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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    Would we ever be asked to describe an experiment in which we used a titration to find out the concentration of X ?
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    I am suddenly so confused.

    The mechanism of a nucleophilic substitution reaction between halogenoalkane and OH- should be:
    R-X + OH- --> R-OH + X-

    And then it tells you for preparation of halogenoalkane from alcohol is:
    (Eg. Butan-1-ol to 1-bromobutane)
    C4H9OH + HBr --> C4H9Br + H2O

    How come??


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    (Original post by SophieL1996)
    ah thanks how do you do the next part please??
    Wrote it out ... #Dedication <iframe src="https://skydrive.live.com/embed?cid=...HCfo5cFnSiLLZw" width="239" height="319" frameborder="0" scrolling="no"></iframe>
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    (Original post by bhowland1994)
    Wrote it out ... #Dedication <iframe src="https://skydrive.live.com/embed?cid=...HCfo5cFnSiLLZw" width="239" height="319" frameborder="0" scrolling="no"></iframe>
    aw thanks so much! really appreciate it
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    (Original post by leafy9)
    I am suddenly so confused.

    The mechanism of a nucleophilic substitution reaction between halogenoalkane and OH- should be:
    R-X + OH- --> R-OH + X-

    And then it tells you for preparation of halogenoalkane from alcohol is:
    (Eg. Butan-1-ol to 1-bromobutane)
    C4H9OH + HBr --> C4H9Br + H2O

    How come??


    Posted from TSR Mobile
    What do you mean how come?
    I dont' understand your question? Could you rephrase it or be a bit more specific- which part don't you understand?
    OH and H2O can both be used because they both provide a nucleophile, although the OH nucleophile is much stronger.
    Does this help? Post which part you don't understand- will try to help!
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    Q 2,6,, 18 PLEASE http://www.edexcel.com/migrationdocu...e_20100607.pdf
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    suggest how halogenoalkanes cool by change of state.. ? does anyone know the answer to this .. weird weird question\
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    approximately are the grade boundaries low or high for unit 2 chem?
    • Thread Starter
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    2) Those branched ones will have the lowest boiling temperature due to fewer points of contact for london forces. Between them compound Q has the lease amount of electrons, then S has more (due to Br mainly), then again between P & R... P has the least electrons and so on..

    6) D, is not true as when you down group 2... towards Ba very strong heating is required, as they get less polarizing.

    18) m/e will be same, as they both have same amount of Carbons, Hydrogens and Oxygens
    Fragmentation pattern will be different as for example propanal can form CH3CH2 fragment whereas propanone can't
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    what are the most expected questions to come in the exam?
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    What's this type of reaction called?
    C2H6 ---> C2H4 + H2.

    It's not an elimination reaction is it?
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    Q2) D
    Well you know that the compounds with the halogen Br attatched will have the highest b points, and remember that branched molecules have a lower b point that their straight chianed counterparts so using this information you can work out the order
    Q6) D
    Which one does not apply, notice how D says on gentle heating, this isn't true as thermal stability increases down the group so you can assume that carbonates such as RaCO3 and BaCO3 most certainly wont decompose on gentle heating but require large amounts of energy!! Also look at the other options- they are all true so you're only left with D
    Q18) B
    The molecular ion must be the same, if you work yout their molar mass it's the same! Literally just count the number of Cs Os and Hs. But the fragmentation pattern must be different, because if you look at the structural formula, different ion peaks can form eg// there would be a CH2 peak in propanal but not in propanone.
    Does this help? Just post if you need anything extra!
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    Oh and,
    use your knowledge of intermolecular forces to predict the compound with the highest boiling temperature.
    A HF
    B H2O
    C NH3
    D CH4

    Answer is B, water. Why? Doesn't HF have more lone pairs per molecule, and thus more hydrogen bonds?
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    (Original post by Kurraiyo)
    What's this type of reaction called?
    C2H6 ---> C2H4 + H2.

    It's not an elimination reaction is it?
    No, this would be reformation no? from Unit 1?
    Elimination is when an alkene is formed from a haloalkane by reacting it with NaOH in ethanol
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    (Original post by daniya12)
    Q2) D
    Well you know that the compounds with the halogen Br attatched will have the highest b points, and remember that branched molecules have a lower b point that their straight chianed counterparts so using this information you can work out the order
    Q6) D
    Which one does not apply, notice how D says on gentle heating, this isn't true as thermal stability increases down the group so you can assume that carbonates such as RaCO3 and BaCO3 most certainly wont decompose on gentle heating but require large amounts of energy!! Also look at the other options- they are all true so you're only left with D
    Q18) B
    The molecular ion must be the same, if you work yout their molar mass it's the same! Literally just count the number of Cs Os and Hs. But the fragmentation pattern must be different, because if you look at the structural formula, different ion peaks can form eg// there would be a CH2 peak in propanal but not in propanone.
    Does this help? Just post if you need anything extra!
    VERY helpful thanks! are you any good at titrations?
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    PS Reviewer
    (Original post by Kurraiyo)
    Oh and,
    use your knowledge of intermolecular forces to predict the compound with the highest boiling temperature.
    A HF
    B H2O
    C NH3
    D CH4

    Answer is B, water. Why? Doesn't HF have more lone pairs per molecule, and thus more hydrogen bonds?
    H20 can form four hydrogen bonds per molecule, whereas HF can only form two hydrogen bonds per atom. Hence more energy required to separate the water molecules.
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    (Original post by SophieL1996)
    VERY helpful thanks! are you any good at titrations?
    I'll try and help! Send me the questions- will be good practice for me too hah!
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    (Original post by daniya12)
    HF has only one lone pair per molecule whereas water has 2.
    Water has two bond pairs and two lone pairs, HF has one bond pair and THREE lone pairs, right? :/
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    Does anyone have a list of all the reactions we need to know and their conditions etc?
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    (Original post by Kurraiyo)
    Water has two bond pairs and two lone pairs, HF has one bond pair and THREE lone pairs, right? :/
    Yeah! My bad :/
 
 
 
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