Question

True or False.
Water contracts on freezing.

Answer 1

Hint: When water freezes, formation of ice takes place. It changes from liquid to solid state. Water crystallizes into hexagonal structure. It begins to take a more stable and definite shape.

Complete step by step answer:
The normal behavior observed in any substance is that they usually expand when heated as their density decreases and contracts on cooling as their density is maximum. But water is an exception. Water has a special property which is known as anomalous expansion of water. Because of this property, water when it freezes, its density becomes maximum value upto \[{{4}^{{}^\circ }}C\]. After that when the temperature of water changes from \[{{4}^{{}^\circ }}C\text{ to }{{\text{0}}^{{}^\circ }}\text{C}\] the density of water decreases and hence water starts to expand. When water freezes, its molecules form a hexagonal structure and therefore its size expands.
Water molecules contain two hydrogen atoms and one oxygen atom. Water molecules are held together by intermolecular force of attraction. In liquid state water molecules can freely move around the container. They do not have any specific arrangement. There is a force of attraction between the hydrogen atom of one water molecule and oxygen atom of another water molecule. Although this force is not that strong compared to O-O attraction.
When the water begins to freeze into ice, the water molecules are held by H-O bonds. This bond is not as tight as an O-O bond. As the H-O force of attraction is present in ice, its size expands.

Therefore, the statement saying water contracts on freezing is a false statement.

Additional information:
There are other substances which can expand upon freezing. They are:
- Bismuth
- Gallium
- Acetic acid

Note: - The anomalous expansion property of water helps to preserve the lives of aquatic plants and animals in cold climate.
- The way this property protects marine life is that during cooling of water, it becomes very dense at \[{{4}^{{}^\circ }}C\]. Due to maximum density the water at the top layer reaches the bottom and the lightest water at the bottom of the water body comes to the top. This lightest layer at the top is the first one to get frozen. After the top layer is completely frozen, it will not allow the cold of the winter to reach the bottom. This is because water and ice are insulators. Hence protecting the aquatic lives.