From weak carbonic acid (it is unstable and can exist only in dilute solutions), when interacting with alkalis, acidic and intermediate salts are obtained, which are otherwise called hydrocarbonates and carbonates, respectively. The reaction equations can be written: H2CO3 + KOH → KHCO3 + H2O and H2CO3 + 2KOH → K2CO3 + 2H2O. In the first, potassium bicarbonate is obtained, and in the second, potassium carbonate. The acid salt formula is KHCO3 and the medium is K2CO3. The molar mass of potassium carbonate is 138.2 g / mol. In appearance, the salt resembles a white crystalline powder, which is not combustible, melts at a temperature of 891 C, without reaching the boiling point, the salt decomposes. Potassium carbonate is hygroscopic, it dissolves well in water: in 100 ml at 20 ° C - 110.5 g, and at 100 ° C - 156 g of salt. But this substance does not dissolve in alcohol or in acetone.
In ancient times, potassium carbonate was called potash, the word comes from the Latin name "potassa". Potassium carbonate is one of the oldest salts that have been known to people since ancient times. In Europe, until the last century, potash was one of the most important chemicals of industrial importance. In Russia, the monopoly was established on the production of potash by Peter the Great in 1721. At present, in the territory of the Russian Federation, as well as in Armenia, Kazakhstan, Belarus, Ukraine, Turkmenistan, Moldova, Uzbekistan, the interstate standard GOST 10690-73 applies to this chemical. Potash refers, according to GOST 12.1.005-88, to substances of the third hazard class, if it comes into contact with mucous membranes or wet skin, it causes irritation.
If potassium carbonate is mixed with water, then a lot of heat is released when it is dissolved, that is, the K2CO3 hydrolysis reaction is exothermic, and new substances are formed under the action of water. The salt of dibasic carbonic acid is hydrolyzed stepwise. First, an acid salt is formed: H2O + K2CO3 → KHCO3 + KOH. Then the second stage of water decomposition of the already acid salt weakly proceeds: H2O + KHCO3 → H2CO3 + KOH. Since the hydrolysis of potassium carbonate, like other salts of weak acids, proceeds with the formation of hydroxyl ions OH-, the pH of their aqueous solutions is always more than 7, and the medium is alkaline.
Potassium carbonate in the 17th century in Russia was obtained by leaching wood ash. An alkali solution was prepared in wooden troughs, pouring ash over hot water. Then this solution was poured into a brick hearth with burning firewood. Potassium carbonate crystallized in a very dense layer at the bottom of the outbreak, with the help of scrap, potash was mined and laid out in barrels, corking them tightly. Certain skill was required so that the solution was evaporated, and the bonfire was not extinguished. Therefore, the craft of "watering" began to be taught in adolescence, and only a few years later the worker acquired certain skills and became a master of his craft. For example: when burning a bonfire, white ash is always formed, its main part is potash. Today, another industrial method is implemented - carbon dioxide is passed through potassium hydroxide obtained by electrolysis: 2KOH + CO2 → K2CO3 + H2O. The result is potash and water.
Potassium carbonate is used in the manufacture of soaps and glass. In the laboratory, it is used as a mild desiccant in cases where other products, such as calcium chloride or magnesium sulfate, are not allowed. It is not suitable for drying acidic compounds, but can be used for drying organic products with a low content of acidic impurities. Potassium carbonate is used to extinguish class B fires , as it relates to chemical powders that can both inhibit and extinguish the combustion process. It has greater fire extinguishing effectiveness than salts such as sodium carbonate, sodium sulfate, sodium fluoride or sodium bicarbonate. Its inhibitory efficiency of combustion processes is also higher than that of sodium carbonate, sodium sulfate, aluminum oxide and calcium carbonate. In the glass industry, K2CO3 is used in the manufacture of laboratory (refractory), optical or potash glass, as well as glass for the manufacture of glassware. In addition, potassium carbonate is in demand in the chemical, agricultural, medical, and food industries.