We explain what mixtures are and what their general characteristics are. We also explain the types of mixtures that exist and some examples.
What are mixtures?
There is talk of mixing when two or more substances are combined without being joined by chemical bonds. In everyday life mixtures surround us, for example, many biological fluids, such as blood, are mixtures from a chemical point of view.
It may be useful for you: Colloids
Methods of separating mixtures
A mixture can be defined as such only when the individual substances can be obtained again by applying physical separation procedures. If the mixture generates some type of chemical reaction, then physical separation mechanisms cannot be used. The most widely used physical methods for separating mixtures are filtration, decantation and distillation.
- Filtration. It is used to separate small particles of solids suspended in liquids. A porous system, for example a sieve, is used to separate the components, so solid particles larger than the holes in the sieve are trapped in it, while the liquid flows through the holes.
- Decantation. It is used to separate suspended solids in liquids and also immiscible liquids (which do not dissolve in each other). The separation is based on the difference in density of the components of the mixture. A separatory funnel is usually used.
- Distillation. It is used to separate mixtures of liquids. The separation is achieved by differences in boiling points: the liquid that has a lower boiling point passes to the vapor phase, is then condensed (using condensers) and is then collected in another container. The liquid that has the highest boiling point remains in the original container where the mixture was.
More in: Separation of mixtures
Characteristics of mixtures
- Its components can be separatedMixtures are generated by the combination of substances under certain conditions (heat, pressure, etc.). Therefore, they can also be separated into their individual components and recovered by applying physical separation procedures, such as filtration or centrifugation (a method of separating solids mixed with liquids using rotating force).
- They have variable compositionsThis is especially true in the case of mixtures that occur in nature, such as air, soil or sea water, which may at a given time have a higher concentration of salts, nitrogen, suspended solids, etc.
- They do not form chemical bonds. It should be clear that a mixture is not a chemical substance, which means that it does not originate as a result of chemical reactions. This is why there is no net energy change in the mixing process, although in some solutions there is a release of heat, which can be very intense (as when trying to make a solution of sulfuric acid or sodium hydroxide). .
- They can be radioactive. Some mixtures can be reactive under certain conditions. For example, in an internal combustion engine, gasoline or diesel is mixed with air and this initiates the ignition of the engine.
- They do not have a chemical formula. They cannot be represented by a chemical formula. As they are not composed of defined proportions of the elements that make them up, mixtures cannot be expressed by a formula, as is the case with substances of known composition.
- They can have one or more phases. In many mixtures there are at least two phases that can be distinguished from each other, one is called the dispersed phase and the other is called the dispersing phase. The dispersant is the predominant phase within which the dispersed phase is located. On the other hand, some mixtures, such as solutions, have only one phase.
- Some physical-chemical properties of the dispersing phase may varyThe substances that make up the mixture retain their chemical nature, but some physical-chemical properties of the dispersing phase may vary due to the presence of the dispersed phase. For example, the boiling point of water increases and its freezing point decreases when a solute is added. This phenomenon is known as “cryoscopic descent” and it is important to take it into account in the manufacture of various products.
Types of mixtures
The two main types of mixtures are:
- Homogeneous mixturesTheir components cannot be distinguished either by the naked eye or by using a magnifying glass or microscope, as they are integrated in a completely uniform manner. They can be liquid, gaseous or solid, the final state generally depends on the solvent. The most common homogeneous mixtures are solutions of solids in liquids or solids in solids, such as the alloys used in metallurgy.
- heterogeneous mixturesThey present discontinuities and often this results in the formation of phases that are clearly distinguishable to the naked eye.
Examples of mixtures
Some homogeneous mixtures:
- Commercial bleach, which can have varying concentrations of sodium hypochlorite (NaClO).
- A coffee with milk
- A brine
- Tincture of iodine
- Some metal alloys (steel, iron-carbon alloy)
- sugar in water
Some heterogeneous mixtures:
- The blood
- Soil
- sand in water
- Oil and vinegar
- The cement
It may help you: Aggregation states