What is Separating Mixtures?

Many of the substances we use every day were once part of the mix. Someone somewhere ripped these out of the mix so we could use it. It turns out that many compounds and elements are not found in nature in pure form but are found as part of mixtures. The separation of substances from mixtures is an important part of modern chemistry and industry.

Several important chemical terms are used in this section, including mixtures, suspensions, and solutions. You can click on the link to learn more about each of them.

Why do we want to separate Mixtures?

Since ancient times, diligent people have been separating mixtures to obtain the specific substances they need. An example is mining metal from ore to make tools and weapons. We will discuss other examples of separation below.

Separation Processes

The way in which different substances in a mixture are separated is called a process. There are several different processes used for separation. Many of them are very complex and involve dangerous chemicals or high temperatures. Today, many important industries in the world are based on separation processes.

Filtration

A common separation method is filtering. Filters are used everywhere. We use them in our homes to filter dust and dust mites from the air we breathe. We use them to filter impurities from our water. We even have filters in our bodies, such as the kidneys, that act as filters to remove bad things from the blood.

Filtration is commonly used to separate suspended mixtures in which small solid particles are suspended in a liquid or in the air. In the case of water filtration, water is forced through a sheet of paper made up of a very fine mesh of fibers. The water that has passed through the filter is called the filtrate. The particles that are removed from the water by a filter are called sediments.

Distillation

Another common separation process is called distillation. Distillation uses boiling to separate a mixture of liquid solutions. It should be noted that different substances in a mixture will have different boiling points.

For example, if you heat brine, the water in the solution will boil before the salt. Then the water will evaporate leaving the salt. If steam is collected, it will return to liquid form on cooling. This cooled water will be pure water with no salt at all.

Centrifuge

In some cases, there are suspended mixtures in which the solid particles are too fine to be separated by a filter. In these cases, a centrifuge is sometimes used. Centrifuge is a mechanical device that rotates at a very high speed. These high velocities allow the solid particles in the suspension to settle very quickly. For example, instead of waiting for sand to slowly settle to the bottom of the water, a centrifuge can cause the sand to settle in seconds.

Some examples of centrifuge uses include separating blood into plasma and red blood cells, separating cream from milk, and separating uranium isotopes for nuclear power plants.

Other Processes

There are many other separation processes such as sublimation, adsorption, crystallization and chromatography. Sometimes it takes several process steps to get to the final result. An example is crude oil processing. Crude oil uses multiple levels of fractional distillation to produce a number of different products, including gasoline, jet fuel, propane, and fuel oil.

Interesting Facts about Separating Mixtures

To separate liquid solutions in which the substances have similar boiling points, a more complex version of distillation is used, known as fractional distillation.

The picture uses evaporation separation. Wet paint is a mixture of pigments and solvents. When the solvent dries and evaporates, only the pigment remains.

The wheat separation process was used in ancient cultures to separate the wheat from the husk. They toss the mixture into the air and the wind blows the lighter ball away, leaving the heavier one behind.

The high-speed centrifuge can rotate up to 30,000 times per minute.

Many cleavage processes occur continuously in nature.