Can polar and non-polar molecules ever mix?

Chemistry for non-majors

learning goals

  • Describe the solubility of non-polar compounds in water.

Does oil dissolve in water?

Deepwater Horizon Oil Spill, courtesy of NASA.

A major oil spill occurred in 2010 when an explosion on an oil rig in the Gulf of Mexico released millions of gallons of crude oil into the Gulf., Oil is primarily a mixture of hydrocarbons (organic compounds made up only of carbon and hydrogen atoms) . Due to its composition, oil does not dissolve in water. As a result, much of the Gulf of Mexico was contaminated, as was much of the coast in the affected area.

Liquid-liquid solutions

Non-polar compounds do not dissolve in water. The forces of attraction that act between the particles in a non-polar connection are weak dispersion forces. However, the non-polar molecules are more attracted to themselves than to the polar water molecules., When a non-polar liquid such as oil is mixed with water, two separate layers form because the liquids do not dissolve into one another (figure below). When another polar liquid like ethanol is mixed with water, they mix completely and dissolve into each other. Liquids that dissolve in each other in all proportions should be miscible. Liquids that do not dissolve in one another are said to be immiscible. The general rule for deciding whether one substance is able to dissolve another is “how does it dissolve”., “A non-polar solid such as iodine dissolves in non-polar lighter fluid, but does not dissolve in polar water.

Figure 1. Water and oil form separate layers when mixed because the non-polar oil does not dissolve in the liquid. The oil forms the top layer because it is less dense than the water. Flickr: Yortw.

For molecular compounds, the main factor that helps dissolve the material in water is the ability to form hydrogen bonds with the water solvent., Small compounds like methanol, ethanol, acetic acid, and acetone have polar groups that can interact with the polar H of water . However, as the non-polar part of the molecule becomes larger, the solubility with water drops. The non-polar part of the molecule increasingly repels water and eventually overwrites the interaction of the polar component with water.

Key takeaways

  • Non-polar molecules are usually insoluble in water.
  • A non-polarized molecule must be relatively polar in order to interact with water molecules.,

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Use the link below to answer the following question:

http://chemistry.about.com/od/factsstructures/ig/Chemical-Structures—E/Ethylene-Glycol.htm

  1. Explain why ethylene glycol dissolves in water.

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  1. What are the main forces acting between non-polar molecules?
  2. What part of a molecule is needed for this molecule to dissolve in water?
  3. List some organic molecules that dissolve well in water.

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  • immiscible: liquids that do not dissolve in each other.,
  • Miscible: Liquids that dissolve in all proportions.
  • polar: Molecule with partially negative and positive charges