Potassium (K) is the fifth most abundant metal in nature. It is located in group 1 of the periodic system of chemical elements (PSChE), therefore it belongs to alkali metals and forms soluble hydroxides when mixed with water. In the form of a simple substance, the element has a silver-white color, sometimes with a purple tint. According to its characteristics, it is soft and low melting. Obtaining potassium is possible from its hydride, hydroxide, chloride, chromate or dichromate.
general characteristics
When potassium is converted into blue-green vapor, it decomposes into K atoms, to which a small amount of K 2 molecules are mixed. The metal can be dissolved in liquid ammonia to obtain a standard dark blue solution or in a potassium hydroxide melt.
Potassium has a high reactivity, has strong reducing properties (its outer electron shell is located far from the nucleus, and in the table of electronegativity it takes the second position after cesium), it reacts not only with dilute acids, non-metals, hydrogen nitrite and dihydrosulfide, but also with oxygen and water. In the latter case, the hydrogen released quickly ignites.
With mercury, the element turns into an alloy - an amalgam. With sodium, thallium, tin, lead and bismuth, potassium forms intermetallic compounds with high hardness and chemical resistance. The chemical compound of several metals melts at a higher temperature than each of its constituent components, but has less ductility compared to them.
However, there are substances with which the element practically does not react, for example, nitrogen belongs to such. This is one of the distinguishing features of potassium from other alkali metals, primarily lithium and sodium. In addition, it is not fused with lithium, magnesium, zinc, cadmium, aluminum and gallium.
Potassium is well preserved under a layer of gasoline and kerosene. You can determine it by coloring the burner flame in purple.
Application
Potassium plays an important biological role in the human body and plant development. In addition, it is widely used in everyday life. So, in combination with nitrogen and phosphorus, it is an indispensable fertilizer for cultivated plants, allowing them to increase their productivity, vegetative mass and resistance to pests.
A metal alloy with sodium is used to transfer thermal energy in closed systems, and if cesium is added to this compound, a composition with a record low melting point (minus 78 degrees Celsius) is obtained.
In order to use all these useful and important compounds, one needs to know the reactions for producing potassium from its compounds.
Metal production
A white inorganic compound, potassium hydride, is formed from molten metal, but it is unstable and at a temperature of 400 degrees Celsius in vacuum breaks up into components by the following reaction:
Potassium hydroxide is formed from the corresponding chloride. It is widely used in the production of liquid soaps and for the production of potassium and its compounds. For this, it is necessary to conduct electrolysis, that is, to pass current through the solution. As a result, oxygen is formed at the anode, and potassium at the cathode:
- 4KOH = 4K + O 2 + 2H 2 O.
Not only hydroxide can be obtained from chloride, but also pure metal. This will also require a solution electrolysis reaction:
Unlike the previous method for producing potassium, in this one can use the starting material not only in a liquid state, but also in the form of a melt, but in this case two parallel reactions occur:
- 2KCl + 2H 2 O = H 2 + Cl 2 + 2KOH;
- 2KCl = 2K + Cl 2 .
The cathode on which potassium will be formed must be mercury.
Preparation of starting materials
Chromate or potassium dichromate is sometimes used. Direct metal cannot be obtained from them, but they can be converted to hydroxides or chlorides, which can subsequently be electrolyzed by the above reactions. Obtaining potassium hydroxide from chromate occurs as follows:
- 2K 2 CrO 4 + 2H 2 O + 3H 2 S = 2Cr (OH) 3 + 3S + 4KOH.
In order for the process to be successful, sulfur and chromium hydroxide precipitated; you need to take hot water. A similar reaction can also be carried out using dichromate. It proceeds in a similar way, the difference is observed only in the values of stoichiometric coefficients:
- K 2 Cr 2 7 + 2 + 3 2 S = 2Cr () 3 + 3S + 2KOH.
When dichromate is heated to 500 degrees Celsius, hydroxide can be obtained in another way:
- K 2 Cr 2 O 7 + 3H 2 = Cr 2 O 3 + 2KOH + 2H 2 O.
There are other methods for producing hydroxide. For example, using the reaction between potash and a saturated solution of slaked lime.
To obtain potassium chloride from chromate, reactions are carried out as follows:
- 2K 2 CrO 4 + 2HCl = K 2 Cr 2 O 7 + 2KCl + H 2 O.
Hydrochloric acid is taken in diluted form. The production of potassium chlorine is accompanied by the release of dichromate and water.
Turning dichromate into chloride is a little more difficult, for this you will need ethyl alcohol and boiling:
- K 2 Cr 2 7 + 8HCl + 2 2 5 = 2CrCl 3 + 3 3 () + 7 2 + 2KCl.
Obtaining potassium chlorine is also possible from potash in the interaction with dilute hydrochloric acid and from sulfate in reactions with barium halide.
Hydroxide and chloride are easily converted into each other by electrolysis or by adding the corresponding halide.
Derivatives
Obtaining potassium salts plays no less important role than the formation of pure metal. Despite the high cost, they are used in electroplating, as they provide intensive operation of electrolytes at high current density. This is achieved due to the high solubility.
Potassium nitrate
Of great importance is the preparation of potassium nitrate (KNO 3 ). This white salt, called Indian nitrate, is practically non-toxic to living organisms. It is used both for peaceful purposes as fertilizer and in the military as a component of explosives and combustible substances. In addition, the production of potassium nitrate is necessary for bleaching and improving the strength characteristics of crystal glasses, which is widely used in the vacuum electrical industry and optical glassmaking. In metallurgy, its oxidizing properties with respect to nickel and other ores are useful. And in the food industry, salt acts as a preservative.
To obtain a solution of potassium nitrate, you can use the following substances:
- metal peroxide when nitric oxide (IV) is added to it and heated to 70 degrees Celsius;
- hydroxide and diluted nitric acid;
- cold hydroxide and a mixture of nitrogen oxides (II) and (IV);
- hot hydroxide, nitric oxide (IV) and oxygen;
- hot diluted potassium nitrite and oxygen (reaction takes time);
- potassium nitrite and hot hydrogen peroxide in dilute sulfuric acid as a catalyst (the acid can be replaced with bromine, but it will react with the formation of hydrogen bromide).
The resulting compound melts without decomposition, is stable in air, soluble in water without hydrolysis, has strong oxidizing properties, and is reduced only by atomic hydrogen.
Potassium sulfate
Salt, known since the XIV century, was called potassium sulfate (K 2 SO 4 ) only in the XVII. It is present in the waters of salt lakes and deposits of non-metallic mineral resources, but it is possible to obtain potassium sulfate in the synthesis of the following substances:
- potassium and sulfur peroxide at 130-140 degrees Celsius (instead of sulfur, you can use its oxide (IV), then a temperature of 100 degrees will be enough);
- potassium hydroxide and dilute sulfuric acid;
- potassium hydrosulfate (decomposition at 240 degrees);
- potassium hydrogen sulfate and concentrated caustic potash or chloride of the same metal;
- potassium chloride and concentrated sulfuric acid by boiling;
- potassium sulfide and oxygen at temperatures above 500 degrees;
- decomposition of potassium disulfate at temperatures above 440 degrees and the use of sulfur oxide (IV) and oxygen as catalysts.
Another name for the resulting substance is arcanite. It has a white color, is resistant to temperature effects, but is easily soluble in water without crystalline hydrates. It is characterized by participation in metabolic reactions, reduction with hydrogen and carbon.
In practice, it is actively used in agriculture as a chlorine-free fertilizer for potassium-poor soils. Arcanite is especially important for crops that are sensitive to chlorine or consume a lot of sulfur. A crop grown with its use contains more sugar and vitamins than one that did not fertilize. Also, fertilizer is used for flowers grown both outdoors and in greenhouse conditions.
Another application of arcanite is a component in the production of glass, alum, and metallurgical floods. It also acts as a nutritional supplement, but the substance itself can hardly be called safe: it irritates the eyes, skin, gastrointestinal tract, respiratory tract and leads to poisoning with prolonged contact with various parts of the body and body.
Potassium carbonate
Potash or potassium carbonate (K 2 CO 3 ) was known in antiquity and retained important industrial value until the twentieth century. Potassium carbonate was obtained by leaching from vegetable ash and subsequent purification of the product. Basically, production was localized in the wooded area of Europe, Russia and North America.
More reactions are now known that produce carbonate. The following substances are commonly used:
- potassium superoxide and graphite with slight heating up to 30 degrees (carbon monoxide can be used instead of graphite with heating up to 50 degrees);
- concentrated potassium hydroxide and carbon dioxide;
- decomposition of potassium bicarbonate at a temperature of from 100 to 400 degrees;
- bicarbonate and concentrated potassium hydroxide;
- potassium sulfate, calcium hydroxide and carbon monoxide at a temperature of 200 degrees and under pressure, followed by synthesis of the resulting product K (NSOO) with oxygen at 700 degrees.
The resulting white substance melts without decomposition, is strongly hydrolyzed in water by the anion, creates a highly alkaline environment, reacts with acids, non-metals and their oxides, and also enters into metabolic reactions.
The substance is low toxic and is used to produce liquid soap, pigments, glass, potassium compounds. It is used in dyeing, growing crops, developing photographs. In addition, it is a popular additive that reduces the freezing point of concrete, a hydrogen sulfide scavenger, a dehydrating agent, and a food additive.
Potassium permanganate
Red-violet, almost black potassium permanganate is known to everyone, since it can be seen in almost every house. Although in recent years there have been small restrictions on the purchase of a substance due to the fact that it was recognized as a precursor. Obtaining potassium permanganate (KMnO 4 ) is possible in several ways, for example, by the interaction of manganese (II) sulfate with water and oxygen from potassium dithionate. After some time, in the presence of silver nitrate as a catalyst, permanganate and potassium sulfate, as well as sulfuric acid, will be obtained from this mixture.
Even more methods involve the use of potassium manganate, the following substances can be added to it:
- water (reaction takes time);
- dilute hydrochloric acid;
- carbon dioxide;
- chlorine.
In addition, manganate can be electrolyzed to form permanganate at the anode (there will be hydrogen at the cathode).
The use of the resulting substance is wide. Due to its oxidizing ability, it provides an antiseptic effect. In medicine, it is used to gargle with inflammatory diseases of its mucous membrane, rinse wounds, treat burns and infected wounds, treat ulcers, and also as an emetic for alkaloids poisoning.
Hypersensitivity is a contraindication, but an overdose can lead to death even in a healthy person, the lethal dose for the average person is only 20-30 g.
When using permanganate, safety precautions must be observed, so the substance ignites when mixed with organic and flammable compounds, active metals and non-metals. With additional heating, explosion is possible.
Potassium hydroxide
In addition to salts, potassium hydroxide is of great importance. This substance belongs to alkalis, that is, substances whose solutions and melts can conduct an electric current.
The trivial name for this compound is caustic potash. It looks like a white hygroscopic substance. Its properties include melting and boiling without decomposition, good solubility in water with the formation of a highly alkaline medium, neutralization with acids, reactivity with respect to metals and non-metals, their oxides and hydroxides. Potassium hydroxide actively absorbs water and carbon dioxide from the air.
As potassium production is possible from alkali, hydroxide can also be obtained from metal. To do this, you only need to add water to it in pure form or in combination with oxygen. In addition, you can get alkali from carbonate and saturated calcium hydroxide or by electrolysis of chloride. The latter method is actively used in industrial production.
The substance is dangerous, can burn skin or mucous membranes, destroys all materials of organic origin. You can work with it only by reliably protecting the skin with gloves and eyes with glasses.
Despite the danger, alkali is widely used in photography, oil refining, food, paper and metallurgical industries, as well as an alkaline battery, acid neutralizer, catalyst, gas scrubber, pH regulator, electrolyte, component of detergents, drilling fluids, dyes, fertilizers , potassium organic and inorganic substances, pesticides, pharmaceuticals for the treatment of warts, soap, synthetic rubber.
Thus, the production of potassium and compounds based on it, primarily salts and hydroxide, is of great importance for industry and widespread use in everyday life. The main thing is to remember the safety precautions when working with this alkali metal and carefully use the materials in which it is used. Thanks to this, it will be possible to avoid those properties that are dangerous.