Treating an aldehyde with Fehling’s reagent produces a precipitate of what color_________________?
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Answer: D. brick red
Explanation
Fehling's reagent contains alkaline copper(II) tartrate complex ions that oxidize aldehydes to carboxylate ions. During this redox process, the copper(II) ions are reduced to insoluble copper(I) oxide precipitate. Copper(I) oxide naturally exhibits a distinct and characteristic brick-red color upon precipitation. Chemical tests for functional groups help identify unknown organic compounds in analytical laboratories. Aliphatic and aromatic aldehydes react differently, with aliphatic aldehydes giving positive Fehling tests. Heating the mixture is necessary to drive the precipitation reaction of the copper oxide.
Clinical laboratories historically utilized similar reduction tests to detect glucose in biological fluid samples. Qualitative organic analysis relies on color changes to verify the presence of specific functional groups. Distinguishing reducing sugars from non-reducing carbohydrates often involves copper-based reduction reagents. Option A is incorrect because copper(I) oxide does not produce any pink coloration. Option B is incorrect as elemental copper precipitates do not appear black in this test. Option C is incorrect because yellow precipitates are not characteristic of this copper reduction.
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