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Mercury forms halides in the two oxidation states, +1 and +2. 1. Mercury(1)Chloride(Hg2Cl2) Mercury(1) chloride or mercurous chloride is known as calomel. Preparation Mercury(1)chloride is prepared by heating a mixture of mecury(2)chloride and mercury in iron vessel. HgCl2 + Hg -------> Hg2Cl2 It can also be obtained by reduction of mercury(2)chloride by reducing agents like tin(2)chloride in limited quantity. 2HgCl2 + SnCl2 --------> HgCl2 + SnCl4 Properties When heated, mercury(1)chloride decomposes into mercury(2)chloride and mercury. Hg2Cl2 -------> HgCl2 + Hg The action of aqueous ammonia on the solid mercury(1)chloride gives a mixture of black finely divided mercury and white mercury amino chloride. This reaction is an example of disproportion reaction. Hg2Cl2 + 2Nh3 -------> Hg(NH2)Cl + Hg + NH4Cl Uses of mercury(1)chloride Calomel is used in making standard calomel electrodes used as secondary reference electrode. It is also used as a purgative in medicines. 2. Merc...

Preparation Silver nitrate is prepared by dissolving silver in dilute nitric acid. 3Ag + 4HNO3 ------> 3AgNO3 + 2H2O + NO Properties Silver nitrate on heating decomposes to form silver, nitrogen dioxide and oxygen. 2AgNO3 ---------> 2AgNO2 + O2 AgNO2 ---------> Ag + NO2 Silver nitrate is also decomposed by organic matter, such as glucose, paper, skin and cork. It has also a caustic and destructive effect on organic tissues. Uses of silver nitrate Large quantities of silver nitrate are used in the production of light sensitive plates, film and papers. In the laboratory it is used as a reagent for the detection of halide ions. It is used in making inks and hair dyes. In small doses, silver nitrate is used as a medicine for nervous diseases. Silver halides Silver fluorides may be prepared by the action of hydrofluoric acid on silver(1) oxide. Ag2O + 2HF -------> 2AgF + H2O Silver chloride, silver bromide and silver iodide are prepared by the action of silver nitrate on sodium ...