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    Hi everyone!

    Looking back on my edexcel unit 5, I made quite a few silly mistakes.. Still hoping to get an A, and you're bound to remember the bad parts.. right?

    Anywho, for the free-radical mechanism, I did this (but I drew all Hs etc.):

    (click to enlarge)

    Now, I don't know why I didn't open the C=C bond in the first propagation step, I even though of going back and changing it afterwards, but didn't (partly because the space was all filled up). How much credit do you think I'll get for this though? Maybe one for the initiation, and another because I did eventually open the C=C and get to a point were it could polymerise?

    I can't actually see what's wrong with the mechanism though.. I'm fairly sure it's not what they were looking for, and it's less likely to happen, but because it still makes sense, maybe I'll even be ok?
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    Is A-Level Chem hard?
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    (Original post by Don Corleone)
    Is A-Level Chem hard?
    depends if u are gud at memorisin...not much understanding needed at this level ...but the ability to rote learn is a necessity
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    So no ideas about the marking of my mechanism?
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    (Original post by mr_shoe_uk)
    Hi everyone!

    Looking back on my edexcel unit 5, I made quite a few silly mistakes.. Still hoping to get an A, and you're bound to remember the bad parts.. right?

    Anywho, for the free-radical mechanism, I did this (but I drew all Hs etc.):

    (click to enlarge)

    Now, I don't know why I didn't open the C=C bond in the first propagation step, I even though of going back and changing it afterwards, but didn't (partly because the space was all filled up). How much credit do you think I'll get for this though? Maybe one for the initiation, and another because I did eventually open the C=C and get to a point were it could polymerise?

    I can't actually see what's wrong with the mechanism though.. I'm fairly sure it's not what they were looking for, and it's less likely to happen, but because it still makes sense, maybe I'll even be ok?
    I don't do Edexcel but i don't really understand why you drew the chemicals like that...

    For AQA i just had to write them out like this when the question asks for a mechanism... i've never had to actually draw the chemicals out:

    E.g. Reaction of an alkane with chlorine

    Initiation:

    Cl2 --> 2Cl.

    Propigation:

    CH3CH3 + Cl. --> CH3CH2. + HCl

    Termination:

    CH3CH2. + Cl. --> CH3CH2Cl


    There are many reactions and so you can get a great variety of products since CH3CH2. can be used again in the propigation stage again

    Btw, i really don't understand the reason why you think that you need to open the C=C bond in order for an addition polymerisation reaction... it's just...

    n CH2=CH2 --> [-CH2-CH2-] n
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    I think it probably did want a proper drawn out mechanism, as it even asked for the correct arrows to show electron movement. Maybe that's something more focused on by edexcel.

    Btw, i really don't understand the reason why you think that you need to open the C=C bond in order for an addition polymerisation reaction... it's just...

    n CH2=CH2 --> [-CH2-CH2-] n
    ..That has had the double bond opened though? You need it to happen at some point in the mechanism, and I probably should've done it first, just wondering how much credit I still might get.
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    well... that's not on my board then either
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    The main problem is u still have a double bond in your polymer chain (cos it remains from the first propogation step). I can't remember how many marks it was worth, but u will def get the initiation. Sorry to be harsh, but I think you would be lucky to get either of the propogations, since none of them are entirely correct. I suppose if they allow carry through marks, u might only get penalised for the first propogation - since this led to an incorrect second propogation stage - its always hit and miss as to when carry through marks are allowed though.
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    i remember the question asked you be clear on your use of arrows, i.e. using half arrows, so i think you could get a mark for that.
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    (Original post by Revenged)
    I don't do Edexcel but i don't really understand why you drew the chemicals like that...

    For AQA i just had to write them out like this when the question asks for a mechanism... i've never had to actually draw the chemicals out:

    E.g. Reaction of an alkane with chlorine

    Initiation:

    Cl2 --> 2Cl.

    Propigation:

    CH3CH3 + Cl. --> CH3CH2. + HCl

    Termination:

    CH3CH2. + Cl. --> CH3CH2Cl


    There are many reactions and so you can get a great variety of products since CH3CH2. can be used again in the propigation stage again

    Btw, i really don't understand the reason why you think that you need to open the C=C bond in order for an addition polymerisation reaction... it's just...

    n CH2=CH2 --> [-CH2-CH2-] n
    The question on thursday asked for half-headed arrows to show movement of electrons so we had to show the whole molecule
 
 
 
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