Cyclohexene + Bromine Water? (1 Viewer)

[benlagoon]

Hey this has left me confused for a while now. What is the reaction for cyclohexene + bromine water?

I have seen some sources where it is shown as: C6H10 + Br2 --> C6H10Br2
This however does not show bromine water rather, bromine itself

Other sources have shown it as: C6H10 + BrOH --> C6H10BrOH

Which one is the HSC approved one?

Thanks!

 

[Kimyia]

I would personally use the second one because I think its more correct in actually showing bromine water but I was worried about that too because my textbook has both (I think it was my textbook....)

 

[RANK 1]

Hey this has left me confused for a while now. What is the reaction for cyclohexene + bromine water?

I have seen some sources where it is shown as: C6H10 + Br2 --> C6H10Br2
This however does not show bromine water rather, bromine itself

Other sources have shown it as: C6H10 + BrOH --> C6H10BrOH

Which one is the HSC approved one?

Thanks!

u can use both it doesnt matter just make sure u know how to draw it

 

[rolpsy]

both are accepted by the board of studies.

I prefer this one because it's simpler
C₆H₁₀(l) + Br₂(aq) –> C₆H₁₀Br₂(l)

edit: take a look at this for more info

 

[Kimyia]

both are accepted by the board of studies.

I prefer this one because it's simpler
C₆H₁₀(l) + Br₂(aq) –> C₆H₁₀Br₂(l)

edit: take a look at this for more info

^ Thanks for the link. That most definitely cleared things up.

 

[Sanical]

So it's fine to write BrOH or Br₂?
If so, if you use BrOH, if added in cyclohexane, wouldn't the colour become lighter as the non-polar cyclohexane is soluble in the non-polar part of bromine water, leaving an aqueous clear layer?

 

[asdfqwerty]

BrOH is technically the correct term (our teacher actually sent an email asking the university of sydney in the chem department and they validated it as correct). But it's fine to write both.

people prefer to use Br2 because if you use BrOh, the resulting chemical formula for the addition reaction of cyclohexene will be a bitch to draw (remember, they will most likely ask you to draw a STRUCTURAL formulae and also name the substance).

If you add bromine water with cyclohexane, there will be no colour change. It does not matter if it leaves an aqueous clear layer or not and they will never ask you to account for its polarity in bromine water. remember, the experiment is to distinguish an alkene with its corresponding alkane so the only observation that you should be worry about is the decolourisation of bromine water, and to account for that, its because of the double bond of cyclohexene making it more reactive than cyclohexane.

they will most likely not ask you to draw a structural formula for cyclohexane reacting with bromine water, because substitution reaction is not in the syllabus.

hope it helps and clarify a few bit.

 

[Sanical]

so would you say for alkanes that there was no colour change or no reaction? Or both?

 

[Kimyia]

so would you say for alkanes that there was no colour change or no reaction? Or both?

there is still a reaction with alkanes...its just damn slow. the substitution reaction would take a while and works best under UV light. the bromine water test relies on observing which causes rapid decolourisation. so its just no observable colour change.

 

[asdfqwerty]

For cyclohexane, say that bromine water did not colourise in the abscence of UV light and remained yellow before and after shaking. Therefore, no reaction has occurred. therefore, it shows that cyclohexene is more reactive than cyclohexane.

you must mention the sentence in bold because thats what the experiment is about. to say that bromine water didnt decolourise in cyclohexane is not good enough and does not answer the aim (because you are doing it in the first place to compare its reactivity with another substance ie. cyclohexene).

 

[Sanical]

Ok thanks guys.

 

[Sanical]

And just saying, I think it's more correct to write HOBr (as opposed to BrOH)

 

[Sanical]

Wait lol,
Should you mention in the method to cover the alkane test tubes in aluminium foil?
Also, should there be a control?

So many questions!!

 

[asdfqwerty]

Not necessarily. You don't have to. But the control would be equal volume of cyclohexane/hexene and amounts of bromine water used in each test tube, and also the same type of test tube.

 

[Sanical]

Not the controlled variables, but the control as in something you compare to.

 

[Kimyia]

Not the controlled variables, but the control as in something you compare to.

You can get just an empty test tube, add bromine water to it and observe the colour. Then use that as a comparison for colour and prove that no other variables are causing the colour change.

 

[xnerd96x]

oohhh... this was my favourite experiment to explain:

Ok Alkanes only undergo substitution reactions, in UV light we see that they react with the bromine solution because the Uv produced free radicals which could then react

Alkene is reactive because of the electron density at the double bond area, so it will undergo addition reactions with the bromine water, thus removing the Br2 ions from the reaction equilibrium, and therefore causing a colour change.

we always have this arguement with out chem teacher about which formular of bromine water to use - but really, as it is only the bromine ions which react here, if you used the simplified equation its all good!!!!!!

 

[someth1ng]

Just to clarify, is the bromine water in the test tube and you add drops of the alkane/alkene or is the alkane/alkene in the test tube and you add drops of bromine water?

Or does it not matter?

 

[madharris]

Just to clarify, is the bromine water in the test tube and you add drops of the alkane/alkene or is the alkane/alkene in the test tube and you add drops of bromine water?

Or does it not matter?

It doesn't matter


However, i've read in multiple sources that you need to put more of one than the other but they all say different things
(like more or bromine than hydrocarbon or more hydrocarbon than bromine water)

does anyone know

 

[someth1ng]

It doesn't matter


However, i've read in multiple sources that you need to put more of one than the other but they all say different things
(like more or bromine than hydrocarbon or more hydrocarbon than bromine water)

does anyone know

In that case, the amount ratio doesn't matter. You just need to say that the hydrocarbon decolourises the bromine water and it should be all good - assuming it doesn't matter which is in the test tube etc.