Question (1 Viewer)

[schooly]

Hi, just wanted to ask a question that always got me thinking and never understood it.
Q: How would you distinguish between for example Hexane and Hexene?
i understand that one is single bond and one is double bond but say u got two beakers with each one in it and no labels, how would u tell which is hexane and which is hexene?
thankyou

 

[ND]

Originally posted by schooly
Hi, just wanted to ask a question that always got me thinking and never understood it.
Q: How would you distinguish between for example Hexane and Hexene?
i understand that one is single bond and one is double bond but say u got two beakers with each one in it and no labels, how would u tell which is hexane and which is hexene?
thankyou

I think you could add bromine water to both solutions, in the hexene the bromine water would react with it, in the hexane it wouldn't.

 

[Ultimate]

Re: Re: Question

Originally posted by ND


I think you could add bromine water to both solutions, in the hexene the bromine water would react with it, in the hexane it wouldn't.

yeah thats correct. The bromine water breaks the double bond of hexene, thereby decolourising the bromine water.

 

[-=«MÄLÅÇhïtÊ»=-]

juz make sure u dun imply that the decolourisation is due to the breaking of the double bond (coz i had picky science teachers who loved taking marks off). its coz the bromine attaches to the hexene using the double bond, thus reducing the brown colour in the solution.

the answer to this can be found in how to distinguish alkanes and alkenes. You'll usually be asked hexane/hexene coz its a liquid during room temp.

 

[Ultimate]

Originally posted by -=MLhtʻ=-
juz make sure u dun imply that the decolourisation is due to the breaking of the double bond. its coz the bromine attaches to the hexene using the double bond, thus reducing the brown colour in the solution.

thats why you would draw a structural diagram to show what you are talking about

 

[wogboy]

Also remember that you need to do this test WITHOUT the presence of UV light, because if there's UV light the hexane will react with the Bromine as well as the hexene.

 

[kini mini]

Originally posted by wogboy
Also remember that you need to do this test WITHOUT the presence of UV light, because if there's UV light the hexane will react with the Bromine as well as the hexene.

And in that case, the reaction is much slower so you'll see the solution decolourise, but slowly.

 

[timmii]

Just to clarify:

The addition of bromine water to hexane is a substitution reaction and occurs only really in the presence of UV light. I.e in ur structural formulae, Br2 becomes HBr as one of the Br's take the place of a H in the hexane molecule.

The addition of bromine water to hexene is called an addition reaction, and it will occur relatively quickly in normal light conditions. The double bond opens to include the two bromine atoms, thereby decolourising the solution.