Question-3 : Water is denser as a liquid than as a solid. Can you explain why and how?

Question-3 :  Water is denser as a liquid than as a solid. Can you explain why and how?

Answer : 

Usually solids tend to have more density than their corresponding molten forms. Water is an exception - as it crystallizes by trapping air between the molecules as compared to the liquid forms. Density of water, under standard conditions tends to reach a maximum value at $4^{\circ }C$ (still liquid)

Hint: Density of a substance can be defined as the measure of its mass per unit volume. It is just the weight for a chosen amount or volume of the material.

Complete step by step answer:
We all know that as long as a substance is made of molecules it will have density and it can be given or defined as the mass divided by the volume of the substance.
The average density of an object equals its total mass divided by its total volume.

Now, from the definition of density we can say that an object that is made from a comparatively dense material such as iron will have less volume than an object equal in mass but which is made from some less dense substance such as water.

Generally, liquids are much denser than the gases because the molecules of liquids are packed relatively closer to each other than in the gases and due to the same reason the density of solids is more than the density of the liquids because the molecules of solid are more tightly packed. It is also known that the material or the substance with lower density tends to float upon the substance with the higher density. In general, the volume of the liquid is known to be more than the volume of the solid. This is due to the fact that the particles of the liquid are more free to move and thus results in more volume.

But, water in different forms tends to show an anomaly in this respect. The solid form of water, that is ice, floats on its liquid form, that is water itself. This is due to the fact that when water freezes to form ice, some empty spaces are created during this process.

Therefore, although being a solid, ice has a large amount of space between its molecules, which are larger in comparison with the spaces in water molecules. Thus, due to this the volume of the ice is more than that of water. Hence, water has more density than ice and therefore, ice floats on water.

Note: Water has maximum density when it is at 40C$4^{0}C$. After this the density of water decreases. And as we know, that water freezes at 00C$0^{0}C$, thus, it has less density than water.