Properties of Water: Anomalous Expansion of Water

Water is the most essential part of this planet. It covers almost 71% of the Earth’s surface of which 95% water is salty that is undrinkable. Only 2% of the water present is fresh and drinkable. Water has a wide range of use. It is used for the survival of human beings, flora, and fauna. The importance of water can be estimated from the fact that 75% of the human brain is made up of water. Water is not only used for recreations and day-to-day activities but is also used in industries, agriculture, etc. The chemical composition of water is H2O which means one molecule of water is made of one oxygen atom and two hydrogen atoms held together by a strong covalent bond. Water is lightest in gas form whereas as a liquid it is much heavier than its solid form. It is a good conductor of electricity and has different properties. Water is colourless, odourless, and tasteless. Apart from these, there are various other properties that make water unique. Water is found everywhere in different forms. At poles, it is found in the form of ice whereas at other places it is found in the form of liquid. 


Properties of Water:

Amphoteric Nature: It can behave as both - acid and base.

Hydrolysis: Water has a very high dielectric constant.

Viscosity: It has high viscosity due to the intermolecular force of attraction.

Redox Reactions: Water is a great source to obtain dihydrogen.

Hydrates Formation: It is defined as the attachment of water molecules with any compound. There are various types of hydrates. They are:

  • Co-ordination hydrates

  • Interstitial hydrates

  • Hydrogen bond hydrates

 

There are Two Properties of Water Due to the Hydrogen Bond. They are:

Cohesion: Molecules are close to each other because of the collective action of the hydrogen bond. Cohesive forces are responsible for the phenomenon of surface tension between water molecules.

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Adhesion: It is the bonding of water molecules with other molecules. This characteristic causes capillary action i.e., the ability of water to flow against gravity in a narrow space.

  • High specific heat

  • The high heat of vaporization

  • The lower density of ice

 

Anomalous Expansion of Water:

Water shows the un-natural behaviour which makes it unique. Between a certain range of temperatures, it shows anomalous expansion of water which has many applications. This helps in the survival of marine life, this is one of the major importance of this behaviour of water, and there are many applications which are discussed.

Generally, on heating water it expands and on cooling it contracts. But in case of liquid, it shows unusual behaviour from to . Between this range, water doesn't follow the Law of Contraction and Expansion i.e., as you cool down the water its density increases till and reaches its maximum range. If one tries to cool it below to make ice at the temperature of the water decreases as normal but its density also decreases instead of increasing. This leads to the expansion of ice and not contraction.

In other words, at water attains its maximum density and minimum volume (from the equation) i.e., the volume is inversely proportional to density. Below 4 degree Celsius the density will gradually decrease as the temperature decreases and reaches leading to increase in volume.

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From the below graph it can be seen.

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Hence, it is clear from the graph that density increases as temperature rises from to 4 degree Celsius and then density decreases after.

 

Application:

This property of anomalous expansion of water has many applications

 

Aquatic Life: This unique property of water helps the aquatic life to survive. As the temperature reaches it reaches its maximum density and sinks to the bottom of a lake or pond or any water bodies. So, as the temperature starts decreasing water expands. Therefore, the volume increases and density decreases due to which water starts floating on top. With a further drop in temperature water on top forms ice and become a bad conductor of heat. This stops the heat from escaping the water body and helps the aquatic life to survive. Hence, aquatic life can survive even when the temperature reaches or falls below.

 

Bottle Burst: If you put a full-filled water bottle in the refrigerator and its temperature is below . Then according to the anomalous behaviour of water, the water inside the bottle will expand. Therefore, due to no space in the bottle for the expansion of water molecules, water will exert force on the walls of the bottle and burst.

 

Soft Drinks Bottle: Soft drink bottles are kept in freezers. So, as the temperature drops below the drink inside the bottle starts expanding. So to prevent the molecules from exerting force on the wall and burst, there is a little space left inside the bottle.

In cold countries, water pipes expand due to anomalous behaviour of water and hence the water exerts a large amount of force on the pipe wall and it bursts.

Rocks break during winter because as the temperature decreases below water inside the rocks start expanding and hence exert a large amount of force on the rocks and results in the breaking of rocks.

 

Why Does it Happen?

The water molecule is made up of one oxygen and two hydrogen molecules. The water molecules are held together because of the intermolecular force of attraction between them at normal temperature. The molecules of water in liquid form are always unstable moving zig-zag inside the container, constantly rearranging themselves.

On cooling the water, zig-zag motion decreases as the molecules lose their energy. On freezing, the water molecules start squeezing and at water density reaches its maximum density. This is caused by the hydrogen bonding between the oxygen atoms that are negatively charged and the hydrogen atom that is positively charged, from two different molecules of water. 

The rise in temperature above will cause the ice to form water not because of the O-O bond but due to H-O bond attraction. The lattice structure of ice prevents the movement of water molecules. But since the H-O bond is not as strong as the O-O bond it will expand and hence occupies more space. This can be understood with an example: Suppose 5 people are seating on a seat with their hands folded but as they start stretching their hands, there is a possibility that the corner one may fall. So, the same goes in case of water also, as the H-O bond overtakes, it requires more space.

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