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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

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    7 Consider the following organic liquids:
    A ethanal
    B ethanol
    C tetrachloromethane
    D
    trichloromethane
    d) Which liquid has an infrared spectrum with a broad absorption due to hydrogen


    bonding?
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    does anyone know why the best solvent for cyclohexanol is CH3COCH3 and not water?
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    A CH3CH3 CH2 CH2 + H2


    B nCH2 CH2 ( CH2 CH2 ) n


    C CH2 CH2 + HBr CH3CH2Br


    D CH3CH2Br + H2O CH3CH2OH + HBr
    (d) Which reaction requires an initiator?

    (1)





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    A CH3CH3 CH2 CH2 + H2
    B nCH2 CH2 ( CH2 CH2 ) n
    C CH2 CH2 + HBr CH3CH2Br
    D CH3CH2Br + H2O CH3CH2OH + HBr which requires an initiator what is it?
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    (Original post by marseille_h)
    Ok thanks so we don't need to know why i thought it might be related to the charge or something :rolleyes:
    Nerd that I am this is not the sort of thing I spend my free time learning. Nonetheless something like this can only have one explanation - thermodynamics. It's just unfavourable to dissolve certain compounds and not others. For the sulphates and carbonates you should probably just say the bonds are stronger because there is less polarization (due to the cation being larger and polarization being related to charge density=z/r) down the Group. Why this doesn't work for hydroxides, I have my own vague theories but it should be on the net if you're interested

    (Original post by own)
    Okay, just regurgitating what I have learned from cgp, what has become like a bible to me now. Shall remember that though, thanks
    Haha
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    part a) is B
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    And b) is A
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    Ok guys, would someone PLEASE enlighten me about which apparatus (reflux or distillation) to use when preparing a halogenoalkane? It is causing a lot of confusion. I would really appreciate some help, thanks.
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    (Original post by charlieejobson)
    does anyone know why the best solvent for cyclohexanol is CH3COCH3 and not water?
    water is polar and as you know, it is hard for a non-polar solute to dissolve in a polar solvent and vice versa. Just remember that like dissolves like.
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    (Original post by PickwickianGeek)
    water is polar and as you know, it is hard for a non-polar solute to dissolve in a polar solvent and vice versa. Just remember that like dissolves like.
    okay thank you and is other one non- polar?
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    (Original post by SophieL1996)
    6 For parts (a) and (b), use your knowledge of intermolecular forces to predict the

    compound with the highest boiling temperature.

    (a) A HF

    B H2O

    C NH3

    D CH4

    (1)

    (b) A 1-iodobutane

    B 1-chlorobutane

    C 2-methyl-2-iodopropane

    D 2-methyl-2-chloropropane
    Water can form 2 hydrogen bonds per molecule therefore has highest boiling point

    next one... linear has most points of contact therefore either A or B.. Iodine has more electrons than chlorine (greater london forces) therefore it's B


    (Original post by Big-Daddy)
    They are the mechanisms of elimination. We only deal with leaving groups (e.g. X-) and that too only with E2 according to geor in the post above. Difference is that E2 is what usually happens when there is little alkyl substitution on the nearby C atoms, E1 when there is lots.

    Want more details? Look it up!
    Pretty confused Never come across 2 types of mechanisms for Electrophilic substitution
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    (Original post by GCSE-help)
    Ok guys, would someone PLEASE enlighten me about which apparatus (reflux or distillation) to use when preparing a halogenoalkane? It is causing a lot of confusion. I would really appreciate some help, thanks.
    http://www.knockhardy.org.uk/ppoints.htm

    Take a look at the powerpoint for halogenoalkanes
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    (Original post by GCSE-help)
    Ok guys, would someone PLEASE enlighten me about which apparatus (reflux or distillation) to use when preparing a halogenoalkane? It is causing a lot of confusion. I would really appreciate some help, thanks.
    Apart from forming ethanal, I think in unit 2.... all others are heat under reflux
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    (Original post by GCSE-help)
    Ok guys, would someone PLEASE enlighten me about which apparatus (reflux or distillation) to use when preparing a halogenoalkane? It is causing a lot of confusion. I would really appreciate some help, thanks.
    First you need to heat all the reactants under reflux for about 30 minutes. This is to ensure that as much of the reactants are converted into products. After this you set up a distillation apparatus, you'll collect two layers: an organic layer and an aqueous layer. The one with the lower density is on top (you'll get the densities in the question). Discard the aqueous layer and redistillate the organic layer once again, collect at the boiling point of the halogenoalkane to obtain the pure product.
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    (Original post by charlieejobson)
    okay thank you and is other one non- polar?
    Yes, that's correct.
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    (Original post by posthumus)
    Pretty confused Never come across 2 types of mechanisms for Electrophilic substitution
    This isn't on our syllabus.

    But I guess I should try to undo the damage I've done. It's elimination, first of all. Just as we have SN1 and SN2, we have E1 and E2. If you want to know how to draw them, you will obviously have to look it up. But the mechanism you know, for elimination, is E2. (Presumably)
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    (Original post by posthumus)
    Water can form 2 hydrogen bonds per molecule therefore has highest boiling point

    next one... linear has most points of contact therefore either A or B.. Iodine has more electrons than chlorine (greater london forces) therefore it's B




    Pretty confused Never come across 2 types of mechanisms for Electrophilic substitution
    if iodine has more electrons should it haave a high boiling point??
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    PS Reviewer
    What's all this E1 and E2 business?

    This ain't in the spec, so no point trying to even discuss it.
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    jan 2011 paper 14c(ii)draw a diagram of the apparatus you would use to prepare ethanal from ethanol in the lab and collect the product....help, what would I draw??
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    (Original post by Big-Daddy)
    This isn't on our syllabus.

    But I guess I should try to undo the damage I've done. It's elimination, first of all. Just as we have SN1 and SN2, we have E1 and E2. If you want to know how to draw them, you will obviously have to look it up. But the mechanism you know, for elimination, is E2. (Presumably)
    (Original post by geor)
    This is the mechanism! (and it's elimination by the way haha)
    http://www.chemguide.co.uk/mechanism.../elim.html#top
    Ah I see, not in this unit ! But it is in Unit 4 :/ Which I need to start preparing for straight afterwards damn it

    Thanks!

    (Original post by SophieL1996)
    if iodine has more electrons should it haave a high boiling point??
    Yes that's correct, and sorry did the question ask for lowest boiling point ??
 
 
 
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