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hardest topics in a level chem watch

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    :confused: ok guys i got unit 4 and unit 5 on thursday for edexcel chem, i was wondering what ppl find the hardest topics so i could try to see what i should spend most time on, i really am feeling guilty as my brain is telling me that i know it all but i bet i dont, im really in a quandry!
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    Buffer equation
    Organic reactions - not hard but need to know them
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    ok lets see if i got it right :

    ph =pka - log of the concentration of the acid over the conc of the base

    ??
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    (Original post by ravs)
    ok lets see if i got it right :

    ph =pka - log of the concentration of the acid over the conc of the base

    ??
    Sounds right to me
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    How about, nitration of benzene?
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    (Original post by ravs)
    :confused: ok guys i got unit 4 and unit 5 on thursday for edexcel chem, i was wondering what ppl find the hardest topics so i could try to see what i should spend most time on, i really am feeling guilty as my brain is telling me that i know it all but i bet i dont, im really in a quandry!
    ok well iv been revising them alot
    it just depends on you and what you find easier
    are you better on the theory side of chemistry or the maths?
    personally im better on the maths side so i tend to study the theory more, kp and kc and logs and stuff like that i dont need to study.
    stuff like transition metals and organic chemistry i need time to study that!
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    nitration of benzene

    hno3 + 2h2so4 goes to no2+ + h30+ + 2hso4-

    then the ring attacks the no2+, and u get a ring with a C+ in it with H and the no2 attacthed, the H donates the electron pair back to benzene giving u nitrobenzene



    he says nervously
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    (Original post by ravs)
    nitration of benzene

    hno3 + 2h2so4 goes to no2+ + h30+ + 2hso4-

    then the ring attacks the no2+, and u get a ring with a C+ in it with H and the no2 attacthed, the H donates the electron pair back to benzene giving u nitrobenzene



    he says nervously
    correct
    you should stick to learning theory i think
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    (Original post by ravs)
    ok lets see if i got it right :

    ph =pka - log of the concentration of the acid over the conc of the base

    ??
    shouldn't it be, pH = pKa - log [SALT]/[acid]
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    i have learnt it as:

    Ka = ([H+][A-] )/ [AH]

    and then pH = -log10[H+]

    where AH is the weak acid, and A- is the conjugate base. Probably the same thing.

    i find trends and patterns quite difficult - knowing the structure of the different compounds. like which ones are ionic lattice and which are simple covalent etc. it just seems so random and un-necessary
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    (Original post by noggin)
    i have learnt it as:

    Ka = [H+][A-]
    [AH]

    and then pH = -log10[H+]

    where AH is the weak acid, and A- is the conjugate base. Probably the same thing.
    thats exactly how i learnt it
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    (Original post by kriztinae)
    thats exactly how i learnt it
    goodo, i was starting to get worried then!! did you also learn for weak acids to find pH you have to do....

    Ka = ([H+]^2)/[AH]

    and then pH = -log10 [H+]

    ?
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    (Original post by noggin)
    goodo, i was starting to get worried then!! did you also learn for weak acids to find pH you have to do....

    Ka = ([H+]^2)/[AH]

    and then pH = -log10 [H+]

    ?
    for weakacids its
    ka = [H+] [A-] / [HA] where [H+] = [A-]
    but yes yours is correct!
    i need to look up buffer questions!

    and ph is correct, dotn forget to put aq in brackets like this
    ph = -log10[H+(aq)].......... or to be more precise its -log[H3O+(aq)]
    but i doubt it make much of a difference!
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    (Original post by ravs)
    :confused: ok guys i got unit 4 and unit 5 on thursday for edexcel chem, i was wondering what ppl find the hardest topics so i could try to see what i should spend most time on, i really am feeling guilty as my brain is telling me that i know it all but i bet i dont, im really in a quandry!
    ORGANIC ON BOTH UNITS.. hate this topic!!!
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    im about 90% certain its concentration of acid over concentraion of base for the buffer calculation
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    (Original post by kriztinae)
    ph = -log10[H+(aq)].......... or to be more precise its -log[H3O+(aq)]
    We're not even meant to know that much, and it isn't even that, it's actually H9O4+(aq)
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    (Original post by Golden Maverick)
    We're not even meant to know that much, and it isn't even that, it's actually H9O4+(aq)
    thanx!
    well my teacher did always teach me what i didnt need to know as opposed to what i did need to know! hmm glad its over!
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    dose anyone find group 4 and period 3 hard?
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    (Original post by ravs)
    dose anyone find group 4 and period 3 hard?
    yes me!
    i hate learning trends and stuff like that
    thenthe equations i hate it
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    i know it sucks eternal c*ck.

    i pray that we get 2 easy papers i really do
 
 
 
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