Describe how you test for an aldehyde or ketone and distinguish between the two.
To test for an aldehyde or ketone you would use 2,4-dinitrophenylhydrazine (2,4-DNP). 2,4-DNP mixed with methanol and sulphuric acid is knows as Brady's reagent. If a yellow/orange precipitate is formed when Brady's reagent is added to a mystery solution it indicates the presence of a C=O bond found in aldehydes and ketones. To further distinguish between the two, you would add aqueous sodium hydroxide and aqueous silver nitrate to the original sample until a brown precipitate forms. Then add dilute aquoeus ammnia until the precipitate just dissolves. This combinbation of reagents is known as Tollen's Reagent. If a silver grey solid or mirror like effect is formed, an aldehyde is present. If a ketone is present, there will be no reaction.
SJ
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