Question

At what temperature the density of water is maximum? State its value.

Answer 1

Hint: Water is a liquid with exceptional properties compared with other liquids. The hydrogen bonds in the liquids decide the liquids thermodynamic and dynamic behaviour. The enrichment of hydrogen bonds makes water as unique. When we are reducing the temperature, we can increase the density of the water. But after a specific value, the water decreases the density. This property is known as the anomalous expansion of water.

Complete step by step solution:
Normally liquids density decreases with increasing temperature due to the enhanced movement of molecules. Water is a special liquid. However, it will contract when cooled like other liquids, down to a temperature of \[\text{4 }\!\!{}^\circ\!\!\text{ C}\]. Thereafter it begins to expand as it reaches \[\text{0 }\!\!{}^\circ\!\!\text{ C}\] and water becomes ice. So, the maximum density of water is \[1000\text{ kg }{{\text{m}}^{-3}}\] and it will occur at \[\text{4 }\!\!{}^\circ\!\!\text{ C}\]. Since the density is in an inverse relationship with the volume. The volume will increase with the expansion.
As we know, the density of ice is lower compared to the water. Compared to other materials, water possesses more density, not in the solid form. That’s why ice can float in the water. This anomalous property arises due to the abnormal property of water in which the water expands instead of contracting when the temperature goes down from \[\text{4 }\!\!{}^\circ\!\!\text{ C}\] to \[\text{0 }\!\!{}^\circ\!\!\text{ C}\]. At this time, the water is less dense. If we are reducing temperature again, the water will become ice.
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 a normal stage, 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 \[\text{4 }\!\!{}^\circ\!\!\text{ C}\] attains no more squeezing is possible. That’s why the density decreases if we are reducing temperature again. At this time, the O-H bond will start to expand slightly. This will cause the expansion of water.

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 hydrogen bonding between the oxygen and hydrogen atoms of two different molecules of water. The contraction makes the bond formation between hydrogen and oxygen atoms of different molecules. Once it reaches the extreme level, it will start to expand slightly. As we know, no one can stand for a long time in a small tunnel. Like this, the molecules also start to expand. At this time density decreases. In our case, this decrement of density will occur from \[\text{4 }\!\!{}^\circ\!\!\text{ C}\] to \[\text{0 }\!\!{}^\circ\!\!\text{ C}\]. At \[\text{4 }\!\!{}^\circ\!\!\text{ C}\] the density will be maximum.