Why Does Ice Float on Water?

Why Does Ice Float on Water?

Have you ever wondered why ice is always floating on top of the water? You would think, water is a liquid and ice is a solid, since solids contract while cooling, their volumes increase, and the density would decrease. Thus, denser objects like ice would sink in water. But it doesn’t!

When the water is 35 degrees celsius, the water molecules are moving freely and running past each other. When the temperature drops to 4 degrees celsius, as mentioned in the particle theory, temperature affects the speed of the particles. The water molecules will move and run less. At this point, they are taking less space. If the temperature continues to drop, you might think that molecules will be closely packed together, which means decreasing volume and increasing density. But it is NOT what happens. Water behaves abnormally when it is cooled due to its unique molecular structure. Water has a special interaction between molecules, which is called a hydrogen bond. As we all know, water consists of two hydrogen atoms and one oxygen atom. The oxygen atom is slightly negative while the hydrogen atoms are slightly positive-charged. At normal temperatures, the bonds are constantly reforming and changing. When water is frozen, the molecules rearrange themselves into an open hexagonal form, which takes more space. Water Expands about 10% when It Freezes. This is saying, water expands on freezing and becomes less dense. So it can float on liquid water. This is called the anomalous expansion of water. This causes ice to have a higher volume. And thus, a lower density. 

Besides water, there are also other substances like plutonium, gallium, and acetic acid which behave similarly. 

There are many advantages that ice can float. An example is the icebergs that flow on rivers. They don’t sink in the river due to ice having a lower density. This is basically the same thing as polar ice caps, which float on the water and reflect 70% of the sunlight that otherwise would bake the earth. If ice sinks in water, we can’t skate nor fish in winter due to the ice being at the bottom of the oceans. And because ice is always the coldest layer in oceans, those deep-ocean animals would lose their habitats!

However, water expands during its solid form can bring disadvantages as well. In winter times, if pipes run outside of buildings and have a lack of protection, the water inside of the pipe freezes and the pipes might potentially collapse and burst. Because of this, many pipes are prone to this by constructing in metal, particularly copper pipes in the first place. Metal pipes are prone to this because it is relatively soft. Sometimes, pipes are built inside the exterior walls to prevent this as well. 

In conclusion, the main reason that ice has a lower density than water is because of hydrogen bonds, where water molecules transform into a form that takes more space. The world would change a lot if ice actually sank in water, for example, Antarctica would be gone, and we wouldn’t be able to skate and fish in winter! On the other hand, if water doesn’t expand in pipes during winter, you wouldn't need to worry about your pipes getting clotted!

Citations: 

Byrd-McDevitt, L. (n.d.). Why does ice float? | The Children’s Museum of Indianapolis. Www.Childrensmuseum.Org. Retrieved March 22, 2021, from https://www.childrensmuseum.org/blog/why-does-ice-float#:%7E:text=Believe%20it%20or%20not%2C%20ice,ice%20less%20dense%20than%20water%3F&text=So%20for%20water%2C%20the%20density,be%20less%20dense%20than%20water!  

TED-Ed. (2013, October 22). Why does ice float in water? - George Zaidan and Charles Morton [Video]. YouTube. https://www.youtube.com/watch?v=UukRgqzk-KE&feature=youtu.be

Don’t Memorise. (2020, September 23). Why does Ice Float on Water? | One Minute Bites | Don’t Memorise [Video]. YouTube. https://www.youtube.com/watch?v=oZOEFYogKn8&feature=youtu.be