Solution is "decolorized" (Quiz 3 Prep)

[Kira_Maszewski_1B]

When ethene is bubbled through bromine water, the solution is decolorized. Which of the following is true regarding the reaction?

1. Br2 acts as a nucleophile
2. Br2 attacks the carbons of the double bond in one step.
3. The first step is the removal of a hydrogen atom to form [C2H3]-
4. The Br- ion attacks the same face of the bromonium ion.
5. The Br2 acts as a nucleophile.

Please help! I am very confused on what to do here. By the way this is question 8 on the Quiz 3 practice test.

[breinhardt3G]

So the answer is actually the last option (you misread, the last option in the course reader actually reads "Br2 acts as an electrophile.") The reason being is that the ethene molecule is electron rich with its double bond so in the halogenation reaction, the electrons from the double bond in the ethene react to form 1,2-dibromoethane. Thus the bromine is the electrophile in this situation and the solution is decolorized because the bromine solution (which is normally a brownish color) reacts to form a new compound with ethene.