Solutions Intermolecular Forces Compounds  Elmhurst College
Review of Solutions: Solubility of Polar Solutes Temperature & Pressure  Chemistry Department
Solubility of Salts Non-polar Solutes    Virtual ChemBook

Solubility of Non-Polar Solutes

NON-POLAR SOLUTE - NON-POLAR SOLVENT:

In all types of non-polar compounds, about the only intermolecular attractions are the very weak induced dipole forces. The weak attractive forces formed by the solute-solvent molecules compensate for breaking those weak bonds in the two pure non-polar substances. An example is solid iodine (I2) dissolved in liquid bromine (Br2). Shown on the left.

In addition to diatomic molecules with identical atoms, the most common type of non-polar compounds are the hydrocarbons. Many C-C and C-H non-polar bonds are present. Hydrocarbons are present in oils, grease, fats, dry cleaning solvents, turpentine, and gasoline.

Demonstrations with Solubility:
Disappearing Cup
Packing Peanut Race
Revealing Fingerprints
Deep Purple Magic

NON-POLAR SOLUTE - POLAR SOLVENT:

Non-polar Iodine is not very soluble in water. An intermolecular bond between an induced dipole (I2) and a polar bond in water is not very strong compared to the hydrogen bonds in water. The water molecules would rather remain hydrogen bonded to each other, then to allow an iodine molecule come between them. The water molecules effectively "squeeze" out the non-polar iodine. The intermolecular forces are not roughly equal, therefore, the "unlike" substances are not soluble in each other.

Various gases such as O2, N2, H2, CO2 are not very soluble because the gases are essentially non-polar. Of course you may say that oxygen must be dissolved in water to sustain fish life -- true, but the solubility is very low. Carbon dioxide is soluble in water such as carbonated beverages -- again this is true but why does it fizz when opened or lose the bubbles on standing? Carbon dioxide is not very soluble in water.

Demonstrations with Solubility:
Flaming Wood Splint
Deep Purple Magic
Lava Lamp
Dancing Raisins

Micelles and Detergents have many application of the solubility of polar and non-polar substances.

Polar - Non-Polar Properties of Proteins and Enzymes:

Many large molecules both inside and outside of the cells, must literally navigate through a watery-aqueous environment. These are molecules of lipids and proteins may be largely non-polar. In order for these molecules to be soluble in water they must have some polar groups exposed to the water.

In the graphic on the left the protein insulin is shown in two views. The interior of the protein shown in gray is non-polar - so these clump together "likes dissolve likes".

On the outside of the protein are largely polar groups shown in red which are able to interact with the polar water molecules - thus the entire protein is soluble.