Mixing oil with vinegar produces a short-term blend.
You prepare a salad and get ready to pour on oil and vinegar, but you notice that the oil and vinegar form two layers in the container -- making it necessary to shake the container to remix the liquids. Next time you use the oil and vinegar, you see the same separation. Although both oil and vinegar are liquids, not all liquids mix to form a solution. A few factors contribute to why they separate.
Vinegar
Water and acetic acid combine in a solution to make vinegar, according to Elmhurst College. Water contains hydrogen and oxygen atoms, and acetic acid contains carbon, hydrogen and oxygen atoms. The hydrogen connects to the other atoms in strong bonds. Hydrogen bonds help explains how things float on water or why water drops form. Vinegar typically contains less than 10 percent acetic acid and a small amount of minerals and other particles.
Oil
Oil molecules bonds, though not as strong as the water molecule bonds, stick to other oil molecules with greater attraction than for water molecules. Oil molecules have a weak attraction to water -- but not strong enough to break the water molecules. Shaking or stirring vinegar and oil makes the liquids mix temporarily; however, the molecular attraction of the water-to-water and oil-to-oil soon results in the liquids separating.
Density
In the container, the oil and vinegar separate from each other in the same pattern each time, with the oil on the top and the vinegar on the bottom. The oil ends up on top regardless of the amount of each liquid because the higher density or heaviness of the vinegar causes it to sink to the bottom. The same thing occurs with oil spills that float on the water.
Chemistry
Sometimes someone comments that two people have no chemistry -- implying that the persons involved lack a strong attraction to each other. Oil and vinegar lack a strong attraction. In chemistry, emulsion occurs when items do not mix. If you add an emulsifying agent to the oil and vinegar, then it makes it possible for them to form a stabilized mix or emulsion. Mayonnaise contains oil and vinegar and egg yolks that act as the emulsifying agent. Other emulsifying agents for mixing oil and vinegar include starches and powders that form bonds with both the oil and vinegar to keep them mixed.
Tags: acetic acid, both vinegar, each other, emulsifying agent, float water
