The Physical Properties of Water

The important physical properties of water are summarized below:

  • Water has high specific heat capacity or simply specific heat (the amount of heat required to change the temperature of a 1-gram substance 1°C or 1°K at constant pressure). The specific heat of water is 1 cal/g°C (=4.184 J/g°C). The effect of heat production or loss and temperature changes in organisms are minimized which actually makes water a natural insulator. Therefore, life can survive in water through the seasons. Even though the air temperature changes wildly, the temperature of the lake does not fluctuate that much.

 

  • Density of water is higher than that of ice, since when water freezes it goes from a disordered state to a well-ordered rigid state. Ice formed on the surface of water and floats, thus insulates the water below it. That property gives opportunity to the aquatic ecosystem to survive under extremely low temperature conditions.

 

  • Water has high heat of fusion (heat required to melt a solid). The heat of fusion of ice is 79.97 cal/g (=334.83 J/g). That property protects living organisms against freezing.

 

  • Water has high heat of vaporization (heat required for evaporation). The heat vaporization of water is 540 cal/g (=2260 kJ/kg). An animal expends considerable heat to vaporize a small quantity of water in its body.

 

  • Polarity character of water makes it an excellent solvent. It can dissolve much more solutes and substances than any other liquid. The movement of water means the movement of valuable nutrients and minerals along with water.
  • When sodium chloride (also known as salt) is put in water, the negative ends of the water molecules are attracted to positively charged sodium ions, and positive ends of the water molecules are attracted to the negatively charged chloride ions. This causes the sodium chloride to dissociate in water.
  • Lipids are insoluble in water molecule. That’s the way that cellular membranes are formed. Phospholipids are composed of hydrophobic (water hating) tails with a hydrophilic (water loving) polar head. So, the tails want to get away from the water and this creates compartmentalization.

 

  • Pure water has a pH of 7.0 which is neutral. It is able to transfer protons back and forth by a process called autoionization. Most of the reactions in organisms depend on the components of H2O; hydronium and hydroxyl ions.

Autoprotolysis of water, resulting hydroxide and hydronium ions.

  • Hydrogen bonds hold the water molecules together that’s why water molecule is cohesive, that is highly sticky to each other. Water has high surface tension because of this sticky and polar nature. This property explains how plant leaves pull water molecules from root tissue against earth gravity.

 

  • Polar bonds also give molecules an adhesive property, or the ability to adhere other polar surfaces. So this is called adhesion and this is attraction between different substances for example between water and plant cell walls.

 

  • Pure water does not conduct electricity, unless any substance dissolves in it.

 

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