Water, the chemistry of life
If you thought water was a simple, innocent molecule, think again. Water is from far one of the most fascinating substance on our planet. Water remains one the major mysterises of the Universe. It supports life like no other substance does as chemical reactions in all plants and animals take place in water medium, releasing or consuming water in their metabolism. Life on Earth totally depends on water as living organisms are largely composed of water – about 70 to 90 percent by weight, and above 99 percent by absolute number of water molecules.
Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic life processes. Without water, these particular metabolic processes could not exist. Most of chemical reactions occur in the cell itself.
Water plays a central role in biological and chemical, especially acid-base, processes. Equally important to our comprehension of the structure and dynamics of water is understanding the role it plays as a solvent facilitating long-ranged charge transport of species such as ions, excess protons and hydroxide ions. The excess proton and hydroxide ion, both particularly important in acid-base chemistry and bio-molecular function, plays an important role in the metabolism of all organisms as reflected by the wide variety of chemical reactions in which they take part. Ions are cofactors of enzymes, catalyzing basic functions such as electron transport, redox reactions, and energy metabolism; they are essential for maintaining the osmotic pressure of cells too.
Water, the universal solvent
Water is often referred to as the universal, superb solvent. Mainly due to the marked polarity of the water molecule and its tendency to form hydrogen bonds with other molecules. All of the components in cells (proteins, DNA and polysaccharides) are dissolved in water deriving their structure and activity from their interactions with water. Water dissolves more substances in greater quantities than any other common liquid making water key important in chemical, physical and biological processes.
Basically, reduction means the addition of an election (e-), and its converse, oxidation means the removal of an electron. The addition of an electron, stores energy in the reduced compound. The removal of an electron, liberates energy from the oxidized compound. Whenever one substance is reduced, another is oxidized. In biological systems, removal or addition of an electron constitutes the most frequent mechanism of oxidation-reduction reactions, frequently called redox reactions.
Water is an acid and a base
Water can be both an acid and a base, depending on how you look at it. Water can even react with itself to form acid and bases. It happens in really small amounts; chemists have determined the concentration of H3O+ at 25°C as being very low: only a few molecules per billion will be dissociated. Dissociation of water forms an acid that increases the concentration of hydrogen ions (hydronium H3O+ also known as hydrated H+) and a base that increases the concentration of hydroxide ions (OH-). This can be amplified by using electrolysis process to drive an otherwise non-spontaneous chemical reaction.
The degree of acidity or alkalinity of a solution is measured in terms of a value known as pH, which is the negative logarithm of the concentration of hydrogen ions. Scientists have defined a pH scale which ranges from 0 on the acidic end to 14 on the alkaline end, a neutral solution being at pH 7. At pH 7 water contains equal concentrations of H+ and OH- ions. Substances with pH higher than 7 are alkaline as having a higher concentration of OH- than H+ and vice versa for acidic substance with pH lower than 7 containing a higher concentration of H+ than OH-. The pH scale is a log scale so a change of 1 pH units means a tenfold change in the concentration of hydrogen ions.
pH values of various substances
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