Question

The density of water is maximum at what temperature and what will happen if its density reduces on cooling?
A. Volume of water increases
B. Volume of water decreases
C. Volume of water first increase and then decrease
D. Temperature of water remains the same.

Answer 1

Water exhibits an unusual property on cooling from ${{4}^{\text{o}}}C$ to ${{0}^{\text{o}}}C$. It expands on cooling before turning into ice.

Complete Step by Step Answer:
The temperature of a substance is directly proportional to the volume. The volume is inversely proportional to the density of the substance. So, the temperature is inversely proportional to the density of the substance.
Usually with decrease in temperature, the liquids contract and their density increases. The density of water is maximum at ${{4}^{\text{o}}}C$. Water contract on cooling until the temperature ${{4}^{\text{o}}}C$, but thereafter it begins to expand till the temperature drops to ${{0}^{\text{o}}}C$, before turning into ice. The volume of ${{0}^{\text{o}}}C$ ice is greater than the volume of ${{0}^{\text{o}}}C$ water.

This phenomenon is known as anomalous expansion of water. Therefore, on cooling below ${{4}^{\text{o}}}C$, density of water reduces and its volume first increases till the temperature is ${{0}^{\text{o}}}C$ and then volume decreases to form ice at ${{0}^{\text{o}}}C$. So, option C is the correct answer.

Note: This anomalous expansion of water is useful for preservation of aquatic life in very cold temperatures. In cold countries, where temperature drops to ${{0}^{\text{o}}}C$, the lake surface starts cooling. At ${{4}^{\text{o}}}C$ temperature, the water has maximum density so the surface water descends to the bottom of the lake. On cooling further, the surface layer becomes ice. The density of ice is less than the density of water, so ice floats on water. However, below the ice the water at ${{4}^{\text{o}}}C$ sustains life.