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分析化学中的沉淀方法,经过逐渐的发展,已形成了有明显区别的三种沉淀方法,卽(1)常法沉淀(非均匀沉淀),(2)均匀沉淀,(3)小体积沉淀。均匀沉淀与小体积沉淀是为了减少沉淀对其他元素的共沉淀所采取的二种不同沉淀方法。在化学意义上,这二种方法各趋极端。在均匀沉淀的整个过程中,沉淀剂的浓度保持在必需的最低水平,使沉淀缓缓生成。相反,小体积沉淀则须在沉淀之前将溶液蒸发至2—3毫升,加入大量固体盐(例如5克氯化銨),搅拌均匀,此时溶液已分布在固体盐表面而呈干涸状态,然后加入大量浓沉淀剂(例如10毫升浓氨水),使沉淀迅速生成,最后加足量水以溶解固体盐使与沉淀分离,至此沉淀过程已完毕,卽可过滤。
Analytical chemistry precipitation method, through the gradual development, has formed a clear distinction between the three precipitation methods, 卽 (1) often precipitation (heterogeneous precipitation), (2) uniform precipitation, (3) small volume precipitation. Homogeneous precipitation and small volume precipitation are two different precipitation methods taken to reduce coprecipitation of other elements by the precipitation. In the chemical sense, these two approaches tend to be extreme. In the course of uniform precipitation, the concentration of precipitant is kept at the minimum necessary to allow the precipitate to form slowly. Conversely, small volumes of sediment must be evaporated to 2-3 ml prior to precipitation. A large amount of solid salt (eg, 5 g ammonium chloride) is added and the mixture is stirred until the solution has spread to the surface of the solid salt and dried. Add a large amount of concentrated sediment (for example, 10 ml of concentrated ammonia), so that the precipitate quickly formed, and finally add enough water to dissolve the solid salt to separate the precipitate, thus the precipitation process has been completed, 卽 can be filtered.