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Edexcel - Chemistry Unit 2 - 4 June 2013

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Reply 360

Priya08

Original post by Priya08

maybe this helps:

Therefore A is an elimination reaction and D is a nucleiophillic sub reaction

Reply 361

Kenzo-k

Original post by Priya08

Therefore A is an elimination reaction and D is a nucleiophillic sub reaction

Yeah but for reaction B theres 2 possible mechanisims depending on whether its a primary or tertiary halogenoalkane C4H9br.. Kinda confused why are there 2 and why does the structuce effect the mechanism?

Reply 362

zyxwvuts

Original post by scientific222

Its been slowly creeping up, it was 63/80 in June 2012 and now 65/80 for Jan 2013's paper (which was real hard in my opinion). That is really insane considering its a paper where mistakes can be made so easily

I too am terrified about grade boundaries.
I hope this paper is very hard so the grade boundaries drop.

Reply 363

doctordee

Going to open a forum for any questions on this so I can answer them all, look out for it.

Reply 364

Priya08

Original post by Kenzo-k

If tertiary the c-br bond breaks, so a carbocation is formed and the OH- nucleiophile attacks the carbocation to form the alcohol

If its primary the OH- nucliophile adds to the halogen alkane first and then the c-br bond breaks

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What state is PI3?

Original post by posthumus

Alkane + Halogen (with UV rays) ----> Halogenoalkane

Halogenoalkane + NaOH -----> Alcohol + NaX

Alcohol + potassium dichromate -----> Carboxylic acid + H2O

[conditions being: dilute H2SO4... heat under reflux]

????? :colondollar:

Yah, nice one. :biggrin:

Reply 367

Priya08

Original post by Jayqwe

What state is PI3?

Aqueous because it is made in moist conditions inorder to produce iodoalkane

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Reply 368

Goods

Original post by HarryMWilliams

The 3 alkyl groups feed their electrons to the carbocation, hence, it forms a much more stable intermediate that primary and secondary alcohols, it's therefore more 'available' to react - the fact theres 3 alkyl groups also means the halogen group can leave easier. That's my understanding at least.

Very good. :biggrin:

But! You're missing a hydrogen in your haloalkane. :tongue:

why you no type 3 why u type 2 only loser type 2... :cool:

Reply 369

Baraf

Original post by HarryMWilliams

I was a bit mean but not that bad, that said, I also hope the June paper is nicer. :tongue:

**January 2013 paper here!**

tnx so much, do you have the answers ?

Reply 370

posthumus

Original post by HarryMWilliams

Yah, nice one. :biggrin:

Just realized someone got it before me, damn it ! :redface:

I was a bit unsure about the second step... because it's not a tertiary alcohol. But I guess it goes under Sn2 mechanism instead anyway :tongue:

Reply 371

phaseshift

Original post by Goods

why you no type 3 why u type 2 only loser type 2... :cool:

Sorry, what?

Original post by Baraf

tnx so much, do you have the answers ?

MS is here: www.thestudentroom.co.uk/attachment.php?attachmentid=203014‎

Original post by posthumus

Just realized someone got it before me, damn it ! :redface:

I was a bit unsure about the second step... because it's not a tertiary alcohol. But I guess it goes under Sn2 mechanism instead anyway :tongue:

It's all the same final product, effectively anyway. :tongue:

Reply 372

Kurraiyo

anyone is clear on what exactly an activated complex is? how does its formation mean a lower activation energy?

Reply 373

Goods

Original post by Kurraiyo

anyone is clear on what exactly an activated complex is? how does its formation mean a lower activation energy?

Its a transition stage that a reaction can occur by, like half breaking the bonds forming the activated complex then breaking the other half for completion. And so it requires less energy than a one stage mechanism

Reply 374

Priya08

Original post by Goods

Is this in the sylabbus?

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Reply 375

SophieL1996

http://www.edexcel.com/migrationdocuments/QP%20GCE%20Curriculum%202000/June%202009/6CH02_01_que_20090603.pdf I don't understand q10 b as I thought it will shift to the right and so increase yield? Thanks :smile:

Reply 376

Goods

Original post by Priya08

Is this in the sylabbus?

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Theres a paragraph about them in reference to SN₂ mechanisms in a chemistry book I have. I don't think we would get a question about it

Reply 377

Priya08

Original post by SophieL1996

3 moles ----> 5 moles

Decreasing the pressure causes EQM to oppose this change and side with the greater moles therefore moves forward

So yield increases but rate decreases as pressure is decreasing and less collision occurs between particles

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