Chapter 23
Section 2
Dissolving without Water
When Water Won’t Work
Water often is referred to as the universal solvent because it can dissolve so many things. However, there are some things it can’t do.
It can’t dissolve lipstick stain,
It can’t clean an oil-soaked bird.
Water can’t dissolve some solutes because of its polarity.
Non-polar materials have no separated positive and negative areas.
Because of this they do not attract a polar material, which means they do not attract water molecules. Nonpolar materials do not dissolve in water except to a small extent, if at all.
Example: Italian dressing. Oil and vinegar do not form a solution. You must shake it up first.
Most salad oils contain large molecules made of carbon and hydrogen atoms, which are called hydrocarbons. They share their electrons evenly. This equal distribution of electrons means that the molecule has no separate positive and negative areas. Because it has no charge separation, the nonpolar oil molecule is not attracted to the polar water molecules in the vinegar solution. That is why you shake it up.
Versatile Alcohol
Ethanol – is a substance that forms solutions with polar as well as nonpolar solutes because their molecules have a polar en a nonpolar end.
Uses of Nonpolar Molecules
Mineral oil – used as a solvent to remove candle wax from glass or metal. Can also be used to remove bubble gum from some surfaces .
Oil based paints – contain pigments that are dissolved in oils. Painters use turpentine to dissolve nonpolar paint.
Gasoline
Dry Cleaners – use nonpolar solvents when removing oily stains. The word Dryrefers to the fact that no water is used in the process.
Toxicity
Nonpolar solvents are flammable. They are also toxic. (This means it will kill you!!!)
It is important that you have good ventilation when exposing some of these materials.
How Soap Works
The oils on human skin and hair keep them form dying out, and the oils can also attract and hold dirt. (This is how you get zits.)
The oily dirt is a nonpolar mixture, so washing with water alone won’t clean the dirt.
Soaps are salts of fatty acids. When soap is made, the hydrogen atom of the acid group is removed, leaving a negative charge behind, and a positive ion of sodium or potassium is attached.
Thus, soap has an ionic end that will dissolve in water and a long hydrocarbon portion that will dissolve in oily dirt.
Polarity and Vitamins
The B vitamins and vitamin C are polar compounds. They dissolve readily in the water present in cells throughout your body.