Why Does Oil Float Above Water?

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    Floating Oil Water
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Discussion Overview

The discussion revolves around the question of why oil floats above water, exploring concepts of density, viscosity, and the behavior of different types of oil in various conditions. Participants examine the relationship between oil and water in the context of oil spills and the physical properties of liquids.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants assert that oil is less dense than water, which explains why it floats.
  • Others mention that viscosity may lead to confusion, as it is often mistakenly associated with density.
  • A participant suggests that a denser liquid could float atop a less dense one if surface tension is significant, but emphasizes that oil is less dense than water.
  • There is a discussion about how boiling water and removing dissolved oxygen might affect density, with some uncertainty about its impact on oil's behavior.
  • One participant explains that the molecular structure of oil (non-polar) and water (polar) contributes to their density differences.
  • Another participant notes that the density of crude oil can vary based on its source and conditions, leading to different behaviors in spills.
  • Some participants express confusion about the weight of equal volumes of oil and water, with clarifications about the meaning of density.
  • A question is raised about the behavior of vegetable oil over water, with anecdotal evidence provided about water sinking in practical scenarios.

Areas of Agreement / Disagreement

Participants generally agree that oil is less dense than water, but there are competing views regarding the implications of viscosity and specific conditions affecting density. The discussion remains unresolved on some points, particularly regarding the effects of dissolved gases and the behavior of different oils.

Contextual Notes

Some claims depend on specific conditions such as temperature and pressure, and the discussion includes references to various types of oil, which may have different densities. There is also mention of the complexity introduced by environmental factors in oil spills.

gunblaze
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Oil Floating above water...?

Someone, please first answer this qn...
Is oil denser than water?

If yes, pls proceed...

When an oil spill occurs at sea, why would the oil float above the water?
If oil is denser than water, wouldn't oil be sinking to the bottom of the sea?
Could anyone pls offer an explanation to this qn.Thx :rolleyes:
 
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Oil is less dense than water
 
oh...ok.Thx
 
Oil is usually more viscous (not dense) than water, perhaps this is the source of your confusion.
 
brewnog said:
Oil is usually more viscous (not dense) than water, perhaps this is the source of your confusion.

Humm.. viscousity has nothing to do with floating, density has everything to do with floating. Oil floats on water, therefore oil is less dense then water.
 
Integral said:
Humm.. viscousity has nothing to do with floating, density has everything to do with floating. Oil floats on water, therefore oil is less dense then water.
I think what Brewdog was referring to is the fact that the words "light" and "heavy" are often associated with the viscosity of oil. This could lead to confusion: http://www.lloydminsterheavyoil.com/whatislaunch.htm
What is Heavy Oil?

Heavy oil is a type of crude oil which is very viscous...
 
A denser liquid might float atop a less dense one if a sufficient surface tension developed at the interface layer (think of a needle made of metal floating atop water).
An oil, is however, less dense than water.
 
I heard if you boil water and let it cool down again, it removes a lot of oxygen in the water, thus making oil sink, instead of floating.

So maybe oil is denser than pure water, (H2O, nothing else) but not tap water?
 
  • #10
Gara said:
I heard if you boil water and let it cool down again, it removes a lot of oxygen in the water, thus making oil sink, instead of floating.

So maybe oil is denser than pure water, (H2O, nothing else) but not tap water?
I'm not sure to what extent your method would work but if you remove all of the dissolved air out of water it would make the water more dense so materials would have a higher tendency to float.

If you look at the chart that moonbear posted, every single item that's listed as an "oil" has a lower density than water.
 
  • #11


ummmm it has been 6 years later and i don't know if my response will mean anything to the people but i thought i would put it here anyway...part of your understanding lies in chemistry. Oil is composed of long chain hydrocarbon molecules so you would think it is more dense than water in that sense, but water is a polar molecule and will form hydrogen bonding with surrounding water molecules and hence, will be more closely packed giving a greater density since p=m/V. For oil on the other hand, it is a non-polar molecule and hence the only intermolecular forces holding the oil together are weak dispersion forces and hence the molecules of oil will want to be apart from each other as this is more 'energetically favourable', and hence oil is not packed tightly could be considered 'looser' and so appears less 'dense'.
Therefore the Force of gravity would act accordingly on the 'heavier' substance being water in this case, so oil is seen floating on top.
 
  • #12


Huh... never thought about it, but great explanations.
I must admit that I was under the impression that most liquids were heavier than water. Learn something new everyday!

Edit: perhaps it WOULD be correct to say that 1 fluid ounce of oil IS heavier than 1 fluid ounce of water.
But, the above post by shikobe explains how it can be different in a complex environment(polar/non-polar)
Hope I got that right.
 
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  • #13


pallidin said:
Edit: perhaps it WOULD be correct to say that 1 fluid ounce of oil IS heavier than 1 fluid ounce of water.
Um...no, that's exactly the issue that was being discussed!
 
  • #14


If you are talking about crude oil (the sort that you get in large spills), then the density and actual composition varies greatly, according to where it was extracted. I was listening to the radio, only today, aamof, and the Mexican Gulf spill has resulted in floating oil patches and large volumes of more dense oil sitting on the sea bed. The different fractions have clearly separated out. I wonder whether this was due to the action of bacteria - it couldn't have been the normal fractional distillation process as it never got hot enough.
 
  • #15


gunblaze said:
Someone, please first answer this qn...
Is oil denser than water?

What kind of oil? What temperature and pressure?

gunblaze said:
If yes, pls proceed...

When an oil spill occurs at sea, why would the oil float above the water?
If oil is denser than water, wouldn't oil be sinking to the bottom of the sea?
Could anyone pls offer an explanation to this qn.Thx :rolleyes:

At depth, crude oil can be denser than water- that is why the Deepwater Horizon spill was generally confined.to underwater plumes.
 
  • #16


Oh yes - I see that water has about double the modulus of oil(s) so, unless it is brought to the surface by stirring, oil will tend to stay at great depths.
 
  • #17


russ_watters said:
Um...no, that's exactly the issue that was being discussed!

OK, let me correct that.
I am under the assumption(perhaps incorrect) that a 16oz glass filled with oil is physically heavier than a 16oz glass filled with water.
What do you say?
 
  • #18


No! If it were, that would mean it was more dense. Oil is less dense than water. That's what "density" means!
 
  • #19


OK. Good enough for me. Thanks for clarifying.
 
  • #20
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  • #21


Can someone answer my question: if I have 10 ml of vegetable oil over 5 ml of water, will the oil still float over the water or will the order be reversed?
 
  • #22


cmendez79 said:
Can someone answer my question: if I have 10 ml of vegetable oil over 5 ml of water, will the oil still float over the water or will the order be reversed?

When I occasionally get water in the gas take of my lawn mower, the water sinks to the bottom. There would be a small layer of water underneath a large layer of oil.
 
  • #23


pallidin said:
After some research I found this:

1 gallon of water weighs approx. 8.35 pounds.
Source: http://wiki.answers.com/Q/How_much_does_one_gallon_of_water_weigh

1 gallon of oil weighs approx. 6-8 pounds depending on density.
Source: http://wiki.answers.com/Q/How_much_does_one_gallon_of_oil_weigh

You guys are right. Not sure how I felt that something "thicker" should weigh more.
Oh well, I learn something new each day.
Cheers!

The ultimate in 'thickness' would be 'solid? Manu solids are less dense than water and will float. 'Thickness' means viscosity usually - and is not 'density'.

Floating or sinking depends entirely on relative density.
 

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