OCR Chemistry A F324 Rings, Polymers and Analysis Tue 19 June 2012

Ahh bekhuda hoselam sar rafte, delam gereft!

And I keep thinking about my Eng Lit the day after this and bio!!!!.. :'(

Hey, can anyone help please, I've had a sudden confusion over gas and thin layer chromatography. Do they both separate by adsorption? I thought one separated by relative solubility??


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Yeah that's correct

Arenes undergo electrophilic substitution rather than addition as substitution means that the delocalised ring of electrons is not permanently broken, and the delocalised ring makes benzene more stable so it would want to keep the delocalised ring

Substitution would permanently break the delocalised ring and so substitution is not energetically favourable for arenes

dont freak out!!!

this is all you need to remember:

Chromatography is an analytical technique that separates components in a mixture between a mobile phase and a stationary phase

GC- seperation by adsorption
TLC- seperation by relative solubility

MP(phase that does moves) can be liquid/gas
SP(phase that doesn’t move) can be solid/liquid on a solid support

For TLC the Rf = distance moved by component / distance moved by solvent front

Limitations for TLC: similar components have similar Rf values & unknown compounds have no value for comparison

For GC Retention Time = time taken for compound to pass from column inlet to detector, area under peak is proportional to amount

Limitations for GC: similar compounds have similar retention times, some substances may ‘hide’ under other peaks and unknowns have no ref: RT’s for comparison

Hey thank you for this, but I just looked at jan 2011 question 5 past paper and it says that tlc separates by adsorption?


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SAME. Im just sitting here staring at a page lol.

Ummm I'm finding this quite difficult :/ It's A LOT of memorising to do and my brain is already saturated from F322 and F325 revision.. :/

tlc does separate by adsorption, i think she made a mistake
gc separates by relative solubility and adsorption depending on the stationary phase
if the stationary phase is liquid then it separates via solubility if its solid its absorption

Best way to revise for this paper is to just write all the reactions down in module 1 and 2. I did this, then go over them a couple hours later, just keep doing this and they will stick. Then for module 3 just past papers. Do the examples, its better then reading the book over and over again. good luck

Anyone have the link for jan 2012 paper

For mass spec is every fragment charged? Because ive got here that ch3 is neutral?? :s


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It is not an arene, just a cyclic hydrocarbon with two alkene groups thrown in. As has been mentioned above, it undergoes electrophilic addition, rather than electrophilic substitution, which is what I believe you are describing. A good add-on question would be "Why does this compound react differently to an arene?"

I believe they always have a +?

For this questions 'Why does this compound react differently to an arene?' would you write about cyclohexene having pi eledtrons which are localised between 2 carbon atoms so elctron density increases so molecules are polarised more easily(dipole induced)
whereas benzen is rsisiatnt to bromination because it is more stable it has pi electrons which are delocalised and so electron density is insuffincet, hence cannot induce a dipole in Benzene?? anything else..am i on the right track or no ??