sea level experience a pressure of about 15 psi (∼1 atmosphere, which is equal to 360 mm mercury). With depth, the pressure increases at the ratio of about one atmosphere for every 10 meters of decent. The physical characteristics like solubility, ionic dissociation and surface tension are all influenced by the pressure.