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does a branched chain affect boiling point? if so how and why? thanks :)

eg. a branched alcohol or alkane

thank you :smile:

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Reply 1
basically as branched chains increase there will be fewer contact points, therefore less van der waals, meaning there is less energy required to break the forces leading to a lower boiling point
Yes. Branched chains implies less contact points, so less Van der Waals forces in-between molecules.
So less energy/lower temperature is needed to break/overcome them.
I'm wondering now if you can say that hydrogen bonding is also less in the case of alcohols. Is there less contact between OH groups in a branched chained alcohol?
Original post by TARS
Oh dear silly silly answers, stop abusing chemistry.

Branched molecules prevents the close approach of molecules. Given that Van der Waals' dispersion forces are exerted over a small range, the magnitude of these intermolecular forces is smaller, so less energy is required to overcome these forces - giving rise to lower boiling points.


So essentially, you have literally just said exactly what they just said but with a slightly more 'sophisticated' use of english language. The answer they have given the OP is pretty much word perfect to that required by UK exam boards for A-level.
Reply 5
Original post by Hinicetomeetyou
So essentially, you have literally just said exactly what they just said but with a slightly more 'sophisticated' use of english language. The answer they have given the OP is pretty much word perfect to that required by UK exam boards for A-level.


Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".
Reply 6
By having branched chains, this means the molecule will be smaller therefore there will be fewer VdW needed to overcome
Original post by TARS
Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".


Thanks for that misrepresentation.
Original post by TARS
And how many A*s did you get at GCSE?


I didn't bother take them GCSEs...

Seriously though, being slightly mathematically minded, I thought it originally better to say that branched chained hydrocarbons have less surface area or less contact area, but I was told by my chemistry teachers to say less contact points. Marking depends more on the mark scheme than on how examiners feel.
My answer does mention VDW 'in-between molecules', so I'm fine.
(edited 8 years ago)
Original post by TARS
Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".


You keep telling yourself that buddy :smile: I'm so glad my small mind has completed this exam already. Shame about you not having finished AS yet. And Interests in people's mothers at 17. Top banter lad :wink:
Original post by TARS
Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".


I used to teach AQA. I have examined for Edexcel. I am currently an examiner for OCR A F322 and F325. I will be writing questions for one of the new OCR A papers and will be reviewing a paper for OCR B.

This, and every other examiner, would award full marks for something vague like "branching implies less contact." if it were given at A-level.
Original post by TARS
Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".


The marks are awarded for: branched chains have less surface contact so have less Van der Waal so less energy is needed to break them (for OCR anyway). Stop trying too hard to look intelligent.
Reply 12
Original post by TARS
Sorry if I'm being too pedantic for your small mind, but that sophistication is what guarantees you marks. An examiner will almost certainly award no marks for something as vague as "branching implies less contact".


Actually being less sophisticated doesn't mean no marks are awarded... It's the same content


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Reply 13
Original post by TARS
Explain to me how the fact that you've finished AS exams makes you better than me. By that logic, everyone who is older than you is better than you - what a shameful thought, knowing that you're nowhere near the top. Relatively speaking that would put us at roughly the same place.



Full marks for that solitary statement? You do realise that these are often three mark questions.



Stop trying to look hard? I'm trying to help this person who cannot read a book.


I'm actually 14 and doing National 5 chemistry in Scotland I was just curous as I noticed it in the data book... trust me I'm perfectly capable of reading a book

thanks for your help anyway
Reply 14
Original post by rend
basically as branched chains increase there will be fewer contact points, therefore less van der waals, meaning there is less energy required to break the forces leading to a lower boiling point


Original post by EricPiphany
Yes. Branched chains implies less contact points, so less Van der Waals forces in-between molecules.
So less energy/lower temperature is needed to break/overcome them.


Original post by EricPiphany
I'm wondering now if you can say that hydrogen bonding is also less in the case of alcohols. Is there less contact between OH groups in a branched chained alcohol?


Original post by Hinicetomeetyou
So essentially, you have literally just said exactly what they just said but with a slightly more 'sophisticated' use of english language. The answer they have given the OP is pretty much word perfect to that required by UK exam boards for A-level.


Original post by 9clpc9
By having branched chains, this means the molecule will be smaller therefore there will be fewer VdW needed to overcome


Original post by Pigster
I used to teach AQA. I have examined for Edexcel. I am currently an examiner for OCR A F322 and F325. I will be writing questions for one of the new OCR A papers and will be reviewing a paper for OCR B.

This, and every other examiner, would award full marks for something vague like "branching implies less contact." if it were given at A-level.


Original post by katemate98
The marks are awarded for: branched chains have less surface contact so have less Van der Waal so less energy is needed to break them (for OCR anyway). Stop trying too hard to look intelligent.


Original post by A.F
Actually being less sophisticated doesn't mean no marks are awarded... It's the same content


Posted from TSR Mobile



thanks for your help everyone :smile: :biggrin:
Reply 15
Original post by TARS

Stop trying to look hard? I'm trying to help this person who cannot read a book.

Original post by katemate98
Stop trying too hard to look intelligent.



she said stop trying too hard to look intelligent
not stop trying to look hard

it seems there is more than one individual here who cannot read :P :L

thanks again everyone :smile:
(edited 8 years ago)
Original post by TARS



Stop trying to look hard? I'm trying to help this person who cannot read a book.


I said ''stop trying too hard to look intelligent''. Maybe you should learn to read yourself.
Original post by TARS
Explain to me how the fact that you've finished AS exams makes you better than me. By that logic, everyone who is older than you is better than you - what a shameful thought, knowing that you're nowhere near the top. Relatively speaking that would put us at roughly the same place.



First of all, I never said I was better than you; I simply stated that I have done this exam and you have not, so I would like you to write what you think is the perfect chemistry in your exam and see where it lands you.
Second of all, you pretty much have the whole forum against you right now because you are acting like an arrogant little brat, give up now; you've been told by an examiner/teacher, numerous other students, and yes, I respect those older than me..those who have gone on to do chemistry degree's tend to be more likely to know the right answer than me; I put good faith in chemistry teacher's at my school and equally in the one who just slated your answer.
Original post by TARS
yeah it was a test to see if you were worth talking to ... people always focus on the language you use and try to use it as a weapon and the discussion becomes counterproductive - I use it commonly to determine whether or not someone is worth discussing with, you are obviously not, goodbye


Take notes people; this is exactly how you admit that you're wrong in the dignified way.
Original post by TARS
yeah it was a test to see if you were worth talking to ... people always focus on the language you use and try to use it as a weapon and the discussion becomes counterproductive - I use it commonly to determine whether or not someone is worth discussing with, you are obviously not, goodbye


Lmfaoooo I'll give you credit for coming up with that story so quickly, good one :smile:

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