After a positive test, the bromine water becomes what color?

• A. Colorless
• B. Orange-brown
• C. Blue
• D. Green

Answer: (A)

Bromine water is orange-brown because it contains Br2. A positive test for unsaturation happens when a compound with a carbon–carbon double bond reacts with Br2, adding across the double bond to form a dibromo compound. This reaction uses up the Br2, so the colored bromine is removed and the solution turns colorless. If there’s no double bond, as with alkanes, the bromine water stays orange-brown.