TECHNIQUES FOR SEPARATING MIXTURES

4.1 For heterogeneous mixtures

There are a variety of techniques that allow separating the components of a heterogeneous mixture. They are all physical methods based on the different value of a property of the components of the mixture, such as whether they are in the same or a different state of aggregation, their density, or their size. Some of them are shown in the box below, although there are many others that you will learn about later.

Techniques for separating heterogeneous mixtures

This consists in the separation of the components of a heterogeneous mixture if they have different densities. It may be a mixture of immiscible liquids (which do not dissolve, such as water in oil), or of a solid suspended in a liquid or gas.

For two immiscible liquids, pour the mixture into the separating funnel, as in the figure. After a certain time, the less dense liquid floats. Then, open the tap to separate the denser liquid, which can be collected in a beaker.

If we have a mixture of a solid and a liquid, it will be possible to separate the larger particles of the solid using a filter, or a filter medium.

The filter paper in the image retains the solid particles, while the water passes through it.

The separation is obtained because the components of the mixture have different densities.

In this case, the mixture goes through the action of a centripetal force, caused by a high-speed rotary motion.

This technique is used to separate heterogeneous mixtures for which decanting or filtration is not sufficient, e.g., to separate plasma from blood.

4.2 For homogeneous mixtures

Separation techniques for homogeneous mixtures allow the solvent to be separated from the solute or solutes. The two most commonly used ones are described below.

This technique is indicated when we have a solid solute, such as a salt, dissolved in water.

It consists of evaporating the solvent to obtain a saturated solution, in which the solid will begin to precipitate. To do this, pour the solution into a crystalliser. Once the solvent has evaporated, we will have salt crystals.

Distillation

Distillation allows separating a solution consisting of two liquids with different boiling temperatures.

Place the solution in a round-bottomed flask and heat it. When the boiling temperature of the most volatile substance is reached, it changes to a gaseous state. The vapours generated pass into the inner tube of the coolant, where they condense and are collected in the collector. Cooling water flows through the outer coolant tube, which cools the vapours without coming into direct contact with them.

Review the presentation on anayaeducacion. es again to remind yourself how to use the lab equipment.

Understand, think, investigate

17 Make a hierarchical diagram with the classification of mixtures and the separation techniques that can be used in each case according to the state of aggregation of the substances that form the mixture and the property on which each separation technique is based. Use the diagram on the right.

18

Thinking heads. You have a sample of a residue consisting mainly of sand and water. You also observe a viscous liquid in this mixture that appears to be oil. You are asked to determine whether there are also dissolved salts. How would you go about separating the components of this mixture?

Types