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What are heterogeneous mixtures?

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.

This type of mixture is very abundant here on Earth, where its elements are united through 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.

They are not uniform

Beach sand is a smorgasbord

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

Microscopic representation of a heterogeneous mixture. The gray points would be stones, the white smaller stones or vegetable or animal particles, and the bottom the sand particles.

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 completely consistent or not with the physical states of matter: solid, liquid or gaseous. For example, beach soil is a solid smorgasbord. We will give other examples later.

Types of heterogeneous mixtures

Solid

Soil, fruit baskets, rice with lentils, and minerals in many colorful crystals are examples of solid heterogeneous mixtures. These are perhaps the simplest in terms of their method of separation, and they are probably the most diverse as well.

Suspensions

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.

Colloids

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 gaseous.

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 observation scales, 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.

Oil pouring over glass of water

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 for separating 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.

Handbook

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.

Decantation

It consists of separating a liquid from a solid by the simple action of pouring, without the need for a filter or sieve. Settling could be used to separate the water from the settled sand at the bottom of a glass or container.

Filtration

It consists of separating a solid from the liquid through the use of a filter, which retains the solid particles while allowing the liquid to pass through. This method could be applied to the freshly prepared sand-water suspension, without having to wait for the sand to settle. Leakage is extremely recurrent or frequent in laboratory work.

Sieving

Similar to filtration, we have sieving, which is used to separate the components of a solid heterogeneous mixture according to the difference in size of their grains. This method would be used for example to separate the sand from some more robust or large stones.

Evaporation

Evaporation is usually reserved to separate the components of homogeneous mixtures, such as solutions. However, it can also be applied to break the apparent uniformity of certain colloids. Through heat, the lower- boiling liquid will evaporate first, leaving the other components behind.

Low pressure evaporation can be used to separate the fat and protein from the water that makes up the milk. This is one of the most essential steps in obtaining powdered milk.

Dissolution

The dissolution separation method is reserved mainly for solid heterogeneous mixtures, especially those of the mineralogical type. Impurities, visible on the surface, are removed by bathing the mixture in water or dilute hydrochloric acid, so that it becomes uniform.

Magnetic separation

Similar to the previous case, the magnetic separation is applied mainly for solid mixtures, where at least one of the components must respond to the attraction of the magnetic field of a magnet. Iron particles represent the classic example of a component that can be separated by this method.

Examples of heterogeneous mixtures

Cupcake or cake

Chocolate chip muffins are an example of a smorgasbord

The cupcake or cake itself, including all the ingredients that formed it during its preparation, becomes a material phase recognizable at first glance. Meanwhile, the chocolate drops, jutting on the surface, represent another solid material phase.

Jupiter crust

Planet Jupiter . Source: Judy Schmidt (https://www.flickr.com/photos/geckzilla/44790657805)

The gaseous crust of the planet Jupiter has more than one distinguishable phase, and even contains a huge reddish spot. This non-uniformity, along with its uneven appearance, is typical of a smorgasbord on massive scales. The deeper you go in the direction of the core of Jupiter, the more heterogeneous the picture becomes.

Mixed salad

Salad dishes stand out for their striking heterogeneity

Moving on to the culinary industry, the mixed salad is an excellent example of an everyday smorgasbord. Note that its components can be separated by manual method. Like salad, canapes or any other appetizer is classified as a smorgasbord.

Parterres (garden with plants and flowers)

In the flowerbeds you can see more than one conglomerate of flowers

Flowerbeds are another example of heterogeneous mixtures, in which flowers are its components. Again, the more flowers there are, and the more different their colors, the more heterogeneous the flowerbed will look. This case is similar to that of the snack or any cluster of sweets.

Ham bread

Slice of ham bread. Source: Veronidae via Wikipedia.

The ham bread, a typical gastronomic element in the December festivities in Venezuela, is another good example of a heterogeneous mix due to its raisins, ham, bacon and olives.

Soda

Carbonated drinks are considered heterogeneous mixes

Soda and carbonated drinks are examples of heterogeneous mixtures even though they are solutions. This is due to the fact that the carbon dioxide bubbles constitute by themselves a gaseous phase or component, visibly recognizable on the surface of the liquid or within it, as in the case of the image above.

Other examples

  • If sand is added to a bottle of water , the mixture would be a liquid-solid heterogeneous mixture or suspension.
  • Vegetable and meat soups or broths .
  • bowl of cereal with milk is a mixed bag. 
  • pizza is heterogeneous. Added toppings such as ham or pineapple are not evenly distributed throughout the pizza, and neither is the cheese and sauce on the pizza. This means that it is a smorgasbord.
  • The mixtures of nuts are heterogeneous mixtures because the constituent elements are different.
  • The ocean is one of the largest heterogeneous mixtures in existence. The sea is a non-uniform distribution of animals, plants, and other essential components that make it heterogeneous.
  • The pollution or contamination is a heterogeneous mixture of various particles suspended in the air.
  • mud puddle is a mixed bag, as it is made up of dirt, grass, leaves, and animal waste mixed in the water.
  • Although vinegar and oil are often mixed as a seasoning, the mixture itself is heterogeneous. They can stay together for a while, but they will always part after a while.
  • The concrete used in construction is a heterogeneous mixture of an aggregate, cement and water .
  • The seasoning salt and pepper form a heterogeneous mixture.
  • The sugar and sand also form a heterogeneous mixture. By mixing and looking closely, small sugar crystals and sand particles can be separately identified.

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