Is raw oil a homogeneous mixture

Substances rarely occur in nature as pure substances. Most of the time it is Mixtures of substancesthat are composed of at least two basic substances. Even a highly pure laboratory chemical is never one hundred percent pure; it always contains some impurities, even if only to a small extent. Mixtures of substances can be found everywhere. If you look at a piece of reddish granite, you can see different components: transparent quartz, red and white feldspar, and black mica. If you crush the granite piece with a hammer, you can cut it into its individual components. In the case of granite, the individual components are clearly recognizable. The constituents are all in the solid state, and such a mixture is also called mixture.

If you mix salad oil and water, the oil initially floats on the water due to its lower density. Shake vigorously to partially mix the two liquids. This mixture of two liquids is known as emulsion.  
Milk, too, is an emulsion of fat droplets in water. You can only see under a microscope that there is a mixture of substances in milk. The small dots on the picture show the fat droplets in the milk at a thousandfold magnification:
If you mix a solid substance with a liquid, you get one suspension. When garden soil is stirred in water, the solid components of the soil can be seen even without a microscope. After a while, they settle on the bottom of the vessel and if the constituents of a substance mixture can still be seen with the eyes or with the aid of a microscope, then it is in place heterogeneous mixture of substances in front.

When making a gold bar, you try to use the purest gold possible. The small gold bars on the picture below have a purity of 999.9. That means they contain at least 99.99% gold by mass. The gold ring with the inside stamp 585 contains a guaranteed gold content of 58.5% gold, the remainder is made up of silver, copper or platinum. Here, too, there is a mixture of substances in the form of an alloy. As alloy This is a mixture of substances in which at least one component consists of a metal. The golden yellow brass, for example, does not contain gold, but the brass alloy is made up of the components copper and zinc. Bronze would be an alloy of copper and tin.

However, the individual components of an alloy can no longer be seen even with a microscope. Such mixtures of substances are called homogeneous mixtures of substances. Not only do alloys form homogeneous mixtures of substances, but also solutions and mixtures of different gases. When you sprinkle table salt in water, the salt gradually dissolves and can no longer be seen after a while. You can easily determine with the taste test that it is still dissolved in the water.

Other salts such as potassium permanganate dissolve to form a colored solution. If you carefully layer water over the potassium permanganate, you first get the separated components. But even if the vessel is completely still afterwards, the two components will gradually mix. The phenomenon is explained by the fact that the atoms contained are constantly in motion and thereby mix the components. This mixing, which is caused by the proper movement of the atoms, is called diffusion.

Sometimes heating takes place during the dissolution process, in rare cases even cooling, for example when dissolving potassium nitrate in water. solutions can be found not only in mixtures of a liquid with a solid, but also in mixtures of gases or other liquids with a liquid. Wine is a solution of alcohol in water, as well as other dissolved components, for example sugar or flavorings. If ordinary water is heated in a glass vessel, small gas bubbles rise first: When heated, the dissolved oxygen is first expelled from the water in small bubbles before the larger water vapor bubbles rise (> experiment).

When water is heated, dissolved oxygen is expelled first (top left),
only then does the evaporation process of the water begin (lower pictures)

Ordinary breathing air is an example of a homogeneous mixture of substances between several gases. Its main constituent is 78% by volume of nitrogen, 21% by volume of oxygen and 1% by volume of other gases such as argon or carbon dioxide.

The substance mixtures can be summarized in a table according to the physical state of the components. Heterogeneous mixtures of substances are marked in blue in the table, homogeneous mixtures of substances in orange.

Mixture of substancesfirmlyliquidgaseous
in firmAlloy (brass)
Mixture (granite)
Heap of gravel
spongeRigid foam
in liquidSolution (saline solution)
Suspension (sludge)
Solution (wine)
Emulsion (milk)
Solution (mineral water)
in gaseous formSmokefogGas mixture (air)

Mix fabrics

The mixing of substances in the laboratory or in industry takes place, for example, by shaking, mixing, rolling, kneading, emulsifying (adding an emulsifier in the production of a skin cream), suspending or dissolving. Mixing is accelerated by crushing, stirring or heating. The occurrence of an undesired chemical reaction can be prevented with cooling and with an exact temperature measurement. The substance portions of the components to be used can be determined by weighing or by volume measurements.

Separate substances

According to the general definition, when the substances involved are mixed, no chemical reaction takes place. Nevertheless, physical properties - for example density or boiling points - can be specified for the mixtures. The substance mixtures can be broken down into their components using physical separation processes. In drinking water purification, unwanted components are eliminated through the separation of substances. In the chemical laboratory, the various separation processes are among the most important basic chemical operations. The mixtures are separated based on the different chemical and physical properties of the components involved:  
  • By type of composition: When sorting, the components can be separated based on their different composition. Waste separation is an example of this.
  • According to density: When slurrying, sedimenting, decanting and centrifuging, the components are separated due to their different densities. Example: When pouring the coffee from the coffee grounds in the household, the force of gravity and the higher density of the coffee grounds that settle down are used to pour off the coffee standing above.
  • According to the particle size: When sieving, the particles of the coarser component are retained in the sieve. When filtering a suspension, the solid component remains in the filter paper.
  • According to magnetisability: During magnet separation, magnetisable components are pulled out with an (electro) magnet.
  • After the boiling point: During distillation, liquids are separated from one another by heating. The component with the lower boiling point evaporates first and then condenses in a cooler.
  • After the sublimation point: If you have a mixture of substances in which one of the substances sublimates, this substance can be separated by sublimation.
  • According to the effectiveness of the surface forces: During adsorption, a gaseous or liquid component is held in place by the surface force of another substance - for example activated carbon.
  • According to the crystallization behavior: During recrystallization, a contaminated substance is dissolved and crystallized out again. The impurities remain in the supernatant solution.
  • Due to the solution behavior of the components in a liquid: During extraction, a substance is separated from a liquid, from a solid mixture or from a gas mixture with a liquid solvent.
  • Due to the dissolving behavior of a gas component: During absorption, gaseous impurities dissolve in a liquid (detergent) or in a solid.
  • Due to contamination by water: During thermal drying, the mixture of substances is heated or left in the air. In the first case the water evaporates in the second case it evaporates. In chemical drying, an added substance reacts with the water and thereby removes the water from the mixture.
  • Separation due to different interactions (solubility or adsorption) of the components with an added phase: chromatography.