Why does oil float above water?
This question identifies an observable fact that we witness often in our daily lives. We know that oil floats on water from our personal experience – you can see pools of oil on top of a puddle after a rainstorm or in the kitchen sink while washing dishes. Oil floats on water because of two factors: First, teaspoon for teaspoon oil weighs less than water. This makes oil buoyant in water, just like a cork or an air-filled rubber duckie stays on the water’s surface in a bathtub or bucket. Many, but not all, oils are less dense than water. You can demonstrate this by comparing the weight of a beaker of water with a beaker of oil. But that is not the end of the story, for example, most alcohols are also lighter than water, and they do not float. What is the difference? Oil molecules are hydrophobic (from the Greek meaning fear of water). Most familiar oils do not dissolve in water, instead the molecules cluster toward each other and then float up to the surface. If a large amount of oil is
