Water + questions

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WATER
Water is vital to living organisms: it is a metabolic reactant (used in many chemical reactions), a solvent, it transports
substances and helps with temperature control.
Hydrogen bonds are not just found in water. You will be expected to know how hydrogen bonds contribute to water's properties as
well as the stability of other molecules.
THE STRUCTURE OF WATER
Water is made up of two hydrogen atoms which are covalently bonded to one oxygen atom. COVALENT bonding is an
electron-sharing bond, and in this case sharing is not equal. The oxygen atom becomes more negatively charged, this is
written as delta minus. The hydrogen atom has a small positive charge; delta plus. This means that water molecules are
attracted to each other: a hydrogen bond. It is seen as a polar molecule (uneven charge distribution): it has a negative charge
on one side and a positive charge on the other.
In solid water-ice- hydrogen bonds hold the water molecules in a rigid lattice formation.
HIGH SPECIFIC HEAT CAPACITY
When you heat water, the temperature of the water rises. TEMPERATURE relates to the amount of kinetic energy the water
molecules have. As heat energy is added to the water, a lot of energy is required in order to break the hydrogen bonds
between the water molecules. This means that there is less energy to raise the temperature. Water therefore requires a lot of
heating in order to increase its temperature, it is said to have a HIGH SPECIFIC HEAT CAPACITY. 4.2kJ are necessary to increase
the temperature of 1kg of water by 1 degree.
The energy required to break hydrogen bonds between water molecules is known as their BOILING POINT.
Biological effect: this helps prevent changes in body temperature quickly and large temperature changes in the environment
have little effects on your body.
HIGH SPECIFIC LATENT HEAT
A great deal of heat energy is needed to make water change into water vapour. The heat needed to do this is called LATENT
HEAT. E.g. evaporation is a major cooling mechanism.

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Biological effect: This occurs in transpiration in plants and in sweating/panting in animals. Water is used as a coolant, it can be
used effectively as a small amount of water absorbs much thermal energy.
SOLVENT
Water is an excellent SOLVENT: the tiny charges (delta plus/minus) on its molecules attract other molecules that have charges
on them, in effect DISSOLVING them.
E.g. when an ionic compound (e.g. NaCl) dissolves in water, the sodium and chloride ions separate.
Biological effect: Transport in blood, xylem and the phloem.…read more

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