Ethanol and water are miscible: they dissolve into each other completely and settle as ONE layer. A separating funnel only helps when a mixture forms two layers with a boundary you can split at. Here there is no boundary at all — so we need a method based on boiling points instead.
Simple distillation shines when the boiling points are enormously far apart — for example water (100 °C) and a dissolved solid like salt (well over 1000 °C). Ethanol (78 °C) and water (100 °C) are only 22 °C apart, so when the mixture boils, both liquids evaporate together. A simple still would hand you ethanol badly contaminated with water.
The fractionating column is a tall tube packed with glass beads, fitted between the flask and the condenser. The beads provide a huge, slightly cooler glass surface. Rising vapour has to fight its way past them, condensing and re-evaporating over and over — and every cycle leaves the vapour richer in the substance with the lower boiling point.
Turn the collar to close the air-hole first, then strike the sparkler over the top of the barrel. The gas lights with a yellow, wavy luminous flame — easy to see and safe, but cool and sooty. Opening the air-hole mixes air with the gas: the flame turns blue and roaring — the non-luminous flame, much hotter and clean, which is the one you heat with.
The bulb sits level with the side arm, so it measures the vapour that is about to leave. The reading holds steady at 78 °C while ethanol distils, rises when the ethanol is finished, then holds again at 100 °C while water distils. A flat reading tells you which liquid is coming over; a rising reading tells you the fraction has finished.
The moment the temperature climbs above 78 °C, whatever condenses next is no longer pure ethanol. If the first flask stays put, water drips in and contaminates the fraction you worked so hard to collect. Sliding an empty receiver in at the right moment keeps every fraction pure.
Every bead surface is one more condense-and-re-evaporate step. A longer column packs in more steps, so it can separate liquids whose boiling points are very close together.
| Simple | Fractional | |
|---|---|---|
| Mixture type | Solvent + dissolved solid (huge bp gap) | Miscible liquids with fairly close boiling points |
| Apparatus | Flask connected straight to a condenser | Bead-packed fractionating column between flask and condenser |
| Example | Pure water from salt water | Ethanol from an ethanol–water mixture; crude oil fractions |