To a solution or suspension of 0.2 g of unknown in 5 mL of water, add 5 mL of Benedict's solution. If no precipitate is formed, heat the mixture to boiling and cool.
Benedict's solution: A solution of 17.3 g of sodium citrate and 10.0 g of anhydrous sodium carbonate in 80.0 mL of water is heated until the salts are dissolved. Additional water is added to bring the volume up to 85.0 mL. A solution of 1.73 g of hydrated copper sulfate in 10.0 mL of water is poured slowly with stirring into the solution of the citrate and the carbonate. Add water to make a final volume of 100 mL.
Precipitation of copper(I) oxide as a red, yellow, or yellowish-green solid is a positive test.
Not general for simple aldehydes and ketones.
Hydrazine derivatives give a positive test.
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