Sodium peroxide, Na₂O₂

The Sodium peroxide, Na₂O₂, is manufactured by the action of dry air, free from carbon dioxide, on sodium in an iron tube at 300° C., the only process employed for its production on the large scale. The commercial article contains about 93 per cent, of sodium peroxide.

Sodium peroxide has a yellowish colour. It is not decomposed by heat, but is a very powerful chemical reagent, in many respects resembling hydrogen peroxide.

It can act as a reducer, decomposing salts of silver, gold, and mercury, with evolution of oxygen. As an oxidizer, it reacts energetically with silver, tin, and lead. It converts the oxides of carbon into sodium carbonate, and nitrogen monoxide and nitric oxide into sodium nitrate. It is reduced to sodium by charcoal or carbides of the alkaline-earth-metals. It reacts with ammonia, forming sodium hydroxide and evolving nitrogen:

2NH₃+3Na₂O₂ =N₂+6NaOH.

It oxidizes organic substances very energetically, and finds application in organic analysis.

The peroxide is not deliquescent, but dissolves in water with evolution of oxygen, hydrogen peroxide being a primary product:

Na₂O₂+2H₂O =H₂O₂+2NaOH.

The reaction is reversible, since sodium peroxide is formed by the interaction of hydrogen peroxide and sodium hydroxide. When a mixture of aqueous hydrogen peroxide and sodium hydroxide as solid or in solution is cooled, a quantitative yield of a crystalline hydrate, Na₂O₂,8H₂O, with mother-of-pearl lustre is obtained. This hydrate is also produced by exposing the peroxide to air in absence of carbon dioxide, and forms white crystals soluble in water without evolution of oxygen, this property facilitating the production of a concentrated solution of hydrogen peroxide. Decomposition of the solution begins at 30° to 40° C., and is complete at 100° C., oxygen being evolved. A dihydrate is precipitated by addition of alcohol to a mixture of hydrogen peroxide and sodium hydroxide, or by keeping the octahydrate over concentrated sulphuric acid. A tetrahydrate is also mentioned by Schone.

For the heat of formation of sodium peroxide from its elements, de Forcrand gives 119.8 Cal. And 119.73 Cal.

Sodium peroxide is employed in the laboratory and in the arts as an oxidizer. With acids it forms addition-products of the type Na₂O₂,2HCl, obtained by the action of dry hydrogen chloride on a suspension of the peroxide in carbon tetrachloride. The compound formulated is a white powder, and on treatment with water yields a solution containing 10 per cent, of active oxygen.

Carbon monoxide converts sodium peroxide into sodium carbonate. The action of carbon dioxide is similar, but much more energetic, oxygen being evolved.

For the estimation of sodium peroxide, Niemeyer recommends titration with standard potassium permanganate in presence of sulphuric acid:

2KMnO₄+5Na₂O₂+8H₂SO₄=K₂SO₄+5Na₂SO₄+2MnSO₄+8H₂O+5O₂.

de Forcrand mentions two other sodium peroxides, Na₂O₃ and Na₂O₄. The heat of formation of the first from the elements is given as approximately 126.7 Cal., and of the second as approximately 130 Cal.