Edexcel Chemistry A2 Unit 5 ~ Wednesday 19th June 2013 (Now Closed) Watch

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posthumus
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(Original post by kabOOmm)
Attachment 224553


pleaseee somebody tell me what the 6 hydrogen environments are and how to get them! this is fro jan 2013. i dont get it. 4 of them are attached to the same environments..
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Mollymod
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(Original post by kabOOmm)
Attachment 224553


pleaseee somebody tell me what the 6 hydrogen environments are and how to get them! this is fro jan 2013. i dont get it. 4 of them are attached to the same environments..
This is what he means.

This is very tough but you need to systematically go through each hydrogen environment and see which are unique to each other. If so, you give them a different environment.
I put my finger on that hydrogen, and look at the species neighbouring it and see if any other hydrogens share that kind of environment.

Environment a is a hydrogen environment unique to itself. There's no other hydrogens bonded to a nitrogen atom in this structure.

Hydrogen environments in b environment. There are 2 of them bonded to the carbon so they 'see' the same thing. No other environments are the same as this one.

Environment c, likewise, is in an environment of its own.
Same as d. There are no other hydrogens that are bonded to the same other species in the overall structure.

Now it gets really tricky. The 'ee' hydrogen environments are the same environment because if you look, the CH2 hydrogens are bonded to a CH on one side, and a CH2 on the other. For the 'ff' hydrogens, it's CH2 and CH on either side of them. It's like a big spider's web that you just have to go through systematically.

It's hard to even mark, so why they made this question, I've no idea.

Hope this helps!
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kabOOmm
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(Original post by Mollymod)
This is what he means.

This is very tough but you need to systematically go through each hydrogen environment and see which are unique to each other. If so, you give them a different environment.
I put my finger on that hydrogen, and look at the species neighbouring it and see if any other hydrogens share that kind of environment.

Environment a is a hydrogen environment unique to itself. There's no other hydrogens bonded to a nitrogen atom in this structure.

Hydrogen environments in b environment. There are 2 of them bonded to the carbon so they 'see' the same thing. No other environments are the same as this one.

Environment c, likewise, is in an environment of its own.
Same as d. There are no other hydrogens that are bonded to the same other species in the overall structure.

Now it gets really tricky. The 'ee' hydrogen environments are the same environment because if you look, the CH2 hydrogens are bonded to a CH on one side, and a CH2 on the other. For the 'ff' hydrogens, it's CH2 and CH on either side of them. It's like a big spider's web that you just have to go through systematically.

It's hard to even mark, so why they made this question, I've no idea.

Hope this helps!


thanks for replying!! but i still dont quite get it. the "ee" and the "ff" hydrogens are both bonded to CH on one side and CH2 on the other. so all 4 of the hydrogen environments, meaning both "ee" and both "ff" are bonded to same things. so why are they divided in to two? shouldn't they be all in the same environment?

@posthumus


im sorry. it opens for me. u can open the one that Mollymod put up
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Mollymod
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(Original post by kabOOmm)
thanks for replying!! but i still dont quite get it. the "ee" and the "ff" hydrogens are both bonded to CH on one side and CH2 on the other. so all 4 of the hydrogen environments, meaning both "ee" and both "ff" are bonded to same things. so why are they divided in to two? shouldn't they be all in the same environment?

@posthumus


im sorry. it opens for me. u can open the one that Mollymod put up
I've drawn it a bit clearer. As you can see, the ee hydrogens are bonded to the HC (the d environment) and to a CH2. The HC (in the d environment) is then directly bonded to the C=O

It's the same thing for the other ee carbon group. It's bonded to that same HC (the d environment), which is bonded to the C=O. It's really all about the neighbouring groups to that environment. They're relative to what's around that hydrogen. If the same 'groups' are around it, then they're the same environment. It's so hard to explain this without sitting there and showing it manually, but here's an illustration showing the ee pathways and the ff pathways.
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(Original post by Mollymod)
I've drawn it a bit clearer. As you can see, the ee hydrogens are bonded to the HC (the d environment) and to a CH2. The HC (in the d environment) is then directly bonded to the C=O

It's the same thing for the other ee carbon group. It's bonded to that same HC (the d environment), which is bonded to the C=O. It's really all about the neighbouring groups to that environment. They're relative to what's around that hydrogen. If the same 'groups' are around it, then they're the same environment. It's so hard to explain this without sitting there and showing it manually, but here's an illustration showing the ee pathways and the ff pathways.


ohh okay so both the "ee" are bonded to the HC in the d environment but the "ff" are bonded to a different HC which is not then directly bonded to a C=O? that's why they are different environments? because one is linked with the C=O and the other isn't?
thanks so much for going to all this trouble! ure the best
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Mollymod
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(Original post by kabOOmm)
ohh okay so both the "ee" are bonded to the HC in the d environment but the "ff" are bonded to a different HC which is not then directly bonded to a C=O? that's why they are different environments? because one is linked with the C=O and the other isn't?
thanks so much for going to all this trouble! ure the best
Yep, exactly.

You've got to look at the bigger picture. What else is bonded to the things that environment is bonded to? That's a really unfair question at the back of a Unit 5 though.

But yeah that's the thing the ee environments have in common. That's what makes them the same environment. The ff are bonded to a different HC, but that different HC is the same for both of the ff carbons. Hence, same environment.
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(Original post by Mollymod)
Yep, exactly.

You've got to look at the bigger picture. What else is bonded to the things that environment is bonded to? That's a really unfair question at the back of a Unit 5 though.

But yeah that's the thing the ee environments have in common. That's what makes them the same environment. The ff are bonded to a different HC, but that different HC is the same for both of the ff carbons. Hence, same environment.

ahhh okay i finally get it now! thankyou so much for your help! the question really threw me off as nmr isn't really a part of unit 5. but then again, it is a synoptic paper.
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Mollymod
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(Original post by kabOOmm)
ahhh okay i finally get it now! thankyou so much for your help! the question really threw me off as nmr isn't really a part of unit 5. but then again, it is a synoptic paper.
Yeah I got 3/4 the first time I did it because I was running out of time/tired, but I was also mixed up on the ff ee's at the end which they throw in to trick you entirely

Definitely not an uncommon thing to drop marks on.
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(Original post by Mollymod)
Yeah I got 3/4 the first time I did it because I was running out of time/tired, but I was also mixed up on the ff ee's at the end which they throw in to trick you entirely

Definitely not an uncommon thing to drop marks on.

i knoww! and by the end you're so exhausted that even if you know you can do the question, chances are you'll probably be out of time! i just hope the june paper is easy..
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(Original post by kabOOmm)
i knoww! and by the end you're so exhausted that even if you know you can do the question, chances are you'll probably be out of time! i just hope the june paper is easy..
Precisely, which is why I always begin with the long answer questions, so I can bag as many marks there as possible. If I lose a couple of multiple choice, that's okay as long as I haven't lost a 10 marker, or a 5 marker question in long answer.
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YAH
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hey, in january 2011 ,question 18 a) ii) can I bromine water as a test or would it form a white ppt?
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posthumus
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(Original post by YAH)
hey, in january 2011 ,question 18 a) ii) can I bromine water as a test or would it form a white ppt?
Yes, as the double bond will turn the bromine water colourless I don't think a white precipitate would be formed though...
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(Original post by YAH)
hey, in january 2011 ,question 18 a) ii) can I bromine water as a test or would it form a white ppt?
Bromine water decolourised, or KMnO4 turns from purple to colourless confirming an oxidation reaction has taken place
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AtomicMan
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Does anyone know why butylamine is a stronger base then ammonia, which is a stronger base than phenylamine?
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(Original post by AtomicMan)
Does anyone know why butylamine is a stronger base then ammonia, which is a stronger base than phenylamine?
Jojo made a beautiful post on this the other day

(Original post by jojo1995)
High pH = alkaline/base

A base is something with the ability to attract a proton

in phenyl amine the nitrogen atom's lone pair of electrons is pulled into the ring of delocalised electrons and so the N atom is less electronegative and so has a weaker abiliuty to attract a proton - so only slightly basic

nh3 has a lone pair of electrons and so is able to attract a proton better than phenylamine as it nitrogen is electronegative so is quite basc


but, butylamine is even stonger .....the nitrogen has methyl groups surrounding it, they are lectron releasing and donate electrons to the nitrogen making it even more electronegative than usual, and so it can attract a proton the easiest and so is the strongest base.

It can't be nice down in hell - so i thought id help you out and try to make your day
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(Original post by posthumus)
Jojo made a beautiful post on this the other day
Why thanks
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AtomicMan
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(Original post by jojo1995)
Why thanks
But can you really say that the nitrogen becomes 'more electronegative'? Since the electronegativity of the nitrogen atom remains the same, if anything you are just changing the delta +ve/-ve charge on the nitrogen atom, rather than making it more electronegative (which describes the ability of nitrogen to attract electrons)?

Thanks for the explanation btw
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F1's Finest
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(Original post by AtomicMan)
But can you really say that the nitrogen becomes 'more electronegative'? Since the electronegativity of the nitrogen atom remains the same, if anything you are just changing the delta +ve/-ve charge on the nitrogen atom, rather than making it more electronegative (which describes the ability of nitrogen to attract electrons)?

Thanks for the explanation btw
electronegativity ≠ delta charge
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(Original post by AtomicMan)
But can you really say that the nitrogen becomes 'more electronegative'? Since the electronegativity of the nitrogen atom remains the same, if anything you are just changing the delta +ve/-ve charge on the nitrogen atom, rather than making it more electronegative (which describes the ability of nitrogen to attract electrons)?

Thanks for the explanation btw

yeah you are right, i shouldn't be describing it as more electronegative ... perhaps 'higher electron density'.
yeah the nitrogen is more delta negative in butylamine than in ammonia... sorry about that and you are welcome

also - chem guide explains it well -

Alkyl groups have a tendency to "push" electrons away from themselves. That means that there will be a small amount of extra negative charge built up on the nitrogen atom. That extra negativity around the nitrogen makes the lone pair even more attractive towards hydrogen ions.

Making the nitrogen more negative helps the lone pair to pick up a hydrogen ion.
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How much of the stuff in the George Facer book is necessary? Do you guys think using CGP and chemguide is enough to do really well in this exam? Help!
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