Oxides of Alkali Metal

The possible oxides of Na are Na₂O and Na₂O₂.

It is obtained by burning sodium at 180^o C in a limited supply of air or oxygen and distilling off the excess of sodium in vacuum, or by heating sodium peroxide(Na₂O₂), nitrate(NaNO₃) with sodium

2Na + 1/2O₂ → Na₂O

Na₂O₂ + 2Na → 2Na₂O

2NaNO₃ + 10 Na → 6Na₂O + N₂

It dissolves in water violently yielding caustic soda.

Na₂O + H₂O → 2NaOH

Sodium Peroxide (Na₂O₂)

It is formed by heating the sodium metal in excess air or oxygen. The air should be moisture free and temperature required is 300^o C.

2Na + O₂ → Na₂O₂

(i) It is pale yellow solid becoming white in air due to the formation of a film of sodium hydroxide and carbonate.

(ii) It dissolves in ice - cold water with hydrolysis, yielding hydrogen peroxide, which decomposes into water and oxygen on warming; whereas it gives oxygen and caustic soda with water at room temperature,

(iii)    It dissolves in ice-cold dilute mineral acid yielding H₂O₂.

Na₂O₂ + H₂SO₄ → Na₂SO₄ + H₂O₂ 

Potassium forms number of oxides namely,K₂O,K₂O₂ and KO₂ . Other two oxides can also exist which are K₂O₃ and KO₃ 

Potassium monoxide (K₂O)

It is solid, yellow when hot and white when cold, obtained by heating potassium nitrate with potassium.

2KNO₃ + 10K → 6K₂O + N₂

Potassium Superoxide (K₂O₂)

Controlled oxidation of potassium in excess air or oxygen at 300^o C gives mainly K₂O₂. It gives H₂O₂ when dissolves in water.

K₂O₂ + 2H₂O → 2KOH + H₂O₂

Potassium dioxide (KO₂)  

It is made by burning potassium in a good supply of air or oxygen. It is powerful oxidising agent. It reacts with water giving both oxygen and hydrogen peroxide.

2KO₂ + 2H₂O →2KOH + H₂O₂ + O₂

(i)     It is used as a bleaching agent.

(ii)    It is used in the manufacture of sodium perborate, benzoyl peroxide.

(iii)    It is used for the purification of air in confined spaces such as submarines.

Potassium metal is commercially prepared by the reduction of molten KCl with metallic sodium at 850^oC (1,123 K). This method is based upon the following principle:

(A)    Sodium is more reactive than potassium at this temperature

(B)    Potassium, being more volatile, distils off thus shifting the reaction forward

(C)    Sodium prefers to bind to chloride ions in preference to    potassium ions

(D)    Potassium and sodium form an alloy at this temperature