why do vegetable oil and water separate

What's happening? Oil and water are two liquids that are immiscible, meaning they will not mix together. Liquids tend to be immiscible when the force of attraction between the molecules of the same liquid is greater than the force of attraction between the two different liquids. Although this experiment uses the same volume of oil as water, the two liquids have different masses and therefore, different densities. Density is a measure of how much of a substance is contained in a specific volume of liquid. A liquid that is less dense than water will float on the water; a liquid that has a greater density will sink. To gain an understanding of density, think of two zippered plastic bags of the same size (same volume). Imagine that one bag contains 10 marbles and the other 20 marbles.


The bag containing 20 marbles is denser than the bag containing 10 marbles because it contains more material в even though it is the same material. This analogy describes the relative densities of different concentrations of the same substance. Also imagine that there is a third bag containing 10 very large marbles. The volume of the material is the same, the number of molecules (marbles) are the same but again, the bag of large marbles contains more material - it has a greater mass and so a greater density. This analogy represents the experiment above since two different materials are used. The objects added to the container will float at different levels according to their density. If the density of the object is similar to that of water, the object will float in the water.


If similar to the oil, the object will float in the oil. What does it matter? Getting oil and water to mix is at the very heart of cleaning dishes and clothes. A lot of agents that make dishes and clothes dirty are greasy or contain oil. Water alone is not attracted to these compounds. However, because a detergent has one end that is attracted to oil-like molecules, detergents tend to bind to dirt, grease and oil. The other half of the detergent binds to water molecules, allowing the soiling agent to be washed away. Investigate further! You can also try layering oil, water, pancake syrup and dish detergent in a narrow, cylindrical drinking glass or vase. Pour the liquids into the container slowly.


Let the container sit still for a few minute before observing. In what order do the liquids form layers in the container? What does this tell you about the density of each liquid?
What happens when Oil and Water mix? Have you tried to wash oily hands in just water and discovered that your hands stayed oily? Or think of crude oil that spills from a tanker in the ocean and floats on top of the water. There are two main reasons why donБt oil and water mix even if they are put in the same container. Both these reasons consider these two substances on a very small scale. Everything around us is made up of tiny particles known as molecules. The way in which two substances interact depends on the molecules that make up the substances.


The first reason that water and oil donБt mix is because their are packed differently. The molecules of water are packed very densely. (Would be good to show water molecules packed densely) In one glass of water, there are more molecules than the number of known stars in the universe! This means if we take equal parts of water and oil, there will be more molecules of water than oil. This also means that it will always sink underneath the oil. There is one more reason why they cannot mix with each other. Polarity. Polarity means a molecule is positively charged at one end and negatively charged at the other. Water is a polar molecule. Water molecules are made up of two hydrogen atoms and one atom each. Since only opposites attract, the water molecules stick to each other.


Polar molecules only dissolve in polar solvents. Similarly, non-polar molecules only dissolve in non- polar solvents. Oil is made up of non-polar molecules. It has a shell of negative charges, or electrons, surrounding the molecule. The oil molecules will ultimately stick to each other. Therefore, even if you stir a container with oil and water, they will eventually separate into two distinct layers. Detergents and soaps help us to remove oil and dirt from utensils and our bodies. Oily feathers and coats help animals who live in seas and rivers to stay warm, as the oil keeps the cold water away from their skin. THINGS TO DO Go to to watch a fun Density Test experiment and try to do it yourself.