![]() ![]() It is also used in certain electric batteries. Mercury is used as an electrode in the production of chlorine and sodium hydroxide. It is used in mercury-vapor lamps, which emit light rich in ultraviolet radiation various kinds of such lamps are used for street lighting, as sun lamps, and in “black lights” (see lighting). Mercury is important as a liquid contact material for electric switches. ![]() Because it has a high rate of thermal expansion that is fairly constant over a wide temperature range, it is used extensively in thermometers. Because of its high density, it is used in barometers and manometers. The metal is usually purified by repeated vacuum distillation. The metal is obtained commercially from cinnabar, a mercuric sulfide ore it is easily separated by roasting the ore in air. Mercury occurs uncombined in nature to a limited extent. A mercurous oxide may be formed chemically but is unstable, decomposing to a mixture of mercury and mercuric oxide. At elevated temperatures mercury reacts slowly with oxygen to form mercuric oxide, HgO. Mercury reacts directly with the halogens to form mercuric salts. Mercury reacts with hot concentrated sulfuric acid to form mercuric sulfate, HgSO 4 with excess mercury, mercurous sulfate, Hg 2SO 4, is formed. An excess of mercury reacts with nitric acid to form mercurous nitrate, HgNO 3. It reacts with hot nitric acid to form mercuric nitrate, Hg(No 3) 2. Mercury is not attacked by dilute hydrochloric or sulfuric acid. Mercury forms numerous compounds, assuming +1 valence in mercurous compounds and +2 valence in mercuric compounds.
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