Potassium catches fire on reaction with water
Potassium and its compounds emit a lilac color in a flame test.
Potassium is an alkali IA group metal, it is not found in it's free state. In combined state, potassium compounds are widely distributed in nature almost to the same extent of sodium compounds. All plants contain considerable amount of potassium compounds which they receive from soil. Its compounds occur as salt beds, in rocks and sea water. The important minerals of potassium are Sylvite (KCl) Sylvinite (NaCl.KCl), Carnallite (KCl.MgCl2.6H20).
Potassium is a highly reactive metal,it oxidizes to potassium peroxide on exposure to oxygen. Potassium on reaction with water catches fire due to its exothermic character and release of hydrogen gas during the reaction.
Potassium chloride (KCl) and Potassium hydroxide (KOH) are two important compounds of potassium.
Sylvine
Potassium Chloride (KCl)
Commercially, potassium chloride is called muriate of potash. It occurs in the Stassfurt deposits as Sylvine (KCl. NaCl), and as Carnallite (KCl.MgCl2.6H2O).
Preparation of potassium chloride:
From Carnallite:
Powdered carnallite is extracted with hot 20% solution of magnesium chloride. The solution is filtered to remove insoluble NaCl and MgSO4, and left for crystallization. Cubic crystals of potassium chloride separate out, leaving behind magnesium chloride in the mother liquor. Potassium chloride so obtained is not highly pure, and used as a fertilizer under the name muriate of potash. The mother liquor left behind is recycled to dissolve more carnallite.
From Sylvine:
Sylvine is a mixture of sodium and potassium chlorides. A boiling hot saturated aqueous solution of sylvine is cooled when crystals of potassium chloride separate out.
Properties: Potassium chloride is a white crystalline solid (m.p = 768 °C; b.p = 1411°C). KCl is an ionic compound. It is fairly soluble in water. In aqueous solution, it gets split into ions (K+ and Cl–) almost completely.
Crystalline Potassium Chloride
Uses of KCl
- As a fertilizer.
- As a starting material for preparing other potassium salts.
- In the pure form, it is used by persons having high blood pressure as a substitute for sodium chloride.
Potassium hydroxide pellets
Potassium Hydroxide, (KOH)
Preparation:
Potassium hydroxide is prepared by the electrolysis of a solution of potassium chloride in an electrolytic cell.
At cathode:
At anode:
Potassium liberated at mercury cathode forms amalgam with mercury. Potassium amalgam when treated with a calculated amount of water gives KOH of the desired concentration.
Properties:
Potassium hydroxide is a white, highly deliquescent solid which melts at 633 K (360°C).
Potassium hydroxide is highly soluble in water, (112g/100 g) as well as in alcohol, (33g /100g)
It shows all the characteristics of a strong alkali. It absorbs carbon dioxide from the air to give potassium carbonate (K2CO3).
Uses
- It is used as an electrolyte in alkaline batteries due to its conductive nature in its aqueous state.
- Potassium hydroxide is used in the manufacture of soft toilet soaps and in production of bio-diesel.
- Also used in preparation of other potassium compounds such as potassium carbonate, potassium cyanide, potassium permanganate,potassium phosphate etc..,
- KOH is an important laboratory reagent. For example, an alcoholic solution of KOH, i.e., alcoholic caustic potash is used in many organic reactions.
- An aqueous solution of KOH is used for absorbing carbon dioxide.