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铁丝在氧气里的燃烧:(初中课本演示实验1—3,P_(12))这里的关键是选择含碳量较低的铁丝.钢丝含碳较高,且含合金元素,不适用.可把窗纱上拆下的铁丝打光使用.铁丝绕成螺旋形也很重要,螺距不可太宽,以免热量不集中,不易引燃.火柴梗只要一根火柴的三分之一,把它充分燃过再伸入瓶中,以兔火柴梗消耗过多的氧气.碘离子的检验:(初中课本实验八,P_(224))把AgNO_3溶液滴入KI溶液,产生黄色AgI沉淀,滴几滴稀硝酸,沉淀不溶解.但有时会出现溶液变为橙黄色的现象.这是因为所用的硝酸不够稀,把剩余的I~-氧化成I_2,少量的I_2溶解在水中呈橙黄色.这个实验关键在于硝酸的浓度,一般用1:5的稀硝酸或者更稀一点,即可避兔干扰.也可采用两种改变程序的方法来消除这种干扰.一是在产生沉淀后分离沉淀,然后对沉淀滴入稀硝酸;二是先给试管注入AgNO_3溶液,然后往试管内滴加KI,产生沉淀后加稀硝酸.
The burning of iron wire in oxygen: (The junior high school textbook demonstration experiment 1-3, P_(12)) The key here is to choose the carbon wire with lower carbon content. The steel wire contains higher carbon and contains alloying elements. It is not applicable. The iron wire removed from the screens is used for lightening. It is also important that the wire is wound into a spiral shape. The pitch should not be too wide so that the heat is not concentrated and it is not easy to ignite. The matchstick needs only one third of a match to burn it completely. Then extend into the bottle to consume too much oxygen in the rabbit matchstick. Iodine ion test: (Junior Textbook Experiment 8, P_(224)) Drop the AgNO 3 solution into the KI solution to produce a yellow AgI precipitate with a few drops of dilute nitric acid The precipitate does not dissolve, but sometimes the solution turns orange yellow. This is because the nitric acid used is not dilute enough to oxidize the remaining I~- to I_2, and a small amount of I_2 is dissolved in water to appear orange-yellow. The key to this experiment lies in The concentration of nitric acid, usually 1:5 dilute nitric acid or a bit more dilute, can avoid rabbit interference. Two methods of changing the program can also be used to eliminate this interference. One is to separate the precipitate after precipitation and then to precipitate. Dilute nitric acid; secondly, inject AgNO_3 solution into the test tube first, then add KI to the test tube. Add dilute nitric acid after precipitation.