Separation Techniques

Separation techniques

Filtration, evaporation, distillation, flotation, decanting, and sieving.

Why separation?

It's often important to separate mixtures to protect the health of people and the environment.

For example, the combustion engines in cars and buses are designed to separate out tiny carbon particles. This prevents them from polluting the atmosphere. A similar separation system is built into gas masks to protect workers in dangerous environments.

Physical properties

Pure substances have unique physical properties, such as density, state of matter, melting point, boiling point and solubility. Scientists need to understand these physical properties to distinguish one pure substance from another.

Techniques used to separate mixtures rely on differences in the physical properties of the components. In this lesson, we'll look at a few of the most important separation techniques.

Filtration can be used to separate insoluble solids from a liquid. It uses a filter. The holes in a filter are usually too small to see, but solid pieces get trapped whereas the liquid and anything soluble pass through.

Example: When a mixture of sand and water is poured through filter paper in a funnel, the sand particles remain as a solid residue in the filter paper, while the water is collected in the beaker below as a liquid filtrate. 

If the water has salt dissolved in it, the salt passes through the filter paper into the filtrate.

Filtration separates on the basis of differences in particle size and solubility.

Filtration

Multiple Choice

Identify which of the following can be separated by filtration.

• Two liquids

• Two solids

• A solid and a liquid

• A gas and a liquid

Evaporation is a method that recovers solid substances dissolved in a liquid. It recovers the solute from the solution by evaporating away the solvent, but not the solute.

Example: Salt can be collected from a salt water mixture by evaporation. The liquid water evaporates to leave the salt behind, since water has a much lower boiling point than salt.

Evaporation separates on the basis of differences in boiling point.

Evaporation

Simple distillation is an extension of evaporation. It's used to recover a pure liquid substance from a solution. The solution is heated to evaporate the solvent. But unlike simple evaporation this solvent, which is now in gaseous form (a vapour) is collected. It is cooled to condense it back into liquid in a separate container.

Example: A mixture of salt and water is heated to just over 100°C in a special distillation flask. 100°C is over the boiling point of water so the water turns into vapour. 100°C is well below the boiling point of salt, so it stays in the flask. The water vapour passes into a cooling tube which condenses it back into liquid water so it can be collected as distillate. The salt has been left behind.

Simple distillation separates on the basis of differences in boiling point.

Distillation

Multiple Choice

What is the main idea for distillation?

• Evaporation the substances

• Boiling points of substances

• How heavy each substance is

• How the substances move

Flotation can be used to recover a solid or a liquid from another liquid depending on which components sink or float.

Example: If sawdust and sand are stirred into water, the sawdust floats and the sand sinks, because the sawdust is less dense than the water and the sand is more dense than the water.

Another example of this is if oil and water are stirred together. The oil will float on top of the water as it is less dense than the water.

Flotation separates on the basis of differences in density. A less dense component will float to the top of a liquid where it can be skimmed or poured off and a more dense component will sink to the bottom.

Flotation

Multiple Choice

Select the physical property that flotation relies on.

• Density

• Particle size

• Solubility

• Boiling point

Decanting is the process of carefully pouring off the top layer of liquid from a mixture to separate it from the sediment or precipitate settled at the bottom. This technique is often used when the solid particles settle out of the mixture under gravity.

Decanting

Sieving is a method of separating particles based on their size. A sieve, typically a mesh or screen with uniform holes, is used to separate particles of different sizes. The smaller particles pass through the sieve, while the larger particles are retained.​

Sieving

These separation techniques are essential tools in various industries and scientific fields, allowing for the efficient separation and purification of substances for further processing or analysis.
Each technique offers unique advantages and is selected based on factors such as the properties of the substances being separated, the desired purity of the products, and the specific requirements of the application.

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Let's check your understanding from this lesson.

Quiz time