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- Oxygen and sulphur belong to group VI A. Oxygen shows a valency of -2, while sulphur shows a valency of -2, +4 and +6.
- Industrially oxygen is manufactured by fractional distillation of liquid air free of dust particles and CO2.
- Oxides of mercury, silver and lead decompose to give O2 on heating.
- Water on electrolysis liberates O2.
- Hydrogen peroxide decomposes at room temperature in the presence of catalyst MnO2 to liberate O2.
- Potassium and sodium nitrates decompose liberating O2.
- In the laboratory, O2 is prepared by heating a mixture of KClO3 and MnO2 (free charcoal).
- Oxygen is collected by downward displacement of water.
- Oxygen is non-combustible gas but a supporter of combustion. A glowing splint is rekindled in a jar of oxygen.
- Oxygen combines with most metals and non-metals to form the corresponding oxides.
- All hydrocarbons burn in oxygen to give carbon dioxide and water.
- Oxygen combines with colorless nitric oxide to form reddish brown fumes of nitrogen dioxide. This serves as a test for oxygen.
- Rusting is the oxidation of iron in the presence of oxygen and water vapor to give the hydrated oxide of iron.
- Rusting can be prevented by alloying; by electronic protection; by putting oil on the surface of the iron body; by electroplating i.e. applying a protective coating of metals like zinc, nickel or tin.
- Sulphur exhibits allotropy. The crystalline forms are rhombic and monoclinic sulphur and the amorphous forms are plastic, colloidal and milk of sulphur.
- There is a transition temperature of 96oC at which the two crystalline forms of sulphur coexist.
- Sulphur melts as 118.6oC and boils at 444oC.
- Sulphur combines with non-metals like oxygen, hydrogen, carbon and chlorine to form the corresponding sulphides.
- Sulphur combines with metals like Na and Hg at room temperature and metals like Fe, Cu, Zn at higher temperatures to form sulphides.
- Sulphur is oxidized to sulphur dioxide by oxidizing acids like concentrated H2SO4 and concentrated HNO3.
- Sulphur mixed with charcoal and potassium chlorate is called gun powder and forms an explosive mixture.
- Rubber when heated with sulphur gives vulcanized, hard rubber, which is used to make automobile tyres.
- Sulphur has medicinal properties and even acts as a fungicide and insecticide.
