A question about the effect of no sunlight on cycloalkanes and cycloalkenes (1 Viewer)

Dragonmaster262 · Nov 6, 2009

If any of you have done this practical then can you tell me what will happen if we carry out this investigation in an area of no sunlight. Will it make any difference to the reaction between the hydrocarbons and the bromine water.

Fortify · Nov 6, 2009

Cyclohexane requires UV light to react with Bromine water quicker.

Sarebs · Nov 6, 2009

Yeah, it must be carried out in the dark because the cyclohexane will slowly react with UV light.

Cyclohexene --> Will go clear with or without UV light
Cyclohexane --> Will go clear slowly with UV light

bayan92 · Nov 7, 2009

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[FONT=&quot]e.g. Ethene + Bromine --> 1, 2 – dibromoethane<o></o>[/FONT]

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[FONT=&quot]As mentioned above this is described as an addition reaction because extra elements are being added to the hydrocarbon and breaking the double bond. Alkanes go through a process called a substitution reaction. The substitution needs the presence of UV light to go through.
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[FONT=&quot]<o></o>[/FONT][FONT=&quot]When for example Ethane and Bromine undergo a substitution reaction the compound HBr is formed. This is due to one of the Br being substituted with an H on the hydrocarbon. Therefore Br<sub>2 </sub>is broken into two, one atom goes and joins the hydrocarbon and the H which the Br replaces attaches on to the free Br to make HBr. <o

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Dragonmaster262 · Nov 8, 2009

Is there any particular reason why bromine water is used in this experiment?

Dragonmaster262 · Nov 8, 2009

Hey can someone complete and balance this equation:

C6H12 +Br2 + H20----->?

Dragonmaster262 · Nov 8, 2009

brenton1987 · Nov 8, 2009

Dragonmaster262 said:
Is there any particular reason why bromine water is used in this experiment?

It is coloured.
When it reacts with the alkene it forms a colourless product. The change from coloured to colourless indicates that a reaction has occured.
Whereas if you were going to add water across the double bond, the mixture would start colourless and remain colourless. You cant be certain that anything has happened.

Dragonmaster262 · Nov 9, 2009

bayan92 said:
<link rel="File-List" href="file:///C:%5CDOCUME%7E1%5CBAYANH%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_filelist.xml"><link rel="Edit-Time-Data" href="file:///C:%5CDOCUME%7E1%5CBAYANH%7E1%5CLOCALS%7E1%5CTemp%5Cmsohtml1%5C01%5Cclip_editdata.mso"><style>  </style> [FONT=&quot]Alkenes are more reactive than alkanes due to the presence of their double bond. Alkenes go through what is called an addition reaction. It is where in an alkene; a double bond is broken and replaced with two new covalent bonds added across double bond where a foreign element/compound attaches itself. <o>></o>>[/FONT]
[FONT=&quot] <o>></o>>[/FONT]

[FONT=&quot]e.g. Ethene + Bromine --> 1, 2 – dibromoethane<o>></o>>[/FONT]

[FONT=&quot]<o>> </o>>[/FONT]
[FONT=&quot]As mentioned above this is described as an addition reaction because extra elements are being added to the hydrocarbon and breaking the double bond. Alkanes go through a process called a substitution reaction. The substitution needs the presence of UV light to go through.
[/FONT]
[FONT=&quot]
[/FONT][FONT=&quot]<o>></o>>[/FONT]

[FONT=&quot]<o>></o>>[/FONT][FONT=&quot]When for example Ethane and Bromine undergo a substitution reaction the compound HBr is formed. This is due to one of the Br being substituted with an H on the hydrocarbon. Therefore Br<sub>2 </sub>is broken into two, one atom goes and joins the hydrocarbon and the H which the Br replaces attaches on to the free Br to make HBr. <o>></o>>[/FONT]
[FONT=&quot]<o>> </o>>[/FONT]

Copy pasted directly from Ahmad's Notes.

Dragonmaster262 · Nov 9, 2009

Dragonmaster262 said:
Hey can someone complete and balance this equation:

C6H12 +Br2 + H20----->?

Does anybody know how to do this?

bayan92 · Nov 9, 2009

Dragonmaster262 said:
Copy pasted directly from Ahmad's Notes.

No it isn't. My own practical report. Can be downloaded below.

Bored of Studies - Student online community, resources, notes, past exams, UAI Calculator, ENTER Calculator, HSC, VCE

As for the equation involving water, I have never done it with water.

annabackwards · Nov 9, 2009

Dragonmaster262 said:
Hey can someone complete and balance this equation:

C6H12 +Br2 + H20----->?

Water doesn't react in the equation, it's just the solvent.

C6H12 +Br2-----> Br2C6H10 + H2 --> All aqeous except for H2 which is a gas

If you draw it, the carbons are in a hexagon shape and the above reaction is just an addition reaction, where the 2 Br atoms takes the place of 2 H atoms.

Note that although cyclohexane would react with the bromine with UV light, it takes a very long time so you don't need to do the experiment in a dark room - cyclohexene would react very quickly so you just need to note which one decolourises the bromine water quickly.

Edit: Equation should be C6H12 + Br2 --> C6H12Br2 with all states being aqueous

brenton1987 · Nov 9, 2009

annabackwards said:
Water doesn't react in the equation, it's just the solvent.

C6H12 +Br2-----> Br2C6H10 + H2 --> All aqeous except for H2 which is a gas

If you draw it, the carbons are in a hexagon shape and the above reaction is just an addition reaction, where the 2 Br atoms takes the place of 2 H atoms.

Note that although cyclohexane would react with the bromine with UV light, it takes a very long time so you don't need to do the experiment in a dark room - cyclohexene would react very quickly so you just need to note which one decolourises the bromine water quickly.

Youve drawn a substitution reaction. Your product is still an alkene.

Bromine + alkene is an addition reaction to form an alkane.

C₆H₁₂ + Br₂ --> C₆H₁₂Br₂

Although technically the reaction is:
Br₂ + H₂O --> HBr + HOBr
and both C₆H₁₂Br₂ and C₆H₁₂BrOH are formed.

clintmyster · Nov 9, 2009

brenton1987 said:
Youve drawn a substitution reaction. Your product is still an alkene.

Bromine + alkene is an addition reaction to form an alkane.

C₆H₁₂ + Br₂ --> C₆H₁₂Br₂

Yeah brenton is right. Btw this whole UV stuff tbh is EXTRA knowledge. You actually don't want to talk about UV at all because then your not controlling your variables. The only thing you want to change is the functional group so alkanes/alkenes. The other thing is the aim of the experiment is to distinguish between the reactivities of the two so by exposing to UV light, you won't be able to do this.

annabackwards · Nov 9, 2009

brenton1987 said:
Youve drawn a substitution reaction. Your product is still an alkene.

Bromine + alkene is an addition reaction to form an alkane.

C₆H₁₂ + Br₂ --> C₆H₁₂Br₂

Although technically the reaction is:
Br₂ + H₂O --> HBr + HOBr
and both C₆H₁₂Br₂ and C₆H₁₂BrOH are formed.

I stand corrected; it's been less than a week and i'm forgetting details... at least i remembered that it was an addition reaction XD

Yeah, double bond breaks open and Br2 adds across

iMAN2 · Nov 9, 2009

Dragonmaster262 said:
Is there any particular reason why bromine water is used in this experiment?

As 1, 2-dibromohexane (aq) is clear and so we can see a colour change.

This point isn't as important as knowing why hexane+hexene, cyclohexane+cyclohexene were used:

The hexenes have double bonds (so can react with Br2)
Liquids at room temp
Readily available at school
Cheaper than other hydrocarbons

iMAN2 · Nov 10, 2009

Dragonmaster262 said:
Hey can someone complete and balance this equation:

C6H12 +Br2 + H20----->?

In your title you mention CYLCOhexane and CYCLOhexene.

Thus the equations are as such:

Cyclohexane:
C6H12 (l) + Br2 (aq) ----> C6H12 (l) + Br2 (aq) (No Reaction)

Cylcohexene:
C6H10 (l) + Br2 (aq) ----> C6H10Br2 (aq)

The product is 1, 2-dibromocyclohexane (aq)

For hexane and hexene (an addition reaction):
Hexane:
C6H14 (l) + Br2 (aq) ----> C6H14 (l) + Br2 (aq) (No Reaction)

Hexene:
A critical mistake many people make: Remember, to put 1-hexene or 2-hexene etc (depending on which one you used, we used 1-hexene). As there is a double bond we have to say where in the chain it is located.

brenton1987 said:
C₆H₁₂ (l) + Br₂ (aq) --> C₆H₁₂Br₂ (aq)

Although technically the reaction is:
Br₂ + H₂O --> HBr + HOBr
and both C₆H₁₂Br₂ and C₆H₁₂BrOH are formed.

UV Light and its effects

Dragonmaster262 said:
If any of you have done this practical then can you tell me what will happen if we carry out this investigation in an area of no sunlight. Will it make any difference to the reaction between the hydrocarbons and the bromine water.

UV Light is controlled as the hexanes would undergo a substitution reaction due to the uv light acting as a catalyst, thus invalidating the experiment. Thus, 'NO UV light' is a controlled variable - using aluminium foil to cover and then removing slightly to look at colour change or keeping beakers in shade.

Hexane (with UV as catalyst):

C6H14 (l) + Br2 (aq) ----> C6H13Br (aq) + HBr (g)

Product names: 1-Bromohexane (aq) and Hydrogen Bromide (g)

Cylcohexane (with UV as catalyst):

C6H12 (l) + Br2 (aq) ----> C6H11Br (aq) + HBr (g)

Product names: 1-Bromocylcohexane (aq) and Hydrogen Bromide (g)

Dragonmaster262 · Nov 10, 2009

Isn't bromine water Br2 +H20? Ahmad don't fail me now!

iMAN2 · Nov 10, 2009

Bromine water can be written as Br2 (aqeuous) - meaning dissolved in water. That's all you need, trust me and the many past papers that i've gone through.
So it's Br2 (l) + H20 (l) --> Br2 (aq)

If you really want to go into the depth then use this:
Br2 (l) + H2O (l) --> HBr (aq) + HOBr (aq)

brenton1987 · Nov 10, 2009

iMAN2 said:
So it's Br2 (g) + H20 (l) --> Br2 (aq)

If you really want to go into the depth then use this:
Br2 (g) + H2O (l) --> HBr + HOBr

Br₂_(l) + H₂O_(l) --> Br₂_(aq)
Br₂_(l) + H₂O_(l) --> HBr_(aq) + HOBr_(aq)

A question about the effect of no sunlight on cycloalkanes and cycloalkenes (1 Viewer)

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