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Explain about 3 test for aldehyde |
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Answer» Solution : (i) Tollen.s reagent test: When an ALDEHYDE is warmed with Tollens reagent (AMMONICAL silver nitrate), a bright silver mirror is produced due to the formation of silver metal. This reaction is also CALLED silver mirror test for aldehydes. `CH_3CHO + 2 [Ag (NH_3)_2]^(+) + 3OH to CH_3COO^(-) + 4NH_3 uarr + underset("silver mirror ")(2Ag uarr + 2H_2O) ` (ii)Fehlings solution Test: Fehlings solution is prepared by mixing equal volumes of Fehlings solution ‘A’containing aqueous copper sulphate and Fehlings solution .B. containing alkaline solution of sodium potassium tartarate (Rochelle salt) When aldehyde is warmed with Fehlings solution DEEP blue colour solution is changed to red precipitate of cuprous oxide. `underset("blue")(CH_3CHO+2Cu^(2+) + 5OH) to underset("red")(CH_3COO + Cu_2O darr+ 3H_2O)` (iii) Benedict.s solution Test: Benedict.s solution is a mixture of `CuSO_4`+ sodium citrate + `NaOH. Cu^(2+)`is reduced by aldehyde to give red precipitate of cuprous oxide. `underset("blue")(CH_3CHO + 2Cu^(2+) + 5OH) to underset("red")(CH_3COO + Cu_2O + 3H_2O)` |
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