HISTORICAL INFORMATION

Discovered by : Sir Humphrey Davy

Discovered at : England

Discovered when : 1807

Origin of name : From the English word "potash" (pot ashes) and the Arabic word "qali" meaning alkali (the origin of the symbol K comes from the

Latin word "kalium")

POTASSIUM

Symbol : K

Atomic number : 19

Atomic weight : 39,0983

Group number : 1

Group name : alkali metal

Period number : 4

Block : s-block

Standard state : solid at 298 K

Colour : silvery white

Classification : Metallic Density @ 293 K : 0.862 g/cm3

Melting point : 336.53 K (63.38°C)

Boiling point : 1032 K (759°C)

Electronegativity : 0.82 Energy ionization : - 1st ionization energy : 418.8 kJ/mole - 2nd ionization energy : 3051.3 kJ/mole - 3rd ionization energy : 4411.3 kJ/mole Electron affinity : 48.385 kJ/mole Isotope : 39K, 40K, 41KElectron configuration : [Ar] 4s1Structure : body-centered cubic

Isolation

Potassium is not made by the same method as sodium as might have been expected. This is because the potassium metal, once formed by electrolysis of liquid potassium chloride (KCl), is too soluble in the molten salt.cathode: K+(l) + e- K (l)anode : Cl-(l) 1/2Cl2 (g) + e-

Instead, it is made by the reaction of sodium vapor with molten potassium chloride.Na + KCl K + NaCl

This is an equilibrium reaction and under these conditions the potassium is highly volatile and removed from the system in a form relatively free from sodium impurities, allowing the reaction to proceed.

Chemical reactions of the elements

Reaction of potassium with airIf potassium is burned in air, the result is mainly formation of orange potassium superoxide, KO2.K(s) + O2(g) KO2(s)

Reaction of potassium with waterPotassium metal reacts very rapidly with water to form a colourless solution of potassium hydroxide (KOH) and hydrogen gas (H2). The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic. 2K(s) + 2H2O 2KOH(aq) + H2(g)

Reaction of potassium with acidsPotassium metal dissolves readily in dilute sulphuric acid to form solutions containing the aquated K(I) ion together with hydrogen gas, H2.2K(s) + H2SO4(aq) 2K+(aq) + SO4

2-(aq) + H2(g)

Reaction of potassium with the halogensPotassium metal reacts vigorously with all the halogens to form potassium halides. 2K(s) + F2(g) KF(s)2K(s) + Cl2(g) KCl(s)2K(s) + Br2(g) KBr(s)2K(s) + I2(g) KI(s)

Reaction of potassium with basesPotassium metal reacts very rapidly with water to form a colourless basic solution of potassium hydroxide (KOH) and hydrogen gas (H2). The reaction is exothermic. 2K(s) + 2H2O 2KOH(aq) + H2(g)

The picture shows the reaction The picture shows the reaction between potassium metal and between potassium metal and water.water.

Uses

- The superoxide KO2 is used in breathing apparatus where moisture in the breath and carbon dioxide reacts with it to release oxygen

2KO2 + H2O + 2CO2 2KHCO3 + O2

- the alloy of potassium with sodium (NaK) is used as a heat-transfer medium in nuclear reactors.

- Fertilizers usually as the chloride, sulphate, nitrate, or carbonate

possium nitrate, KNO3, and potassium chlorate, KClO3, are used in fireworks

- Potassium permanganate, KMnO4, is an important oxidizing agent

low-sodium salt

- Potassium hydroxide is used in the preparation of potassium phosphates for liquid detergents