SCSP

Refining petroleum is a good example of separating a mixture into its components.

The most familiar product from a refinery is the gasoline that goes into your car.  However, this is just one small fraction of the products that come out of a petroleum refinery.

The  starting product is crude oil. This is usually drilled out of the ground or from under the sea at various places (Middle East, North Sea, South America, Southern US, Western US, Alaska etc). This raw product then is piped or shipped to an oil refinery.

The purpose of a refinery is to "fractionate" the crude oil into more useful parts. The crude oil can be considered a mixture of several different compounds. The crude oil is sent to a distillation tower where it is heated up. When heated, some of the oil will vaporize and rise up the tower. Because different parts of the oil boil at different temperatures – in general the "lighter" components boil at a lower temperature and the "heavier" components boil at a higher temperature – the lighter components in the vapor will keep rising when heavier components will start to condense.  So the components are separated bottom to top, heavy to light.  This allows the refinery to collect the different "fractions" of the crude.

Useful Products
The very top fraction from the distillation column is the light gases – such as ethane (C₂H₆) and propane (C₃H₈), which is used in some gas burners.

Gasoline is also a light fraction (though not as light as the light gases) – it usually consists of compounds containing 5-10 carbon atoms per molecule.

Kerosene (like the kerosene oil needed for lamps) is slightly heavier than gasoline.

The fuel that diesel trucks use is heavier than that used by cars. The diesel truck engine and the car engine are different and require different types of fuel.

The heavier fractions from the distillation column are not as useful. The heaviest part (which often does not boil) can be made into asphalt, which is used to surface roads. However, most of the heavy fraction can be sent to the rest of the refinery to be broken down and remade (through cracking and reforming) into the more useful lighter fractions.

Application to the Mixtures and Solutions Unit - If you heated a mixture of water (boiling point - 100° C or 212° F), ethanol (boiling point - 78° C or 172° F) and diatomaceous earth, the ethanol would start to boil first because of its lower boiling point. This would represent the light fraction. As the boiling continued, the vapor (a mixture of ethanol and water) would become progressively enriched in water, representing the middle fractions. What would not boil off would be the diatomaceous earth, which would be analogous to the really heavy fractions that make asphalt.