A Course in Qualitative Chemical Analysis

f the metals of this group are insoluble in water. Silver 1. Hydrochloric acid or a soluble chloride, when added to solutions of silver salts, gives a white, curdy precipitate of silver chloride (AgCl) which darkens on exposure to light. The precipitate is insoluble in water, the solubility being approximately 1 part in 700,000 parts of water ; it is insoluble in dilute acids and in dilute aqua regia, but is somewhat soluble in concentrated acids. Ammonium hydroxide readily dissolves it, with the formation of silver ammonia chloride AgCl + 2 NH, = Ag(NHCl, from which AgCl reprecipitates orhacidincation with nitric acid : ? Ag(NH3)2Cl + 2 HNO3 = |gCl + 2 NH4NO3. Silver chloride also dissolves in somtions of potassium cyanide and sodium thiosulphate; when cautiously heated, it fuses without decomposition. 2. Hydrogen Sulphide and soluble sulphides precipitate black Ag2S, insoluble in cold dilute acids, alkali hydroxides, and alkali sulphides ; it is soluble in hot dilute HNO3, with the formation of AgNO3 and separation of sulphur. The reaction can be considered as taking place in two steps, the first consisting of the solution of the sulphide with the liberation of H2S and the second of the oxidation of the H2S by the excess of HNO3 present with the formation of water, nitric oxide, and the separation of sulphur: ? (1) Ag2S + 2 HN03 = 2 AgN03+fH2S; (2) 2HN03 + 3 H2S = 4H20 + f2NO + |3S. Multiplying equation (1) by 3 and adding it...