Aldehydes and ketones
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I'd like to know why is ammonia solution used in the Tollen's reagent?
250509
Corrie writes ...
Tollen's reagent works by the aldehyde behaving as a reducing agent, reducing silver ions to metallic silver.
If aqueous silver nitrate is used, the silver is produced as a finely-divided black solid. However, if the Ag+(aq) ions are first converted to the ammonia complex ion, [Ag(NH3)2]+, by the addition of ammonia, then reduction takes place more slowly, allowing the silver to form as a mirror on the glass surface of the container used.
Sometimes, even when using Tollen's reagent carefully, a fine, black precipitate of silver is produced instead of a mirror despite the glass container having been thoroughly cleaned.
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updated: 26 May 2009
