There are many substances that exist in our world, made up of multiple molecules that join together in various ways to generate complex compounds and structures.

Some substances are configured by the same type of element or substance, such as gold or silver, but many others are compounds formed by multiple types of substances, generating different types of mixtures with different properties.

Although they could be classified in multiple ways, as a rule we can find homogeneous mixtures or heterogeneous mixtures, being about the latter the ones we are going to talk about throughout this article.

What is a heterogeneous mix?

Heterogeneous mixture is understood to be any substance or material formed by the union of two more substances, which are combined but not joined together in a non-uniform way. In this type of mixture, therefore, the components are unevenly distributed: if we take two fragments or parts of it, it is likely that we will not observe the same proportions in the compound and even the same components.

In contrast to homogeneous mixtures, all components of homogeneous mixtures retain their individual properties and are separable and even directly visible, usually even to the naked eye (although microscopes are required for some subtypes of mixtures). The substances forming part of the heterogeneous mixture can be in any state of matter, whether solid, liquid or gaseous .

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Most heterogeneous mixtures are suspensions, which usually tend to be mixtures of one or more liquids and a liquid and a solid. Formed by a dispersed phase or non-soluble particles and a dispersant, it is a type of mixture in which one of the components remains suspended in another. As a rule, this type of mixture is not stable, and its components tend to separate, forming sediments unless other components are added to help stabilise them.

We can find multiple examples of heterogeneous mixtures in nature or among the products we use in our daily lives: smoke or air pollution, the air itself, sand from the beach, granite, ice cream, Roquefort cheese, blood, most drugs or mixtures such as water and oil, caesar sauce or salads.

How can its components be separated?

As we have mentioned, one of the properties of heterogeneous mixtures lies in the fact that it is possible to identify and even separate their components. Although in some cases these mixtures separate themselves by means of sedimentation (think for example of a mixture of water and oil), in some cases it may be necessary to use some kind of procedure to separate their components.

In this sense, we can achieve this separation by simple filtration , especially when we are dealing with a heterogeneous mixture in which there is a solid and a liquid component. Other methods can be magnetisation (with which we would manage to separate the non-soluble metal components from a liquid) or centrifugation (taking advantage of the centrifugal force, the separation of the components with a different weight is forced.

Colloidal dispersions or mixtures: a subtype of heterogeneous mixture

Another type of mixture that is technically a heterogeneous mixture despite the fact that it has characteristics that also bring it closer to the homogeneous ones, and that in fact are sometimes classified separately as an intermediate point between a homogeneous and a heterogeneous mixture, are colloids or colloidal dispersions.

The colloids are mixtures of homogeneous appearance composed by two or more elements in which one or more of them remain in permanent suspension in the other , being the first one the colloid particle (also called dispersed phase) and the second one a fluid (or dispersing phase). In other words, these are mixtures in which one or more of the components remain in the form of microscopic specks or drops that remain stable and do not separate.

However, its composition is not the same over its entire surface, so at a microscopic level its components could be distinguished. Within this type of mixture we can find different subtypes.

1. Emulsions

Emulsions are mixtures in which a liquid is dispersed in a solid or other liquid, something present in products such as milk, mayonnaise or gum .

2. Foams

Foams, such as the one visible in beer or shaving foam, are heterogeneous colloidal mixtures in which a gas is dispersed on a liquid .

3. Aerosols

In aerosols the dispersed phase can be either a liquid or a solid, while the dispersing phase is gaseous. Among this type of mixture we can find elements as common as smoke, fog or clouds,

4. Solid suns

These are colloidal mixtures in which both colloidal particles and fluid are solid elements. This is the case of alloys such as steel .

5. Gels and suns

Gels and suns are also a colloidal mixture, made up of a solid that is dispersed in a liquid (gels are semi-rigid solids). Custard or sludge are typical examples.

Bibliographic references:

  • Chamizo J. A. (2006). Models of Chemistry, Chemical Education, 17, 476 – 482.