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Tollens' reagent is a chemical reagent used to determine the presence of an aldehyde or alpha-hydroxy ketone functional groups. The reagent consists of a solution of silver nitrate and ammonia. It was named after its discoverer, the German chemist Bernhard Tollens. A positive test with Tollens' reagent is indicated by the precipitation of elemental silver, often producing a characteristic "silver mirror" on the inner surface of the reaction vessel. ==Laboratory preparation== This reagent is not commercially available due to its short shelf life. It must be freshly prepared in the laboratory. One common preparation involves two steps. First a few drops of dilute sodium hydroxide are added to some aqueous silver nitrate. The OH− ions convert the silver aquo complex form into silver oxide, Ag2O, which precipitate from the solution as a brown solid: :2 AgNO3 + 2 NaOH → Ag2O (s) + 2 NaNO3 + H2O In the next step, sufficient aqueous ammonia is added to dissolve the brown silver(I) oxide. The resulting solution contains the ()+ complexes in the mixture, which is the main component of Tollens' reagent. Sodium hydroxide is reformed: :Ag2O (s) + 4 NH3 + 2 NaNO3 + H2O → 2 ()NO3 + 2 NaOH Alternatively, aqueous ammonia can be added directly to silver nitrate solution.〔 At first, ammonia will induce formation of solid silver oxide, but with additional ammonia, this solid precipitate dissolves to give a clear solution of diamminesilver(I) complex ( ()+). Filtering the reagent before use helps to prevent false-positive results. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tollens' reagent」の詳細全文を読む スポンサード リンク
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