Why do oil and water not mix?

Answer 1

Density is a red herring. If two liquids are miscible and have different densities they will mix together to form a solution with its own density. It is because of polarity.

Water molecules are dipolar, so they have one end that is partially positively charged (the hydrogens) and one end that is partially negatively charged (the oxygen). When you get a bunch of water molecules together they form a transient network of hydrogen-bonds, short-lived interactions between the oxygen of one water molecule and the hydrogen of a neighboring molecule. These hydrogen bonds explain water's unusually high boiling point, its decrease in density upon freezing, and its unusually high surface tension.

Oil is made of long hydrocarbons, which are nonpolar. Nonpolar molecules don't really have much incentive to stick to each other. They do experience very weak attractions called van der Waals forces when they are close to each other, but these are common to all molecules.

When you try to mix water and oil together the water "wants" to satisfy its hydrogen bonds. This is best done by sticking together with other water molecules. The hydrocarbons don't really "want" water there or not, but are happy to exclude water if it "wants" to go somewhere else. The result is a biphasic mixture. Oil ends up being the top layer because it is less dense than water, but there are also nonpolar liquids that are more dense than water, and in that case the aqueous phase would be the top layer. Sometimes the two densities are close enough that which one ends up being on the top is a matter of what else is dissolved in each solvent (seen sometimes in aqueous extractions with chloroform or dichloromethane--always check to make sure you've got the right phase before dumping the rest down the drain!)

Answer 2

ignore any body who recons its to do with density, they dont know there donkey from their elbow.

"oils" are long chain hydro-carbons (non-polar)
water is a small molecule H2O (Polar due to the large difference in electonegativity between hydrogen and oxygen) and polar and non polar molecules do not mix

sorry for the boring science lesson, basically oxygen is big compared to hydrogen thus pulls electrons towards itself making one side more -ve and one side more +ve.

In long chain hydro-carbons, the difference is cancelled out by the chain length, so the longer the chain, the more non-polar the molecule will be.

there are ways of making them mix

hope this helps

Answer 3

Water is polar, so will mix with other polar substances.
Oil is non-polar, and so will only mix with other non-polar substances.
Sugar is polar - you can dissolve sugar in water, but it won't dissolve in oil. There are other substances that water will not dissolve, but non-polar substances will, like nail-varnish etc.

Answer 4

Due to the volume oil being the greater oil always rises to the top...if both do become mixed it is then emulsified as when water mixes with car engine oil....then they take on the appearance of white sludge..

Answer 5

because water is more dense than oil therefore it lies beneath the oil and they do not mix

Answer 6

Because water can't penetrate oil because of oil's density.

Answer 7

coz of density..the oil is lighter than than water so they can't be mixed.

Answer 8

I believe because of density and polarity factore, sorry not much of a whiz in that area.

Answer 9

their different types of substance liquids
oil is thick and the molecules are hard to brake up making it hard to mix with the water

just like blood and food doesn't mix :)

Answer 10

number 1, it's because they have different densities..liquids with different densities don't mix :D
2nd, oil is non-polar while water is polar. only same polarities mix.. :D