Why Does Oil Float On Water? Curious Chemistry Question Explained!

Martha Martins
Oct 12, 2023 By Martha Martins
Originally Published on Oct 29, 2021
Oil floating on water in a glass.

If oil spills on the ground, you need soap for cleaning because water alone can't remove oil.

This happens because the water never mixes with oil. Ever thought about why this happens, like why oil and water don't dissolve in each other and always stay separate?

Well, this is a very simple matter. The main difference between oil and water is that water is a polar solvent while oil is non-polar in nature. Non-polar substances don't mix well with polar substances.

This is why oil and water don't mix. But there is more to it. Then why does oil float and not sink?

Well, oil is lighter than water and that's why it floats on the water surface. In the article, there is more information on why oil and water don't mix. Read on to find out!

If you like reading such fun facts then you will also enjoy our articles on who invented socks and who invented cotton candy.

Why does oil float on water?

The easiest explanation for this question would be that oil is hydrophobic in nature and is less dense, so it doesn't mix or dissolve in water and floats on the surface.

Explaining to a kid with proper science with chemical equations for why oil floats on water won't be perfect. Rather it should be simplified.

For answering why water, oil doesn't mix, liquids like oils are hydrophobic in nature (hydrophobic is the opposite to hydrophilic). Hydrophobic are those substances that don't mix in water and stay separated. And to answer why oil floats on water, liquids like oil are less dense than water.

And because they don't dissolve in water, they keep floating on the surface because of their less density. Because of this hydrophobic property, oil keeps floating on water.

When oil spills in the ocean why does the oil float on the water?

We have heard about oil spill cases in the ocean several times. But why the liquid doesn't sink, dissolve or get mixed with the ocean water and always come to the surface! Ever thought about this?

Well, oil and water never mix with each other. Water has a higher density and is heavier than oil and always stays under the oil layer.

Actually, the difference between oil and water molecule is that oil molecules are non-polar in nature while water molecule is polar in nature. According to chemical science, non-polar molecules do not dissolve in polar solvents and actually repel each other. This property can be given the credit for oil and water never mixing with each other.

What liquid is more dense than water?

Glycerol is one of the liquids that are denser than water. Water is a polar solvent. Density is mass per unit volume.

Here mass is directly proportional to density while volume is inversely proportional. This means the bigger the mass, the bigger the density while the bigger the volume, the smaller the density. So we can say if two objects have the same volume, the object with greater mass will have higher density.

Having said that, glycerol is one of the liquids that are heavier than water, there are several other liquids that are heavier than water, unlike oil. One of those other liquids is corn syrup.

Corn syrup is heavier than water and if you add it to water, it will just simply sink. Out of all of these, mercury is considered the heaviest liquid with a density of 450.6 oz/qt (13.5 g/ml).

If the object added to water is heavier, it will sink, and if it is lighter, it will start floating. Oil and water never get along and oil keeps floating on the surface of the water because of its lower density.

Is water the heaviest liquid?

The simple answer to this question is 'no'. Water is not the heaviest liquid.

There are several other liquids present that are heavier than water according to science. The density of water is around 1 g/ml. But the most insane thing about water is that its density changes with temperature and the highest density is at around 39.2 F (4 C).

Water is not the heaviest liquid, rather the heaviest liquid is mercury. There are other liquids also there which are heavier than water.

Syrups and glycerol are known to be heavier than water. If you add any of these to water, you will notice that it will sink to the bottom of the glass. Well, water might not be the heaviest liquid but it is heavier than other liquids like oil and alcohol.

These liquids float on the surface and don't mix well. Oil and water repel each other and never dissolve in each other. There is a record on whether water is the thinnest liquid or not but it is surely thin in nature.

There is a fun fact on wax. Wax sinks in kerosene oil but floats on water!

Here at Kidadl, we have carefully created lots of interesting family-friendly facts for everyone to enjoy! If you liked our suggestions for why does oil float on water?, then why not take a look at what is a queen, or what is nougat!

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Written by Martha Martins

Bachelor of Arts specializing in Linguistics

Martha Martins picture

Martha MartinsBachelor of Arts specializing in Linguistics

Martha is a full-time creative writer, content strategist, and aspiring screenwriter who communicates complex thoughts and ideas effectively. She has completed her Bachelor's in Linguistics from Nasarawa State University. As an enthusiast of public relations and communication, Martha is well-prepared to substantially impact your organization as your next content writer and strategist. Her dedication to her craft and commitment to delivering high-quality work enables her to create compelling content that resonates with audiences.

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