POTASSIUM - K
Properties of Potassium :
An alkali metal. A silvery-white (in a thin layer - with a purple tinge), soft, low melting. Blue-green pairs of potassium consist from atoms of K (mainly) and K2 molecules. Chemically dissolves in liquid ammonia (dark blue solution), in the molten hydroxide potassium. It is extremely reactive, the strongest reducing agent, reacts with O2 of air, water (there is ignition of the evolved hydrogen), dilute acids, non-metals, ammonia, hydrogen sulfide. Practically does not react with nitrogen (in contrast to Li and Na). It is well preserved under a layer of gasoline or kerosene. With the mercury forms an amalgam. Do not fused with Li, Mg, Zn, Cd, Al and Ga. Forms intermetallic compounds with Na, Tl, Sn, Pb and Bi. Colors the flame of a gas burner in a purple color. The fifth element of the spread in nature.
| Molar mass | g/mol | 39.098 |
| Density in solid state | g/cm3 | 0.8629 |
| Melting point | °C | 63.51 |
| Boiling point | °C | 760 |
Obtaining metallic potassium:
2 KH = 2K + H2 (400° C, vacuum).
4 KOH (liquid) → Electrolysis 4 K (cathode) + O2 ↑(anode) + 2 H2O.
2 KCl (liquid) → Electrolysis 2 K (cathode) + Cl2 ↑(anode).
2 KCl + 2H2O → Electrolysis H2↑(cathode) + Cl2 ↑(anode) + 2KOH
2 KCl (melt) (on Hg-cathode)→ Electrolysis 2 K(cathode) + Cl2 ↑(anode).
Chemical reactions with metallic potassium:
2 K + 2H2O = 2 KOH + H2↑.
2 K + 2 HCl (diluted) = 2KCl + H2↑.
8 K + 6 H2SO4 (diluted) = 4 K2SO4 + SO2 + S ↓ + 6 H2O (impurityH2S)
21 K + 26 HNO3 (diluted) = 21 KNO3 + NO ↑ + N2O ↑ + N2 ↑ + 13H2O.
2 K + 2 KOH = 2K2O + H2 (450° C).
2 K + H2 = 2 KH (200—350° C).
K + O2 (air) = KO2 (burning, impurity of K2O2)
K →( O2 ) K2O2↓ →O2, (time) KO2↓ (- 50° C, in the liquid NH3).
4 K + O2 + 2 H2O = 4KOH.
2 K + E2 = 2 KE (normal temp.; E = F, Cl, Вr, I).
2 K + E = K2E (100—200°C ;E = S, Se, ТE).
З K + Р (red) = K3P (green) [200° C, in the atmosphere Аr].
2 K + 2 H2S (saturated)= 2 KHS ↓ + H2↑ (in benzene).
2 K + 2 NH3 (gas) = 2KNH2 + H2 (65—105° C).
K + 6 NH3 (liquid) = [K(NH3)6] (dark-blue) [- 50° C]
[K(NH3)6] + n NH3 (liquid) ↔ [K(NH3)6]+ + E-nNH3.
