Distillation: How We Separate Liquids by Boiling

Imagine you have a cup of salty seawater and you are very thirsty. You cannot drink it, because the salt would make you sicker. But there is a clever trick: if you boil the water, the water floats away as steam, and the salt stays behind. Catch that steam, cool it down, and it turns back into clean, drinkable water! That trick is called distillation, and chemical engineers use giant versions of it to make everything from clean water to the gasoline in cars.

In this lesson you will: - Learn what distillation does and why boiling point matters. - Follow the three steps: heat, evaporate, and condense. - See two real jobs distillation does in the world. - Build a safe model of the water cycle that works just like a distiller.

Every liquid turns into a gas at a certain temperature, called its boiling point. Water boils at 100 degrees C (212 degrees F). Salt does not boil until it is over 1,400 degrees C, which is far hotter. Because water boils SO much sooner than salt, we can heat the mixture just enough to boil off the water while the salt stays put. Distillation works whenever the things in a mixture have different boiling points.

1. HEAT: You warm the mixture until the liquid you want reaches its boiling point. 2. EVAPORATE: That liquid turns into a gas (vapor) and rises up, leaving the salt or dirt behind. 3. CONDENSE: The vapor touches something cool, loses its heat, and turns back into a pure liquid you can collect. Cooling a gas back into a liquid is called condensation.

Distillation does important jobs every day. On big ships and in dry countries, huge machines called desalination plants distill seawater into fresh water for people to drink. In an oil refinery, workers heat crude oil in a tall tower; because gasoline, diesel, and jet fuel all boil at different temperatures, they separate into different layers and can be collected one by one. One tower can separate crude oil into six or more useful fuels.