The formation of precipitation, which is produced by mixing a metal ion solution with a solution of reagent, is hard to observe in a test tube, as precipitation immediately occurs and forms a lump. In classroom experiments focusing on precipitation at senior high school, a problem has been the overuse of reagent. As some gaseous materials evaporating from its solution are harmful to health, the smallest possible amount of reagent has to be used. The author had already reported that salt crystals produced by the reaction of acid gas with alkaline solution can be observed through the microscope. In this study, the author will report that the formation and process of precipitation can be observed easily with a CCD camera attached to a microscope. This article deals with the practice at university and its application at senior high school using the proposed method. The reaction of limewater with carbon dioxide was carried out at university, and the students were interested in observing the formation and dissolution of calcium carbonate precipitation. As an application of the proposed method, the reaction of metal ions with ammonia and hydrogen chloride will be practiced at senior high school. The formation and dissolution of each precipitation will be observed with greater interest.
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