Question

What does anomalous expansion of water mean?
(A). Water behaves like other liquid up to 4 degree centigrade. But below that temperature its density decreases till it is converted to ice.
(B). Water behaves like other liquid up to 4 degree centigrade. But below that temperature its density increases till it is converted to ice.
(C). Water behaves like other liquid up to 4 degree centigrade. But below that temperature its density remains constant till it is converted to ice.
(D). None of the above

Answer 1

- Hint: You should think about the irregular maximum density pattern for water to get the right option. Water shows maximum density at \[{{4}^{\circ }}\text{C}\]. Further cooling will affect the density. The bonds of water molecules will make lattice arrangements and prevent the motion of molecules. Even though some bonds are not rigid. So, it will increase the volume hence the density will decrease from \[{{4}^{\circ }}\text{C}\] onwards.

Complete step-by-step solution -

Normally liquids density will increase during cooling. Water is a special liquid and it will contract when cooled, down to a temperature of \[{{4}^{\circ }}\text{C}\]. Thereafter it begins to expand as it reaches \[{{0}^{\circ }}\text{C}\] and becomes ice. The maximum density of water is at \[{{4}^{\circ }}\text{C}\]. The density of the water decreases when you cool it from \[{{4}^{\circ }}\text{C}\] to \[{{0}^{\circ }}\text{C}\]. Molecules of water will form open crystal structures when it is in solid form. Hydrogen bonding between the oxygen and hydrogen atoms of different water molecules are the reason behind this property. At normal stages, intermolecular attraction keeps the water molecules. On cooling, these water molecules will lose energy and will start to squeeze together. This will cause the density increment. The lattice formation will prevent the movement of water molecules. This arrangement makes them stronger and denser. When \[{{4}^{\circ }}\text{C}\] attains no more squeezing is possible. Hence the option (A) is correct.

Additional information:
This is the reason behind the coldest layer formation on the top of the water bodies. Due to bad conductor properties of ice and water, they won’t allow the heat to pass the topmost layer. Hence, the groundwater will remain as water, and the topmost layer will become ice. Marine animals are preserved due to this phenomenon.

Note: This is an abnormal property and it is caused by the bonding between the oxygen and hydrogen atoms of two different molecules of water. Generally, liquids will expand on heating and contract on cooling. Due to the presence of hydrogen-oxygen bonds, water shows unusual properties. Since they need a large volume to occupy. Hence, expansion of water will happen. So other options are completely wrong in the case of water.