Why does bromine change color

The other halogens, apart from fluorine, behave similarly. Fluorine reacts explosively with all hydrocarbons - including alkenes - to give carbon and hydrogen fluoride. If you are interested in the reaction with, say, chlorine, all you have to do is to replace Br by Cl.

The reaction is an example of electrophilic addition. The bromine is a very "polarizable" molecule and the approaching pi bond in the ethene induces a dipole in the bromine molecule. If you draw this mechanism in an exam, write the words "induced dipole" next to the bromine molecule - to show that you understand what's going on. In the first stage of the reaction, one of the bromine atoms becomes attached to both carbon atoms, with the positive charge being found on the bromine atom.

A bromonium ion is formed. Figure: Step 1 in mechanism of addition of Bromine to ethene. The bromonium ion is then attacked from the back by a bromide ion formed in a nearby reaction.

Why is there a color change when ethene reacts with bromine? Nov 2, Because neither ethylene nor ethyl bromide have a characteristic colour.

Explanation: On the other hand, bromine has a characterstic red-orange colour. Related questions Question fee Question c5c Question 19eb9. UV light is the condition under which the reaction will occur so it is written above the arrow in the chemical equation. During this reaction, bromine atoms substitute for replace hydrogen atoms, one at a time, initially producing bromoethane ethyl bromide and hydrogen bromide as shown in the chemical equation below:. The halogenation of ethane is not usually demonstrated in the school laboratory because ethane is a gas at room temperature and pressure.

Cyclohexane, however, is a liquid alkane at room temperature and pressure, and this is the alkane most often used to demonstrate: a lack of reaction with bromine water under standard laboratory conditions b slow reaction with bromine water under UV light.

Play the game now! In an alkene containing only one double bond, the double bond is broken, the halogen atoms are added, and, the only product of the reaction will be a dihaloalkane. In a bromination reaction for example, if excess alkene is present, then the reaction mixture will change from a red-brown colour to colourless. Ethene will readily react with bromine, so the colour of the bromine water changes from red-brown to colourless.

Bromine atoms will add across the double bond in ethene to produce just one product; 1,2-dibromoethane. The addition of bromine across the double bond in ethene is not usually demonstrated in school laboratories because ethene is a gas at room temperature and pressure.