The heterogeneous mixtures are those that present the naked eye in principle over a perfectly distinguishable component. It is said that they are composed of more than one material component or phase (solid, liquid or gaseous), which maintains or preserves all its properties regardless of the rest of the mixture.
These types of mixtures are very abundant here on Earth, where their elements are united by multiple natural processes or thanks to those invented by civilization. In fact, they can be observed in everyday life.
The way to know if a mixture is heterogeneous is by observing whether it has two or more material components or phases. Examples of homogeneous mixtures are a plate of rice with lentils, cereals with milk, coca cola with ice, a mixture of oil and water, orange juice with pulp, earth or sand. If you look closely, you can see that the earth and sand are made up of different components.
The material phases are the components of the heterogeneous mixture, which can be separated by applying different separation methods. These methods are generally physical, without the need to use chemical reagents, but especially mechanical work or heat.
Separation methods for heterogeneous mixtures include decantation , filtration, sieving, evaporation, dissolution, and magnetic separation.
There are heterogeneous mixtures that are homogeneous or uniform to the eye, causing confusion. However, when viewed under the microscope or at smaller scales, their distinguishable phases appear. These types of heterogeneous mixtures are known as colloids, although such a statement is often the subject of discussion.
Characteristics of heterogeneous mixtures
They are not uniform
The main characteristic of a heterogeneous mixture is its lack of uniformity, that is, that it looks the same or that its properties do not vary where it is looked at or analyzed. By having more than two distinguishable phases or components, according to the observation scale, uniformity is broken.
For example, the beach floor has sand particles, small stones, plant and animal material. Note that in this example, and in many others, the non-uniformity of the heterogeneous mixture is measured by the difference or contrast of their colors.
They have a predominant phase
Heterogeneous mixtures have a predominant phase, which is the one that is found in greater proportion than the others. This phase can be either solid, as in the case of sand grains, liquid or gaseous, and is commonly called the dispersing phase . Instead, the minority phase is called the dispersed phase .
They present more than one state of matter at the same time
Depending on the state of matter of the dispersing phase, as well as that of the dispersed phase, a group of heterogeneous mixtures is obtained whose characteristics are in complete agreement or not with the physical states of matter: solid, liquid or gaseous. For example, the beach soil is a solid smorgasbord. We will give other examples later.
Types of heterogeneous mixtures
Soil, fruit baskets, rice with lentils, and minerals from many colorful crystals are examples of solid heterogeneous mixtures. These are perhaps the simplest in terms of their method of separation, and they are also probably the most diverse.
Additional examples of solid heterogeneous mixtures will be discussed in the examples section.
The expression: ‘stars suspended in the sky’, helps to understand what suspensions are. This type of heterogeneous mixture consists of a predominant liquid phase, which houses or disperses small solid particles that can be appreciated with some effort.
For example, when water and sand are mixed and stirred in a glass, a suspension initially forms. However, as time passes, the same gravity ends up sedimenting the sand particles at the bottom of the glass, further demonstrating the irregular or non-uniform nature of the heterogeneous water-sand mixture.
What if, instead of sand, much smaller particles were dispersed that managed to remain stable for longer? We would then be facing a colloid, whose predominant or dispersing phase can be solid, liquid or gas.
The dispersed particles are so small that at first glance colloids fall into the classification of homogeneous mixtures due to their apparent uniformity. However, when analyzed under the microscope or at lower scales of observation, the colloid begins to show more than one phase or component.
The water-oil mixture is the classic example of a colloid called an emulsion, as it is composed of two immiscible liquids (which do not mutually dilute). Other colloids are blood, mayonnaise, and milk.
Note that these examples have in common that they appear homogeneous at first glance, and are not considered heterogeneous mixtures until they have been analyzed further.
Methods of separation of heterogeneous mixtures
There are many separation methods to obtain one by one the components of a heterogeneous mixture. Only the most important ones will be mentioned below.
Of all the methods, this is the simplest on a small scale. If we have a cupcake or cake with pieces of chocolate, these can be removed by the action of the same fingers or using tweezers. The same applies to rice with lentils, where the lentils would be patiently stirred with no other tools or instruments than our own hands.