Question

Why does ice float on water?

Answer 1

Water in its solid state is called ice. Understand the way water molecules are arranged in ice. Generally, solid form of a matter is denser than its liquid form. The case with ice is an exception. Liquid water is slightly denser than ice.

Complete step by step solution:
Density is defined as the mass per unit volume of a substance. As the mass of a substance increases, its density increases and as the volume of a substance increases, its density decreases. When a liquid is cooled, molecules are brought together which need to be accommodated in a smaller area. This increases the density of the substance and thereby most of the solids have greater density than liquids.
However, when water is cooled and ice is formed, a large number of empty spaces is left between the particles of ice. This is because when the water is frozen, the molecules are not able to form as many hydrogen bonds as compared to liquid water. Thus, the molecules of ice are not as close compared to those of liquid water. Ice formed has a cage-like structure. The spaces formed are larger as compared to the spaces present between the particles of water.
Hence, the density of ice is less than that of liquid water and thus ice floats on water.

Note: Remember that water is most dense at a temperature of ${4^0}C$. At any temperature above or below this temperature, water gets less dense. So, ice is less dense than liquid water. The instrument to measure the density of a liquid is called a hydrometer. In liquid water, each molecule of hydrogen is bonded to approximately 3.4 other water molecules. In ice, each molecule of hydrogen is bonded to 4 other water molecules.