Polarity & Solubility
- Small polar molecules (like Ethanol) are water soluble.
- Long hydrocarbon chains (like Hexane) are non-polar and insoluble in water.
- More -OH groups generally mean higher solubility in water.
Key Concepts
Electronegativity
The measure of an atom's ability to attract shared electrons. Differences in electronegativity create polar bonds.
"Like Dissolves Like"
Polar solvents (like water) dissolve polar solutes. Non-polar solvents (like hexane) dissolve non-polar solutes.
Hydrogen Bonding
A strong type of dipole-dipole attraction that significantly increases boiling points and solubility in water (e.g., Alcohols).
Structure Reasoning
Why is Ethanol soluble but Hexanol less so?
Both have an -OH group (polar part). However, Hexanol has a long 6-carbon chain (non-polar part) that "overpowers" the polar group, making it much less soluble in water than Ethanol (2 carbons).
🧬 Biological Relevance
Solubility affects how drugs are absorbed in the body. Cell membranes are largely non-polar (lipid bilayer), so non-polar drugs can pass through them more easily than polar ones.
Example: Water vs Oil
Water is highly polar due to its O-H bonds. Oil consists of long non-polar hydrocarbon chains. Because there is no attraction between the polar water molecules and non-polar oil molecules, they do not mix.