Physiology of Finfish and Shellfish (2+1)

1.2.4. Physical and chemical  properties

The major chemical and physical properties of water are:

• Water is a liquid at standard temperature and pressure. It is tasteless and odorless. The intrinsic color of water and ice is a very slight blue hue, although both appear colorless in small quantities.
• Water is transparent thus aquatic plants can live in water because sunlight can reach them.
• Water is a good solvent and is often referred to as the universal solvent. Substances that dissolve in water, e.g., salts, sugars, acids, alkalis, and some gases – especially oxygen, carbon dioxide (carbonation) are known as hydrophilic (water-loving) substances, while those that do not mix well with water (e.g., fats and oils), are known as hydrophobic (water-fearing) substances.
• All the major components in cells (proteins, DNA and polysaccharides ) are also dissolved in water.
• Pure water has a low electrical conductivity, but this increases significantly with the dissolution of a small amount of ionic material such as sodium chloride .
• The boiling point of water (and all other liquids) is dependent on the barometric pressure . For example, on the top of Mt. Everest water boils at 68 °C (154 °F), compared to 100 °C (212 °F) at sea level . Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.
• The maximum density of water occurs at 3.98 °C (39.16 °F). It has the anomalous property of becoming less dense, when it is cooled down to its solid form, ice. It expands to occupy 9% greater volume in this solid state, which accounts for the fact of ice floating on liquid water.
• Water is miscible with many liquids, such as ethanol , in all proportions, forming a single homogeneous liquid. As a gas, water vapor is completely miscible with air. On the other hand, water and most oils are immiscible usually forming layers according to increasing density from the top.
• Water can be split by electrolysis into hydrogen and oxygen.