This is because oil is less dense than water and therefore it floats to the surface.

Water molecules cling strongly to one another by forming these bonds from one molecule to another. Surfactants such as dish soap break up water’s surface tension. As a result, objects floating in water will sink or change shape as the surface tension changes.

Vinegar is about 95-98 percent water and 5-2 percent acetic acid. Olive oil is made of lipids, long chain hydrocarbons. When you mix the two the oil wants to float on the vinegar, but for a short period of time the surface tension of the two liquids holds them apart. The oil floats on the vinegar.

Gravity separation is the most widely used method for oil emulsion separation. The elements in the well stream such as oil and water have different gravities. The density differences allow water to separate by gravity. With enough time in a non-turbulent state, the differing specific gravities will naturally separate.

Two immiscible liquids, oil and water, can be separated by using Separating Funnel. The mixture of oil and water forms two separate layers because they are completely insoluble in each other. Oil forms the upper layer while water forms lower.

However, it takes time for the oil to separate. Depending on the difference in density between oil and water, the temperature, the size of the oil droplets in the mixture and the type of oil, the separation may take from minutes to days. This is the situation with pure water and pure oil.

Distillation Methods The first uses a high-boiling-point water-immiscible liquid such as a mineral oil. The sample is suspended in this oil and heated to a temperature high enough to allow the water to be vaporized. The two liquids separate, and the water layer is measured.