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Q & A: Oil affecting evaporation of water

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Q:
Does oil effect the evaporation of water?
- Ray (age 10)
St Teresa of Avila, NY
A:
Sure!

Oil evaporates very slowly. Oil doesn't mix with water, and most oils are less dense than water. So oil floats on top of water, and usually makes a very thin layer, covering all the water you have, or else it spreads out until the oil layer is just one or two molecules thick and you run out of oil.

When the oil is covering the water, it prevents water molecules from evaporating, just like putting a lid on a jar.

Tom

(republished on 07/24/06)

Follow-Up #1: oil evaporation

Q:
does oil evapoate
- teddy archer (age 13)
A:
Sure, but many oils evaporate very slowly at ordinary temperatures.

mike W,

Lee H


(published on 03/03/07)

Follow-Up #2: oil and water evaporation

Q:
Does the thickness of the layer of vegetable oil on top of water affect the evaporation rate of the water and does it vary with the thickness of the oil?
- William (age 12)
KS
A:
Yes, the thicker the oil layer the slower the water diffusion through it to the surface, so the slower the evaporation. The type of oil will also matter, because the solubility of water in different oils is different, so different concentrations of water will be moving through different types of oil. Also, the diffusion rate will be different in different oils, and 'thicker' ones (more viscous) will tend to have slower water diffusion. However, I suspect that the water solubility will vary more between different oils than will the water diffusion rate.

Mike W.

(published on 12/02/07)

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