Question

When ice melts, its volume:
A.)decreases
B.)increases
C.)remains same
D.)may increase or decrease

Answer 1

Hint: Recall the anomalous expansion of water i.e., Normally, liquids contract on cooling & the density increases. However, water is special. It contracts when cooled, down to a temperature of 4°C but thereafter begins to expand as it reaches 0°C and turns into ice.

Complete step by step answer:

When water is heated from 0°C to 4°C it contracts continuously instead of expanding. Conversely it expands when cooled down from 4°C to 0°C This expansion of water from 4°C to 0°C is called anomalous expansion. This is known as anomalous expansion of water.

When heated from 4°C to 100°C its expansion is normal like the expansion of other liquids. Since water contracts when heated from 0°C to 4°C and expands from 4°C to 100°C, its volume is least and the density is maximum at 4°C.

Therefore, when the ice melts (heated from 0°C to 4°C) it contracts and decreases its density as a result of which volume decreases.

Hence, the correct option is A, i.e., decreases.
Additional Information:

Reason for anomalous expansion: The water molecule, consisting of two atoms of hydrogen and one of oxygen forms the structure. The oxygen atom side of the molecule is slightly negative while the hydrogen atoms side has a slight positive charge. This makes the water molecules drawn towards each other forming hydrogen bonds.
Upon freezing, the molecules set themselves in an arrangement that is very open in nature and contains more space than the water in the liquid state. Hence, water is said to expand on freezing and becomes less dense. On the other hand, it contracts on defrosting, much unlike most other liquids.

Note: Students should understand the anomalous expansion of water with reason. So that they do not confuse that the density decreases on increasing of temperature like other liquids. Students should keep in mind that water contracts, from 0°C to 4°C and thereafter expands from 4°C to 100°C.