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    hows every1 feeling then lol. for u4 im pretty much sorted except im not 100% on the period 3 / group 4 topic. part from that I think u4 will be pretty good

    U5 i really only started today!! finding it hard - easiest topic being the chemical kinetics, need to go over the benzene stuff as well in much detail, and the transition metals one [ so many colours etc to learn in that one]
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    yeah, that is the annoying part of unit 4...

    unit 5, you should have started before! :P
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    im xact opposite 5 is alrite 4 is B*tch
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    im glad i dont do chemistry anymore lol...edexcel r so stupid...they cram all the exams in within a couple of days...so ur time is limited
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    damn str8...im gonna have wrds with them wen i c em...lol
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    Can anyone explain the distallation boiling curves? Do these come in unit 5 or are they part of synoptic?
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    (Original post by Paxi)
    Can anyone explain the distallation boiling curves? Do these come in unit 5 or are they part of synoptic?
    they are part of the unit 5
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    Okay, for boiling point diagrams - u do two curves (one a reflection of the other but cross at both ends), the bottom one you label liquid, the top one you label vapour. Now how the hell do do those steps to show fractional distillation. I don't understand where you start and which way you go (up in temp or down).

    Is there a melting point composition diagram and is this just a straight line...i get confused, sometimes the lines are straight other times they are curved?! Help!
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    always draw 2 of them curved... Here would be my answer:

    At a given temperature, the vapour has a composition which is richer in the more volatile product (i.e. the one you want to distill off)... When you cool this down, a liquid of new composition is formed, with less of the more volatile compound... If you do this several times, you will eventually release all the more volatile compoun leaving you a solution of the other liquid.. This is basically what happens in fractional distillation, a continuous cycle of heat and then condense and then heat etc...
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    (Original post by rieuwa)
    always draw 2 of them curved... Here would be my answer:

    At a given temperature, the vapour has a composition which is richer in the more volatile product (i.e. the one you want to distill off)... When you cool this down, a liquid of new composition is formed, with less of the more volatile compound... If you do this several times, you will eventually release all the more volatile compoun leaving you a solution of the other liquid.. This is basically what happens in fractional distillation, a continuous cycle of heat and then condense and then heat etc...
    "At a given temperature, the vapour has a composition which is richer in the more volatile product" - this is correct

    the rest of your statement is not correct

    when you condense a vapour the liquid formed will have exactly the same % composition.

    Boiling this new liquid will produce a vapour which is even richer in the more volatile component

    Condensing this produces a liquid richer in the more volatile component etc etc.
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    i am screwed beyond belief
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    read my post carefully - it isn't difficult

    example:

    50% water : 50% ethanol mixture

    produces a vapour with the composition 40% water :60% ethanol

    when this condenses it gives a liquid with the same composition.. to whit

    40% water :60% ethanol

    when this new liquid boils it produces a vapour 30% water : 70% ethanol

    when this condenses it gives a liquid with the same composition.. to whit

    30% water : 70% ethanol

    when this new liquid boils it produces a vapour 20% water : 80% ethanol

    when this condenses it gives a liquid with the same composition.

    The vapour is always richer in the more volatile component than the mother liquor until an azeotrope is reached (at this point the vapour has exactly the same composition as the liquid)
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    apologies... that is what i meant.. i'm sorry if I was confusing... the new LIQUID will have the same composition as the NEW VAPOUR....


    sorry
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    bleh unit4 i think im ready for, i went through past papers and mark schemes so on weird questions you know what sort of answers the examiner is looking for

    on unit5 front im buggered. The transition metal questions are so hard and worded difficultly. And they ask questions on mechanisms i have never seem to have done
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    thanks for the breakdown charco

    i haven't been taught this...does anyone have a link for what this diagram looks like?
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    (Original post by the_wizzz)
    thanks for the breakdown charco

    i haven't been taught this...does anyone have a link for what this diagram looks like?

    yeah, apparently alot of schools didnt bother teaching this part of the syllabus :confused:
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    (Original post by the_wizzz)
    thanks for the breakdown charco

    i haven't been taught this...does anyone have a link for what this diagram looks like?

    check out this link for the vapour pressure - liquid curve with explanation
    vapour - liquid curve as applied to fractinal distillation
 
 
 
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