|Name: potassium||Group number: 1|
|Symbol: K||Group name: Alkali metal|
|Atomic number: 19||Period number: 4|
|Atomic weight: 39.0983 (1)||Block: s-block|
|CAS Registry ID: 7440-09-7||Voice: |
|Standard state: solid at 298 K||Colour: silvery white|
|Classification: Metallic||Availability: |
Nearing Zero cartoon included by kind permission of Nick Kim.
IsolationHere is a brief summary of the isolation of potassium.
Potassium would not normally be made in the laboratory as it is so readily available commercially. All syntheses require an electrolytic step as it is so difficult to add an electron to the poorly electronegative potassium ion K+.
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 metallic sodium with molten potassium chloride at 850°C.
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.