Separating heterogeneous mixtures between solids
collection
Before cooking rice, beans, lentils or peas, the housewife or cook usually “chooses” these foods, separating small stones and other residues that may be mixed with other grains.
Thus these elements can be separated from each other manually.
The manual separation process of the different components (or phases) that make up a mixture is called scavenging.
Levigation
When a mixture is formed by solid substances of different densities, a stream of water can be used to separate them.
This is the case with gold, which is usually found next to a portion of land or sand.
To separate these substances, the mixture is crushed in a specific container and a stream of water is passed through it. The less dense part (the sand or earth) is carried by the water, while the denser part (the gold) is deposited at the bottom.
This process of separating denser elements from less dense elements using running water is levigation.
Flotation
There is another way to separate solids of different densities using water. But in this case, running water is not used.
To separate a mixture of sand and sawdust, for example, just place the mixture in a bowl and add water. The less dense part of the mixture (the sawdust) floats, while the denser part (the sand) is at the bottom of the bowl.
This process is called flotation.
Flotation is often employed in mining to separate ores from their impurities. In this case, proceed as follows: crush the rock and add oil. The ore particles will settle in the oil. By adding water to the set, the particles fixed in the oil go to the surface and the impurities remain at the bottom of the vessel.
screening
When preparing a cake, bakers usually sift the flour and baking powder. In this way, the good flour is separated from the lumpy one. The finer part (the good flour) passes through the sieve meshes. The lumps are retained in the sieve.
In laboratories, very fine sieves called sieves are used. Therefore, the process of separating mixtures through sieves is called screening.
magnetization
You can even imagine how to separate a mixture of solids containing iron, right? And just get a magnet.
A mixture of iron filings and another substance – sulfur powder, for example – can be separated using a magnet. Bringing the magnet close to the mixture, the iron filings stick to it, separating from the sulfur.
Ventilation
Do you know the rice processing machine? She separates the husk from the grain as if she were blowing. The rice husk is less dense than the rest of the grain and is carried along with the air current.
Ventilation is the method of separating solid substances of very different densities by means of an air stream.
fractional dissolution
How to separate salt from a portion of sea sand?
In this case, it is about two solids. If we add water to this mixture, the water will evaporate, leaving only the salt in a solid state separated from the sand.
Separating heterogeneous mixtures into solids and liquids:
Filtration
By the name itself, you can already imagine how the filtration process is carried out: through a filter, which retains the solid part and lets the liquid part pass.
There are several types of filters: cotton, paper, porcelain, etc.
Decantation
There are mixtures that, if left to rest for a while, have their solid part deposited at the bottom of the container. This can be seen in a mixture of water with sand or clay, for example. You can do this experiment yourself, without difficulty.
After the solid part has settled to the bottom of the container, we can pour out the liquid part.
Centrifugation
If we want to quickly separate a solid from a liquid, we can “accelerate” the decantation. For this, the mixture is placed in a device called a centrifuge, which rotates at high speed, depositing the solid particles, which are dense, at the bottom.
Nowadays, this process can be observed even at home. Washing machines, for example, have a centrifuge device, which is activated when you want to «wring» the clothes. Spinning at high speed, the clothes are thrown against the wall, while much of the water is extracted from the clothes.
The centrifuge is also used in clinical analysis laboratories to separate blood components.
Siphoning
After decantation, if it is not possible to overturn the container to empty the liquid, it can be removed with a siphon. A siphon is a specially shaped pipe, usually made of plastic or glass, used to drain water from one container to another.
It is important to note that the original container (A) must be on a higher level than the other one (B). And also that the siphon must be full of water to start the operation, since it is necessary that a continuous flow of water form from A to B.
You can then proceed as follows: dip one end of the tube into the liquid in container A, place your mouth on the other end and aspirate, pulling the liquid, causing it to start flowing from A to B.
The siphon is also used to separate liquids that do not mix, such as water and oil.
Separating homogeneous mixtures:
Evaporation
We have already seen this process briefly in the section on fractional dissolution. It is a process used to separate a solid from a liquid (such as water, for example). The mixture is heated and, as the temperature increases, the water evaporates and the solid remains in the container.
Evaporation can also occur when the mixture is exposed to air, as the liquid part evaporates at room temperature; what remains is the solid part. This type of fractionation is carried out in salt pans, places where salt is removed from sea water.
Distillation
It is the process by which we can separate a liquid mixed with another liquid or a solid. This is done by vaporizing the liquid and then condensing it. It is a process widely used in laboratories and industries, such as beverage and medicine.
Distillation is done in a device called a distiller.
Let’s imagine a solution composed of a liquid and a solid. The solution is placed in a glass flask that receives heat from a source. As soon as the solution begins to boil, steam rises and passes into the condenser. There the steam is cooled to return to its liquid state, that is, to condense. The solid substance remains in the balloon.
The condenser is kept cold through a tube that supplies it with cold water. Otherwise, the vapors are not cooled and do not condense and do not pass to the other flask.
The distilled liquid falls into the other flask in the form of drops.
fractional distillation
The fractional distillation process involves heating a mixture of more than two liquids that have boiling points that are not very close.
Thus, the solution is heated and, initially, the liquid with the lowest boiling point is separated.
Then, the solution is heated until the liquid with a boiling point above the first liquid separated is separated, and so on until the liquid with the highest boiling point is separated.
Fractional distillation is used, for example, in petrochemical industries to separate the various petroleum derivatives.
fractional merger
How can we separate a mixture of solids? Iron, lead and tin, for example.
Knowing the melting point of each of the solid substances, it is relatively easy to separate them.
Tin melts at 231°C; lead, at 327ºC; iron at 1,536°C. We can melt (melt) tin first, then lead, and finally iron. Each element, when melted, is separated from the others.
fractional solidification
Did you realize how important it is to know the physical properties of a substance? Boiling and melting points are important for separating substances. The freezing point is also useful for separating the components of a mixture.
Fractional solidification can, for example, be used to separate paraffin from other petroleum residues. In this case, the mixture is cooled down to the paraffin solidification point. Thus, hardened, the paraffin is removed from the mixture.