Chemistry

The Chemistry of Water



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Water is a molecule made up of two hydrogen atoms and an oxygen atom. This is a molecule that is hugely important in both biology and chemistry. Chemically speaking water has a permanent dipole as oxygen is more electronegative than hydrogen and so attracts the electron pair from the covalent bond more strongly, this means that the oxygen atom has a slight negative charge and the hydrogen atoms have a slight positive charge.

Water has a very high boiling point for a molecule of its size even considering the dipolar interactions between the negative oxygen and positive hydrogen. This is explained by hydrogen bonding that occurs as the hydrogen atom is so small that it fit especially close to the oxygen atom and hence there is a stronger intermolecular force of attraction. This force of attraction is responsible for many of water's unique properties such as its very high boiling point. Water is less dense in its solid form and so ice floats on water, which is very unusual for a molecule: this is because the hydrogen bonds that are fully formed in ice have a set length and so since in the liquid form the average distance between molecules is reduced due to the kinetic energy of the molecules the solid form of water is less dense and so floats. Surface tension is also mainly due to the way that water has strong interactions between molecules. This is known as cohesion and is very important in plants as it allows water to be drawn up the stem in a long column.

Chemically speaking water is found in a whole host of chemical equations the most obvious is the combustion of many substances such as hydrogen gas and hydrocarbons.

Water also appears in many redox reactions in order to balance the hydrogen ions that are in turn used to balance the electrons gained or lost. Water is a very important solvent for many, if not most chemical reactions. For example water is the best solvent for solvating both anions and cations due to the polar nature of molecules and so various interactions can occur that would not occur in another solvent.

Water is also very important in acid/base reactions as it is amphoteric, acting as an acid and base as a water molecule may either accept or lose an electron comfortably.

Water is perhaps so important that it could be said to be a solvent that is absolutely crucial for life to exist as it occupies upto 80% of living tissue and no other solvent has been found that is able to solvate so many different substances.

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