Written by: on April 21, 2020 @ 6:00 am

If you’ve ever seen oil and water interact, you know some things simply don’t mix! Like cats and dogs, oil and water refuse to get along and work together! Oil and water didn’t get into a fight, but instead they have differences at the very smallest unit… molecules!

All things are composed of matter, from your body to your chair. Chemistry, the study of matter, works to understand how all matter works and interacts. All matter is composed of molecules, the tiniest particle that matter is composed of. To understand how matter will behave, chemists must understand how these molecules work. Atoms are the basic unit of an element, such as oxygen or aluminum, and these atoms form together to create larger molecules.

Let’s take a look at the molecules of oxygen and oil to understand why they do not mix! Water molecules are polar, meaning one side of the molecule has a positive charge while the opposite side has a negative charge. Water’s polar charge helps the molecules to bond together; other substances with polar molecules such as sugar, salt and ammonia will easily bond with water! Unlike water and some of water’s closest friends, oil is non-polar, meaning that the molecule has a uniform charge.

Due to opposing polarity of water and oil, the molecules can’t bond together! Water molecules will attract other water molecules while oil molecules attract other oil molecules. As these two substances stick together, they form a visual rivalry and separate themselves. Oil will float to the top of water; this is because water is denser than oil. Density means there are more molecules of a substance within a given volume, making one substance heavier than another.

If you take a bottle of oil and water and shake it, you can get the two to mix temporarily before they separate back into themselves. This is called emulsion, or the mixing of two liquids. To get water and oil to mix for a longer period of time, you can use an emulsifier. An emulsifier is a substance that has a molecule with one polar end and one non-polar end, and it is able to attract both water (polar) and oil (non-polar). Soap is an excellent example of an emulsifier and can be used to break down oil into water!

See water and oil molecules in action! Witness their molecular battle by building your very own density tube today!

https://sciencemadefun.net/downloads/bottle2.pdf

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