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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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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?
    You make it into a halogenoalkane using free radical substation and then use NaOH in ethanol to make the alkene.


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    (Original post by daniya12)
    I'll try and help! Send me the questions- will be good practice for me too hah!
    http://www.edexcel.com/migrationdocu...e_20100121.pdf q19 b ii thanks
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    (Original post by James A)
    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.
    ok, water forms four hydrogen bonds: two of its hydrogen atoms bond to other water molecules, and two other hydrogen atoms bond to this water molecule. right?

    if that's the case, then HF should also form four bonds considering it has one bond pair and three lone pairs?
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    (Original post by daniya12)
    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!
    Well, I don't understand how a halogenoalkane can be made from an alcohol in a somewhat opposite reaction of how an alcohol is made from a halogenoalkane.


    Eg. Butan-1-ol and 1-bromobutane

    C4H9Br + H2O/OH- --> C4H9OH + HBr/Br-

    C4H9OH + HBr --> C4H9Br + H2O

    I just really don't understand how both these reactions are possible since they seem to be opposite in nature.



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    (Original post by Kurraiyo)
    ok, water forms four hydrogen bonds: two of its hydrogen atoms bond to other water molecules, and two other hydrogen atoms bond to this water molecule. right?

    if that's the case, then HF should also form four bonds considering it has one bond pair and three lone pairs?
    I think water has 3 hydrogen bonds. The oxygen with some hydrogen and the 2 hydrogens with two other oxygens. Whereas HF only has 2.


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    do we need to know the reaction between halogenoalknae and water? like the drawing?
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    (Original post by Kurraiyo)
    ok, water forms four hydrogen bonds: two of its hydrogen atoms bond to other water molecules, and two other hydrogen atoms bond to this water molecule. right?

    if that's the case, then HF should also form four bonds considering it has one bond pair and three lone pairs?
    Have to consider that the HF is only forming bonds with other HF molecules so that each one can only form 2 hydrogen bonds as otherwise there wouldn't be enough hydrogens to go round.
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    (Original post by Kurraiyo)
    ok, water forms four hydrogen bonds: two of its hydrogen atoms bond to other water molecules, and two other hydrogen atoms bond to this water molecule. right?

    if that's the case, then HF should also form four bonds considering it has one bond pair and three lone pairs?
    http://uk.answers.yahoo.com/question...2045307AAgsFvH

    Read the second answer down by greendawn.
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    Ok, so given the information on the question, we can work out the number of moles of sodium thiosulphate using (moles = conc x volume) = 0.1 x 12.6/1000 = 0.00126

    Now look at the equation given right at the top, and look at the stochiometery (mole ratio) of iodine: sodium thiosulphate , you'll see its 1:2 (it almost always is 1:2 for this reaction)
    and then you divide/multiply accordingly, so in this case we would divide by two, so moles = 0.00063

    Does this help?
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    (Original post by leafy9)
    I think water has 3 hydrogen bonds. The oxygen with some hydrogen and the 2 hydrogens with two other oxygens. Whereas HF only has 2.


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    water can form 4 as it has 2 lone pairs
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    (Original post by daniya12)
    Ok, so given the information on the question, we can work out the number of moles of sodium thiosulphate using (moles = conc x volume) = 0.1 x 12.6/1000 = 0.00126

    Now look at the equation given right at the top, and look at the stochiometery (mole ratio) of iodine: sodium thiosulphate , you'll see its 1:2 (it almost always is 1:2 for this reaction)
    and then you divide/multiply accordingly, so in this case we would divide by two, so moles = 0.00063

    Does this help?
    yes thanks, how do you do the next bit please?
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    (Original post by James A)
    http://uk.answers.yahoo.com/question...2045307AAgsFvH

    Read the second answer down by greendawn.
    I get it now! Thank you very much !
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    (Original post by James A)
    http://uk.answers.yahoo.com/question...2045307AAgsFvH

    Read the second answer down by greendawn.
    I've read in mark schemes however that Hydrogen can form 2 hydrogen bonds per molecule :confused:
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    (Original post by James A)
    Who told you that sulfur is +1 then?

    It depends what the question tells you tbh.
    In a multiple choice, it asked exactly that, but gave no additional info. I assumed Na would be +1


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    (Original post by Tuya)
    In a multiple choice, it asked exactly that, but gave no additional info. I assumed Na would be +1


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    In that case of course, then sodium would have to be +1.

    But if they don't tell you info like that, then you would assume sodium is +1!
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    (Original post by James A)
    In that case of course, then sodium would have to be +1.

    But if they don't tell you info like that, then you would assume sodium is +1!
    I got it wrong though... The answer was -2 for some reason


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    (Original post by Tuya)
    I got it wrong though... The answer was -2 for some reason


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    Sorry my bad... -2 is for sulphur which is what they asked for, I didn't read it right... Lol sorry.


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    (Original post by adi19956)
    Mostly, but not always. Eg in NaHS the oxidation number of sodium is -2. I have no idea why though.
    What nonsense. Na has oxidation state +1, H has oxidation state +1, S has oxidation state -2. HS- is a well-known anion; imagine having H2S in solution, it dissociates once and what do you get? HS-. This isn't some mystical compound we're dealing with. It's very standard.

    Group 1 and (I think) Group 2 will always have oxidation state +1 and +2 respectively. That's the first rule of deciding oxidation states, and the whole system of working them out is a theoretical game rather than based on reality so there's no point debating it. So let me say it again: Group 1 and (I think) Group 2 will always have oxidation state +1 and +2 respectively.
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    (Original post by James A)
    In that case of course, then sodium would have to be +1.

    But if they don't tell you info like that, then you would assume sodium is +1!
    Do you know which experimental set-ups we need to know? We need heat under reflux, distil in situ and alcohol dehydration, anything else?
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    Can anyone please tell what do we have to know about carbon nanotubes ?
 
 
 
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