Need help to write out experiment with chyclohexene and cylcohexane and bromine water (1 Viewer)

[-s2-]

ahhhh dunno how to write experiment...

 

[pLuvia]

Have you done the experiment?

Using the search function here is a prac written up before
http://community.boredofstudies.org/2205778/post-4.html

 

[Forbidden.]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

That's in the HSC Course and you worry about it now ?

LOL I'll pretend yuo are an examiner, here goes:


Before commencing the experiment, safety measures such as wearing a lab coat may be required to minimise risks.

Pour cyclohexane in one test tube and cyclohexene in the other test tube, label them or remember its contents.

Pour bromine water in cyclohexene and stir it around. The brown colour of bromine water should fade and become colourless with cyclohexene. This reaction is called the addition reaction, the double bonds in cyclohexene break to form single bonds to accomodate two bromine atoms, the compound now becomes dibromohexane.

Pour bromine water in the other test tube with cyclohexane and stir it around. The colour of brown bromine water should still partially remain. If any react, the reaction is called the substitution. Two hydrogen atoms will immediately be removed from the bonds and are replaced by two bromine atoms, which may become dibromohexane, cyclohexane may still remain in the test tube.

That's 3-6 marks for me ! Depending on how much it's worth.

 

[Forbidden.]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

According to the link pLuvia posted, we never used foil or a UV lamp or any kind of UV light-emitting apparatus for our experiment. I forgot to mention dibromocyclohexane and I have not fully explained about the decolourisation of the colour of bromine water or even give the proper molecular formulas e.g H₂OBr₂ or C₆H₁₂

 

[airie]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

And btw, just a general rule of thumb: wash all components of your apparatus (scratch stuff like Bunsen burner, I meant things like test tubes, flasks etc ) before the experiment. I lost half a mark for not including the step in the what-to-do flowchart for this prac in the prelim yearly

 

[Pugsley]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

When you mix hexane with the bromine how come there arent two distinct layers? It just turns in to a brown/red murky solution.

Also, where should the safety precautions and all that be written?

Can someone please explain how the hexane/bromine would or should look like in a test tube once mixed?

Is the hexene/bromine(1,2 dibromohexane) solution meant to be completely clear?

Should i just assume we are using 1-hexene when writing out the practical and doing the equations?

Can someone explain the chemistry of why the hexene actually decolorises the bromine?
I understand they react due to the double bond and halogenation occurs but does it have something to do with it being a diatomic molecule before the reaction are just the simple fact that there is alot less bromine present in each molecule?

Assistance would be greatly appreciated, thanks in advance.

 

[phil2010]

Have you done the experiment?

The actual experiment can be viewed at ...
http://www.chem.uiuc.edu/clcwebsite/cyclo.html

 

[Forbidden.]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

And btw, just a general rule of thumb: wash all components of your apparatus (scratch stuff like Bunsen burner, I meant things like test tubes, flasks etc ) before the experiment. I lost half a mark for not including the step in the what-to-do flowchart for this prac in the prelim yearly

Thanks, except in the HSC there is no half-mark, either no mark or one whole mark. But now you know your mistake, I know your mistake, it hopefully won't happen again.

 

[jest3r]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

Can someone explain the chemistry of why the hexene actually decolorises the bromine?
I understand they react due to the double bond and halogenation occurs but does it have something to do with it being a diatomic molecule before the reaction are just the simple fact that there is alot less bromine present in each molecule?

Assistance would be greatly appreciated, thanks in advance.

As far as I know, the colour change is only in relation to whether the solution is an alkane or an alkene. Correct me if I am wrong.

 

[yoakim]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

Hopefully this explanation will help those who are having trouble.


Safety precautions:
· Use a fume cupboard for storing open containers
· Wear a lab coat to prevent absorption through the skin
· Wear glasses to prevent entry through the eyes
· Do not breath in directly or waft smell

Method:
1. Set up 2 test tubes.
2. Add i) cyclohexene and ii) cyclohexane in the test tubes (separately).
3. Add a small amount of bromine water (recommended 8 drops). Add a stopper onto the test tubes.
4. Leave it exposed to sunlight/UV.
5. Repeat experiment, but wrap aluminium foil around the test tube instead of exposing it to sunlight.
6. Place stoppers on all test-tubes.
7. Record observations.


Observations:

Before Mixing:

Bromine Water:
- Clear
- Orange
- Liquid
- Strong Smell

Cyclohexane:
- Clear
- Colourless
- Liquid

Cyclohexene:
- Clear
- Colourless
- Liquid


After Mixing:

Cyclohexane and Bromine Water:
- Two distinct separate layers after instantaneous reaction
- Cyclohexane lies on top of the Bromine water

Cyclohexene and Bromine Water:
- Straight after reaction:
o clear and colourless liquid
o layer of bubbles hovering in mixture
- During Swirling:
o Cloudy white liquid
- After swirling:
o Fine gas in mixture
o Clear colourless solution
o Big meniscus



Results:

Cyclohexane + Bromine → Bromocyclohexane + Hydrogen Bromide

C6H12 + Br2 → C6H11Br + HBr



Cyclohexene + Bromine → 1,2, dibromocyclohexene

C6H10 + Br2 → C6H10Br2


In alkenes: 2 new ionic bonds form.

If you would like to further research this: use olive oil and sunflower oil
Olive Oil = monounsaturated
Sunflower oil = polyunsaturated

(purposley left out the boring stuff that all the other guys exaplined above)

 

[yoakim]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

Would anyone care enough to answer me this question: Why is it that people use the dynamic equilibrium reaction of bromine water:
Br2 <--> HOBr + H (positive ion) + Br (negative ion)

In some experimental methods, they have infact replaced Br2 with HOBr, thus in their results they have a product of water and hydroxide etc. Is this the wrong approach to this experiment?

 

[phil2010]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

Would anyone care enough to answer me this question: Why is it that people use the dynamic equilibrium reaction of bromine water:
Br2 <--> HOBr + H (positive ion) + Br (negative ion)

This is an example of dynamic equilibrium. As Br2 is only slightly soluble in water most of it stays as Br2 - ie the position of equilibrium lies to the left.

However some of the HOBr reacts with the alkene and according to Le Chatelier as HOBr is removed from the RHS, the forward reatction increases to 'reduce the stress' (of HOBr being removed). This creats more HOBr and uses up Br2. With more HOBr available, this will now react with the alkene. This process continues until the 'equilibrium' lies completely to the RHS which results in the removal of all the brown Br2 - hence the decolourisation of bromine water.

NB - for this to "work" the alkene has to be in excess

 

[tristambrown]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

writing experiments

AIM - what are we trying to prove

Method - Basic rundown of HOW we are going to do it

Procedure - What we did step by step so a 2 yr old can follow it

Results - exact results we got from the experiment (no opinions here just the facts .. eg clear yellow solution turned COLOURLESS for this experiment[nore that colourless is NOT clear ... the solution is always clear - it is at no stage cloudy .. it does however lose its yellow colour)

Conclusion - opinion - therefore results support(or dont) what i was trying to prove in the aim.



As a matter of interest the UV source is not required for this experiment.
The uv simply enables us to see that alkanes can react but that they do this slowly due to the type of reaction that occurs (substitution)

The actual aim of this experiment however is not to "show that alkanes react" but to "compare the reactivity of alkanes with alkenes". This is done in the first part of the experiment when the alkene quickly reacts with the Br2+ ions (addition reaction) and the alkane just sits there NOT reacting - done --- experiment supports the accepted "true" result that alkenes are more reactive than alkanes

 

[mitsui]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

^

my thoughts exactly

 

[yoakim]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

This is an example of dynamic equilibrium. As Br2 is only slightly soluble in water most of it stays as Br2 - ie the position of equilibrium lies to the left.

However some of the HOBr reacts with the alkene and according to Le Chatelier as HOBr is removed from the RHS, the forward reatction increases to 'reduce the stress' (of HOBr being removed). This creats more HOBr and uses up Br2. With more HOBr available, this will now react with the alkene. This process continues until the 'equilibrium' lies completely to the RHS which results in the removal of all the brown Br2 - hence the decolourisation of bromine water.

NB - for this to "work" the alkene has to be in excess

Haha I don't understand anything what you just said.

 

[mitsui]

Re: Need help to write out experiment with chyclohexene and cylcohexane and bromine w

Haha I don't understand anything what you just said.

you dont have to

he /she is just trying to explain why is HOBr in equilbrium

in my school, there are two types, u can do bromine water or simply Br in liquid state