Potash is the unofficial name for a substance that chemists call potassium carbonate. This salt has been known to people since ancient times, as it is contained in ash. Previously, this word was called the dry residue after evaporation of a solution of plant combustion products. So, what is now known about potash?
Formula
Another name for this substance is potassium carbonate. And its chemical formula is written like this - K 2 CO 3 . It is a medium salt of potassium and carbonic acid. This means that the potash solution is not acidic or basic, it is neutral. For a long time he was confused with baking soda - NaHCO 3 .
History of discovery and study
Of course, we do not know for certain who first got the potash, because it was known in ancient Greece and Rome. Then it was isolated from ash and used for washing. It is curious that for a long time he was confused with another substance - potassium bicarbonate. The baking soda familiar to us, potash - together they were simply called alkaline or alkaline salts. They began to distinguish between the 18th and 19th centuries. For the first time this became known in 1759, when Andreas Marggraf established that soda is a mineral alkali, while potash is a vegetable alkali. And in 1807, Humphrey Davy established the chemical composition of each of these substances.
The first mention of potash production dates back to the 14th century. The largest enterprises were in Germany and the Scandinavian countries. Potassium carbonate was used in soap factories, cloth industry, dyeing enterprises. In the 15th century, Russia also entered the competition. Prior to this, they did not know how to extract potash from ash, but simply exported combustion products along with, for example, furs. The glass industry, both within Russia and abroad, also needed this substance. Demand grew, and supply increased with it.
By the way, the name "potash" is literally a clue to the method of obtaining it in antiquity. The fact is that in Latin it sounds like potassa, which in turn is a merger of the words "ash" and "pot".
Chemical and physical properties
In the course of experiments with this substance, scientists received information about certain qualities inherent in it. Today it is known that under normal conditions, pure potash is a
solid in the form of colorless crystals or white powder. Its density is 2.43 g / cm
3 . The melting point of potassium carbonate is 891 degrees Celsius. It has high hygroscopicity.
This substance is not explosive or fire hazard. Contact with wet skin or mucous membranes causes irritation. Thus, it belongs to the third hazard class.
Varieties and forms
There are two types of potash: calcined and sesquioxide. Unlike the second, the first form does not contain water - in the process of calcination, it
evaporates, and also removes organic matter, as a result, a solution of potassium carbonate of this kind becomes completely colorless.
In addition, potash is distinguished by variety, there are only three. The quality of the final product depends on the content of such impurities as iron, aluminum, chlorides, sodium and sulfate salts. Also, when assigning a variety, the mass fraction of the precipitate deposited in the solution and the loss on ignition are taken into account.
Production
Although the use of potash does not occur on such a large scale as in the case of soda, it is still actively used by people. But first of all, you need to get it. In small quantities, this can be done even at home.
First of all, you need to get at your disposal ash of plant origin. Then you need to dissolve it in a certain amount of hot water, stirring well and wait a while. Next, you need to start evaporating the potash solution with a mixture of organic substances, which will cause crystals to precipitate. Of course, potassium carbonate, isolated in this way, will not be of high quality, and the effort expended is too great in comparison with the amount. So, of course, on an industrial scale, everything happens differently.
So, an aqueous solution of potassium carbonate interacts with CO 2 , which leads to the formation of KHCO 3 . It, in turn, is heated, and water and carbon dioxide are released, while the rest is the original potash.
There are several more ways to obtain this substance, however, the simplest and most effective are those described previously.
Treatment
As already mentioned, there are two types of potash - calcined and sesquioxide. How is the processing of potassium carbonate to obtain a particular variety?
First of all, even their formulas differ. One-and-a-half looks like this: K 2 CO 3 + 1,5H 2 O, that is, it contains water initially. However, it is even more hygroscopic than normal. Anhydrous form can also be obtained from this form - it is enough to heat the powder to 130-160 degrees Celsius.
The calcined form is obtained by processing potassium carbonate obtained by evaporation of a solution of ash in wooden tanks. Such a substance does not
differs in purity, so it must either be calcined or calcined. After one of these procedures, the potassium carbonate powder turns white, and its solution is completely colorless. In this case, the substance does not contain water.
Using
From ancient times to this day, potassium carbonate in various forms is used in a huge number of industries and for a variety of purposes. For example, its excellent cleansing ability is still used in the manufacture of liquid soaps and other household chemicals.
In addition, potash is an antifrosty additive to mortars. As such, it allows mixtures to be more resistant to cold, which makes it possible to continue construction even at fairly low temperatures. Its significant advantage over analogues is that it does not cause corrosion of structures, as well as the formation of efflorescences that could
affect the strength of the structure.
Potassium carbonate is still used in the manufacture of crystal and glass for high-quality optics. There is no substitute for him in this matter. There are no analogues of this substance, for example, in the manufacture of refractory glass.
Often, potash is a component of paints, and also in the chemical industry it is used to absorb hydrogen sulfide from gas mixtures - it copes with this much better than soda. There is a place for him in pharmaceuticals: potassium carbonate is involved in some reactions, and in some places appears as a by-product. Another area of application is fire fighting. It is with this substance that wooden structures are treated, thereby increasing their fire resistance.
Surprisingly, potash is also a nutritional supplement. Its code is E501, so it belongs to class E. For some time it was used in the confectionery business, for example, in the manufacture of gingerbread cookies. In light industry, this substance is also involved in the process of leather dressing.
Finally, there are high prospects for the use of potash in the manufacture of chlorine-free potash fertilizers. Ash has been used in this capacity since ancient times, but in recent decades it has been supplanted by top dressing of industrial production. It is likely that in the near future a method will be applied on a large scale that has been known for a long time and is the least harmful in comparison with the mineral fertilizers used now.
Other features
Since potash is an extremely hygroscopic substance, its packaging, storage and transportation take place under special conditions. As a rule, five-layer bags are used for packing potassium carbonate. This is the only way to avoid unwanted ingress of water into this substance.
In addition, surprisingly, despite the excellent reaction with H 2 O, potassium carbonate is completely insoluble in acetone and ethanol.