Place 2 mL of Schiff's reagent in a test tube and add 2 drops or a few crystals of the unknown. Shake the tube gently, and observe the color that is developed in 3-4 min. Aldehydes react with Schiff's reagent to form a complex which has a wine-purple color.
Schiff's Reagent: Dissolve 0.05 g of pure fuchsin (4-rosaline hydrochloride) in 50 mL of distilled water. Add 2 mL of saturated sodium bisulfite solution. After allowing the solution to sit for 1 hr, add 1 mL of concentrated hydrochloric acid. Allow to stand overnight. This reagent is practically colorless and very sensitive.
Formation of a violet-purple solution is a positive test.
In this test the reagent should not be heated, and the solution tested should not be alkaline. When the test is used on an unknown, a simultaneous test on a known aldehyde and a known ketone should be performed for comparison.
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