Those tiny dots on the outer surface of an orange peel are oil glands. Squeeze the peel and they burst, releasing a natural oil called d-limonene — the chemical that gives citrus its sharp, fresh smell.

Here is the key idea: limonene and water don't mix — but limonene and rubber do. This comes down to a rule that explains a huge amount of chemistry: like dissolves like. Water is 'polar' — its molecules have a slightly positive end and a slightly negative end, like a tiny magnet. Oil is 'non-polar' — no charge at either end. Polar things are attracted to other polar things. Non-polar things are attracted to non-polar things. Opposites do not attract here — they ignore each other.

Latex — the rubber in a balloon — is also non-polar. Think of it as a stretchy fishing net made of molecular chains, woven tightly together and pulled taut by the air pressure inside. When limonene touches latex, it's like two things that speak the same language finally meeting — the limonene molecules slip into the gaps between the rubber chains, loosening them the way water soaks into a rope and softens every fibre. The network weakens. The air pressure hasn't changed — it's been pushing outward the whole time. When the weakened spot can no longer hold, it gives way.

Important for the classroom: nothing new was created here. The limonene is still limonene; the rubber is still rubber — just loosened and spread apart. This is a physical change, not a chemical reaction. Many popular science videos get this wrong and call it a chemical reaction — it isn't. A chemical reaction makes something new. Dissolving just moves things around. Ice melting, sugar dissolving, rubber softening — all physical changes.

D-limonene is also the active ingredient in many citrus-based cleaning products — it removes grease from engines and hands by the same like-dissolves-like principle.

See [Dino Snot Slime] for how a polymer network is built from scratch — and [The Sweet Lab] for another physical change that looks chemical but isn't.