Potassium

Potassium, K, is an Alkali Metal element, found in Group Ia of the periodic table.

Atomic Number : 19
Relative Atomic Mass : 39.10

Three isotopes are known with mass number 39, 40 and 41. The radioactivity is due to the isotope of mass 40, which is present to the extent of 0.012%.

Discovery

Potassium metal was first isolated by Sir Humphery Davy in 1807AD by the electrolysis of fused potassium hydroxide.

Occurrence

Potassium is an abundant metallic element which is widely distributed. However, because of its high reactivity is not found naturally in its elemental state. Further, potassium compounds do not occur in workable deposits and are not found concentrated in one location.

Extraction

Potassium metal is prepared by heating potassium carbonate with charcoal.


		2 C   + KCO3   ==>   2 K   +  3 CO2

Preparation

Properties

Potassium metal is

a soft silvery-white lustrous metal, which can be easily cut with a knife.
is highly reactive which tarnishes readily in air due to the formation of a layer of potassium oxide on the surface of the metal.
```
		4 K   +   O2   ==>   2 K2O   	
```
feebly radioactive, emitting beta-rays.

Reactions

Its chemical properties resemble those of sodium, but its reactions are somewhat more vigorous. Potassium metal

is highly reactive chemically, and must be stored under liquid paraffin which contains no oxygen to prevent oxidation,
burns readily in air forming potassium dioxide,
```
		K   +   O2   ==>    KO2   	
```
reacts readily with the halogens, forming the appropriate potassium salt,
```
		2 K   +   Cl2   ==>   2 KCl   	
```
reacts violently with water forming potassium hydroxide and liberating hydrogen. The heat evolved in the reaction is sufficient to ignite the hydrogen liberated.
```
	   2 K   +   2 H2O   ==>   2 KOH   +   H2	
```

Uses

Potassium is used in organic chemistry as a powerful Reducing Agent.

Detection and Analysis

Potassium is detected in its compounds by the characteristic lilac colouration which it imparts to flames when burned and by spectroscopic methods.

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