Potassium. Properties and application
Potassium is a chemical element from the group of alkali metals in group 1 of the periodic table and atomic number 19. It is a soft metal that can be cut with a knife like cheese. What properties does it have? What is the use of potassium?
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1. Discovery of potassium
Already in antiquity, potassium compounds were known in the form of a product obtained by leaching wood ash with water, evaporating the solution and roasting what was left.
Arabs and medieval alchemists converted potash (the impure form of potassium carbonate) into caustic potash using the calcium base:
K2CO3 + Ca (OH) 2 → 2KOH + CaCO3 ↓
Potassium was discovered and extracted in 1807 by the British chemist and physicist Sir Humphry Davy "ego" through the electrolysis of potassium hydroxide. The Polish name "potassium" was first proposed by Filip Walter.
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2. Characteristics of potassium
Potassium (K) is a chemical element with atomic number 19. It is in group 1 (IA) of the periodic table of elements - in the group of alkali metals. The atoms of the elements in this group have one normal state valence electron on the s orbital. This electron is weakly bound, as evidenced by the low value of the first ionization energy.
The low ionization energy and large atomic radius are associated with a low electronegativity value. Lithiums easily donate electrons and turn into an ionic state, which is also visible in the strongly negative normal potentials of these metals.
3. Chemical and physical properties of potassium
Potassium is a very soft metal and one of the lightest. It can be easily cut with a knife, and just after cutting it has a silvery-white color. It is a very active element, its standard potential of the K + / K system is -2.93 V.
Potassium vapors color the flame purple, which can be seen through cobalt glass. It can ignite and explode on contact with water and acids. It reacts with alcohols, displacing hydrogen from them and thus forming alcoholates.
Potassium has strong reducing properties. It reacts directly with hydrogen to form potassium hydride, and with sulfur and halogens. Reacts violently with water, releasing hydrogen and strong base:
K + H2O → 2KOH + H2 ↑
Burned in excess of oxygen, it forms a yellow-colored potassium monoxide, K2O. At a temperature of about 20 ° C, in air, it is covered with a layer of K2O. If its surface is not passivated, it can catch fire in the air.
Dissolves violently in acids, forming salts with evolution of hydrogen. We store it in paraffin oil or kerosene (preferably under a layer of argon).
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4. Obtaining potassium
We obtain metallic potassium as a result of:
- action of sodium on liquid KOH or KCl;
- electrolysis of molten hydroxides or molten anhydrous salts (usually chlorides);
- calcination of carbide (calcium carbide) with potassium fluoride.
Of the alkali metals, only sodium is produced on an industrial scale.
5. The use of potassium
Due to the high reactivity of potassium and its high price, the use of potassium is very limited. In the liquid state, it is used as a cooling liquid in nuclear reactors, as well as in organic syntheses as a reducing agent.
The 40K radioactive isotope has been used in biological and chemical research.
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Potassium nitrate is a valuable mineral fertilizer as well as a component of gunpowder. Potassium hydroxide is used as an agent for the production of soft soaps and for drying.
Potassium chloride is the basic raw material for the preparation of other potassium compounds. It can also be used as a mineral fertilizer.
Potassium carbonate is used in the soap industry and dyeing. It is also used in the production of non-fusing potassium glass.
Potassium hydrogen sulphate, when heated, turns into metabisulphate, which is a great solvent for heavy metals.