Wax does not dissolve in water. This inability to mix is a fundamental concept in chemistry, rooted in the contrasting molecular structures of the two substances. The physical separation seen when wax and water meet is a direct consequence of their different electrical properties, which dictates whether they can form a uniform solution.
The Chemistry of Wax
Waxes are classified as lipids, which are organic compounds that are hydrophobic, meaning they repel water. They are predominantly composed of long chains of hydrocarbons, molecules made almost entirely of carbon and hydrogen atoms. The structure of these long chains, such as those found in paraffin wax, is chemically non-polar.
A molecule is non-polar when electrons are shared almost equally between atoms, resulting in no significant separation of electrical charge. Without positive or negative ends, wax molecules rely on weak intermolecular attractions called London dispersion forces. These forces are not strong enough to interact with water, which is why wax is often used as a protective, water-repelling coating.
Understanding Water’s Polarity
In sharp contrast to wax, the water molecule (H2O) is highly polar. It consists of two hydrogen atoms bonded to one oxygen atom in a bent shape. The oxygen atom is significantly more electronegative than the hydrogen atoms.
This difference means the oxygen atom pulls the shared electrons closer to itself, giving it a partial negative charge, while the hydrogen atoms are left with a partial positive charge. This uneven distribution of charge creates a molecular dipole, giving the water molecule a positive end and a negative end. This polarity allows water molecules to form strong attractive forces with each other called hydrogen bonds.
The Rule of Like Dissolves Like
The question of whether two substances will mix is governed by the fundamental principle of solubility: “like dissolves like”. This rule means that a substance tends to dissolve best in a solvent that shares similar molecular properties and intermolecular forces. Polar solvents, like water, dissolve polar solutes because their strong charges align and attract. Non-polar solvents dissolve non-polar solutes because they interact using similar, weaker forces.
When non-polar wax encounters polar water, the two substances are chemically incompatible. The water molecules are much more attracted to each other through their strong hydrogen bonds than they are to the non-polar wax molecules. The water molecules effectively push the wax molecules aside, excluding them from the network of hydrogen bonds and causing the wax to remain separate and immiscible.
Solvents That Dissolve Wax
Because wax is a non-polar substance, it readily dissolves in other non-polar liquids. Non-polar solvents are effective because their molecules easily intermingle with the long hydrocarbon chains of the wax, overcoming the weak forces holding the wax together.
Practical examples of non-polar solvents that can dissolve wax include mineral spirits, turpentine, and various petroleum-derived hydrocarbons such as hexane and toluene. Even common cooking oil, a lipophilic substance, can act as a non-polar solvent to help remove wax.