WATER PROPERTIES

Water has a number of important properties below are due to the hydrogen bonds in water :

Water as Universal SolventHigh Specific Heat Capacity of WaterHigh Latent Heat of Vaporisation of WaterLow ViscosityHigh Cohesion and Adhesion of WaterLower Density in Solid StateThe Ionisation of Water

NOOR ASYIKIN BT KAMARAZAMAN D20091034860

SITI SARAH BT MOHD SAIFUDDIND20091034843

NURUL HUSNA BT ALIASD20091034858

SYARIFAH ROQAIYAH BT MUD PUADD20091034851

ZAINAB FASIHAH BT MUHAMAD SUKARDID20091034842

SITI SHAHIDA BT MOHD AZIRID20091034836

1) Water as Universal Solvent

good solvent due to its polarity.Polar water molecules attract each other as well as ions and other polar molecules.Because of this attraction, water can dissolve many ionic compounds.Polar molecules such as salt,sugars and amino acids are hydrophilic while non-polar molecules such as lipids are hydrophobic.This property allow only a certain molecules to dissolve in water while preventing others from entering the cell.

2) High Specific Heat Capacity of Water

Specific heat of a substance is the amount of heat that must be absorbed or lost by 1 gram of that substance in order to change its temperature by 1°C.The high specific heat of water is due to the high energy required to break the hydrogen bonds that hold the liquid together.As such, a large input of thermal energy is required to break these bonds before the individual molecules can move freely.

This property allows water to absorb or lose large amounts of heat without undergoing correspondingly large changes in temperatures. Thus:

It enables organisms with a high content of water to maintain a relatively constant internal temperatures. It allows lakes and oceans to maintain a relatively constant temperatures.

3) High Latent Heat of Vaporisation of Water

Latent heat of vapourisation is the energy required to break its hydrogen bonds to changes its state from liquid to water.Water has a relatively high latent heat of vaporisation ( 586 calories/ g) when compared with other substances.Evaporation of water from a surface causes cooling of that surface as heat is removed.This is used as a cooling mechanism in animals

( sweating and panting ) and plants ( transpiration).As water evaporates it extracts heat from around it, thus cooling the organism.

4) Low Viscocity

This property enable water to act as a lubricant.Water is the major component of plasma, mucus and other lubricating fluids.Lubrication is necessary when the internal organs come in contact and slide over one another.It enables blood to function well as an efficient medium of transport for gases and nutrients throughout the body.

5) High Cohesion and Adhesion of Water

The polar nature of water and the formation hydrogen bonds contribute to cohesion in water.Cohesion is the force that attracts water molecules together.The surface tension on the surface of water is the product of the cohesive forces generated by hydrogen bonding between adjacent water molecules and to the molecules below them.Adhesion is referred to as the force of attraction between unlike molecules.

Water is adhesive to any substance with which it can form hydrogen bonds.Both cohesion and adhesive forces are responsible for capillary action. It enable water molecules to rise in fine capillary tubes.With capillary action, minerals dissolved in water are taken up by the roots and are transported up the stem to the leaves.

6) Lower density in solid state

The movement of the molecules slows down and they crowd closer to one another as the temperature of water decreases. As the temperature of water approaches 0°C, the molecules form more hydrogen bonds with each other. They lose kinetic energy.At 0°C or below, water freezes and changes into a solid state. In this state, each molecule is hydrogen bonded firmly to four other water molecules.

PROPERTIES OF WATER AND ITS ROLE

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