Icebergs can be massive, but many social media users may not be aware that they only see the tip of them above the water. Up to 90 per cent of an iceberg’s volume can be underwater. The reason behind this scientific phenomenon is that any solid substance whose density is lower than that of its liquid form can float in its liquid. The density of ice can decrease by about 9 per cent upon freezing. Consequently, some of the ice floats on the water’s surface.
The question arises: why is the density of ice less than that of water? The best way to visualise how water can have different densities is to examine its frozen form. Ice has a unique structure compared to liquid water. In ice, molecules align themselves in a regular lattice arrangement, rather than the more random arrangement in the liquid form. This lattice arrangement allows water molecules to be more spread out than in a liquid, resulting in ice being less dense than water. However, this explanation may not hold when comparing iceberg ice to the ice produced in household refrigerators. Ice placed in a glass of water typically remains submerged rather than floating on the surface.
Ice floats on water due to its lower density. However, a special type of ice can be denser than normal water. This ice is known as heavy ice and is 10.6 per cent denser than regular water because it is made from heavy water. Heavy water, or D2O, is water in which both hydrogen atoms have been replaced with deuterium, an isotope of hydrogen containing one proton and one neutron. Heavy water is indeed heavier than normal water, which naturally contains a small amount of heavy water molecules. Heavy-water ice will sink in regular water.
To measure the density of a block of ice, weigh it and then divide the weight by its volume.
Understanding the density differences between ice and water, as well as the unique properties of heavy water, provides insights into why icebergs float and how certain types of ice can be denser than water.
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