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Chemical formula: Na2O2. It belongs to peroxides and is an ionic compound. It contains Na+ and O22- (or O—O2-) peroxide ions; in O—O2-, there are covalent bonds between the oxygen atoms. It is a pale yellow powder; commercial sodium peroxide is usually made into small round particles. It has strong oxidizing properties and can strongly oxidize certain metals; for example, it can oxidize iron to form ferrate FeO2-4. Even at room temperature, it is capable of oxidizing all organic substances into carbonates. It can easily catch fire when placed together with ethanol and other flammable materials. It hardly decomposes in its molten state, but can explode when in contact with cotton, carbon powder, or aluminum powder; care must be taken when using it. It is hygroscopic, and when it reacts with water or dilute acids, hydrogen peroxide (H2O2) is produced, resulting in intense heat release. The H2O2 produced is unstable and releases oxygen immediately; therefore, boiling an aqueous solution of Na2O2 also releases oxygen. Na2O2 exhibits reducibility when reacting with strong oxidizing agents such as KMnO4. Insoluble in ethanol. It can react with carbon dioxide in the air to release oxygen, and is therefore commonly used in environments where there is a lack of air, such as mines, tunnels, during diving, and on spacecraft. It can convert the CO2 exhaled by people back into O2 for human respiration. It is commonly used in industry as a bleaching agent, bactericide, disinfectant, deodorizer, oxidizing agent, etc. It can usually be prepared by heating metallic sodium in dry air free of CO2 to 300°C. Due to its hygroscopic nature and tendency to react with CO2, it must be stored in a sealed container.