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    hey people!

    I'm not really looking forward to my Chem HL exam.....but I guess I gotta put up with it...hehe

    Anywayz, I dont get SN1 SN2 mechanisms.....can anybody help out? thnx
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    Hey firestar

    Its really quite simple. I was struggling with it too until I found out that its really much simpler than I thought.

    The mechanism for Primary Halogenoalkanes (one alkyl group attached to the carbon atom bonded to the halogen) is SN2. In an SN2 mechanism, both reactants (the nucleophile and the reactant) must react during the rate determining step. It is bimolecular (This ties into kinetics).
    Example: The reaction between bromoethane and warm dilute NaOH solution.

    C2H5Br + OH- --> C2H5OH + Br-
    The experimentally determined rate expression is: rate = k[C2H5Br][OH-]
    The proposed mechanism involves the formation of a transition state which involves both of the reactants:

    C2H5Br + OH- --> (OH- -- C2H5 -- Br-)- --> C2H5OH + Br-


    The mechanism for Tertiary halogenoalkanes is SN1. For an SN1 mechanism, the step that is the rate determining step is unimolecular, meaning that only one reactant reacts during the rate determining step.
    Example: The reaction between 2-bromo-2-methylpropane and warm dilute NaOH solution.

    C(CH3)3Br + OH- --> C(CH3)3OH + Br-
    The experimentally determined rate expression is: rate = k[C(CH3)3Br]

    A two-step mechanism is proposed that is consistent with the rate expression:

    C(CH3)3Br --slow--> C(CH3)3+ + Br-
    C(CH3)3+ + OH- --fast--> C(CH3)3OH


    I really hope this helps. If you have any other questions, I'd be glad to help as it might help me realize the stuff I need to revise and the stuff I already know.
    Which options are you studying?
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    yeah this chemistry.... i hate organic. Nad we had to take Further org.c h for options... well. At least i will hav 7 days to revise all

    HELP!!
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    Thnx Kraslan...I'^m still kinda struggling with it but I'm sure I'll get it soon

    For options I'm doing Further Organic and Human Biochem....

    There is sooo much to do for the Biochem.....I didnt really understand the iodine index and the Michaelis constant.
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    yeah i hate organic too!

    No problem firestar...We've studied Environmental Chemistry and Fuels & Energy. But I think that Environmental has too much memorization. Thats why im ignoring it and im studying Modern Analytical with a Tutor. Its really much better than any other option...all problem solving, no memorization except for the techniques.
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    (Original post by Firestar)
    Thnx Kraslan...I'^m still kinda struggling with it but I'm sure I'll get it soon

    For options I'm doing Further Organic and Human Biochem....

    There is sooo much to do for the Biochem.....I didnt really understand the iodine index and the Michaelis constant.

    how come u think there is much for biochem?? How about organic?? wiat till thursday, i can explain iodine number 2 you, but right now im really busy...

    What is Michaeliss... i forgot :P Just 2 more days, then i stert studying chem. I have HL...
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    The Michaelis Constant is for Enzyme stuff......
    the vmax stuff......
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    zet no idea what u r talkin about

    so whats the percentage parts of p1, p2, p3 and exercises?
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    If anybody is still struggling with some organic chemistry.
    Theres a really good website on the net that explains it in a lot of clear detail.

    http://www.chemguide.co.uk
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    BOUNDARIES!! EMERGENCY! today my teacher told me about 90% is needed for 7!! LInda help me out!!! Is that true??
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    Your teacher speaks with a fork tongue
    grade break down is:
    24% IA
    20% Paper 1
    30% Paper 3
    Rest% Paper 2

    You need 76% in total to get a 7, but if you get 90% thats extremely impressive- your teacher has high hopes!
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    (Original post by _Shines_)
    You need 76% in total to get a 7
    That is true but not all the time...in May 2003 exam, u needed an 80% to get a 7, thats because the exam was too easy...but you're right, its usually around 76%...but what im trying to say is that it sometimes varies.%
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    thats great! on the mocks i managed to get 61 wizthout studying, so i think it would b enough for 7 with 3 days of non-stop studying and a bit of luck... Yeah my teacher wants to b really sure about it :P
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    61% is not bad. I'm thinking about getting a six. But theres so much stuff I still need to cover. Mainly buffers, and the Options....the options are nasty!
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    Yeah options.. today im gonna study further organic, but then i have to go out with my ex-c-mates cuz we ahve anniversary.. so i wont b able to make some more. But 4 the weeken everything that is left plus biochem... i better get my ass workin!!
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    Here is a question (I don't wanna start a new thread) -

    Do we need to know about how to identify certain ions? like Fe3+ Fe2+ Nitrate ions chloride ions.. etcetc

    I remember doing this in IGCSE I don't know if they assume you know it??
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    if anyone has mark schemes for may 2003 HL, i would greatly appreciate it if you could send them to me [email protected]. My chem teacher ran off the last week of classes and never gave them to me. Also if anyone has any other past chem HL paper that would also help me prep for these blessid test on tuesday. Thank you soo much if anyone is able to do this for me
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    (Original post by akk713)
    Here is a question (I don't wanna start a new thread) -

    Do we need to know about how to identify certain ions? like Fe3+ Fe2+ Nitrate ions chloride ions.. etcetc

    I remember doing this in IGCSE I don't know if they assume you know it??
    You do need to know the colours they can take when in ligands. It is the topic about d-block elements. About group-7 ions, you do need them for identifictation rxn with Ag. They form a precipitate that helps define with what halogen Ag was bound. That is all (I hope ).
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    so guys lets revise 2gether

    AgCl is white, AgBr is creamy and AgI is i think yellow. Or?

    Abotu that d-block elements:

    (just lemme get my book) :P

    ..darn i have no idea! do we only hav to know thise in syllabus?

    would u guys share u knowledge with me
    please
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    Ok.....I need some clarification on the Maxwell-Boltzmann distribution curve.
 
 
 

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