A small amount of the compound is dissolved in 1 mL of water. Two drops of 1 M copper(II) sulfate are added. If a blue color is not formed immediately, then heat the test tube in a hot water bath for 5 min.
A moderate to deep blue color of a liquid or a dark blue solid is a positive test.
Some a-amino acids are not very soluble in cold water. However, these amino acids are soluble in hot water and will give a positive test when the solution is heated. Aliphatic amines yield a blue precipitate. Anilines give a brown or green color, but other aromatic amines produce a blue-purple color.
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