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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by Al_Chemist)
    [LIST=1][*]

    An incomplete mark scheme :

    http://www.thestudentroom.co.uk/show....php?t=2372956
    Thank you!
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    For me there was nothing on that paper i didnt know, what's worrying me is my level of response, but i want the following questions cleared up..

    What effect does ir have on bonds?
    It makes polar bonds stretch and vibrate

    Some multiple choice q about ions having increasing covalent character?
    cant remember the exact question but i chose the one where the halogen was the same but the cation was increasing in ionic radii.

    Also another MCQuestion about decomposing to give brown fumes, i chose Lithium nitrate as it decomposes to give NO2 AND Li2O.where as KNO3 decomposes to give only Oxygen

    How to decrease percentage uncertainty?
    I wrote use a lower thiosulphate concentration so larger volume of it is needed

    To see if butan2one has been oxidized you look at an IR spectra and see if absorbtion for OH has disappeared and absorbtion due to C=O becomes visible right.

    And for the CO2 decreasing if more carbonate was in seawater?
    I wrote it would decrease in the atmosphere as more HCO3 would need to be made by getting rid of the excess carbonate, and more CO2 would need to dissolve to replace those lost

    And to show that the reaction in section c was disporportionation did you need to use oxidation numbers? because it said show by using the equation and didnt say anything about redox.

    For CH3F Having higher BP than fluorine did you need to talk about Permanent dipole interactions as they had the same number of electrons.

    and the pcl5 equation made a chloroalkane, POCL3 and HCL with steamy fumes given off as an observation right?

    Thanks guys
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    (Original post by Kurraiyo)
    Ba + 2H2O --> Ba(OH)2 + H2
    Oh ma, for some stupid reason I put it makes barium oxide and hydrogen, instead of barium hydroxide... D: I'm so stupid - how many marks was that? 2?


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    Would placing a piece of paper behind the burrette and reading it off the bottom of the minuscus get the mark for improving accuracy?
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    (Original post by GCSE-help)
    Colourless and Green
    What!?!! I though magnesium was definitely white!
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    For the titration indicator colour, I think I just put colourless, instead of x to colourless...would I still get the mark? I could have sworn it said 'colour at the end point if indicator wasn't used?


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    (Original post by geor)
    The more I think about it the more I think flame test will be accepted. I think by it saying without heat or acid it just meant it wanted you to not put one of the two tests in the previous questions. Terribly worded question if so!


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    I put thermal decomposition instead of the flame test... do you think I would get the marks/
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    (Original post by xstarsx67)
    Oh ma, for some stupid reason I put it makes barium oxide and hydrogen, instead of barium hydroxide... D: I'm so stupid - how many marks was that? 2?


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    You had to include state symbols (I think) too.
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    I thought a flame test counted as heating? Anyway I was very conflicted about that, must have cost me around 7 minutes; I wrote "flame test requires heating" but then went with a solubility test, saying that MgCO3 is somewhat soluble but BaCO3 is not at all soluble.
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    (Original post by mar junior)
    For me there was nothing on that paper i didnt know, what's worrying me is my level of response, but i want the following questions cleared up..

    What effect does ir have on bonds?
    It makes polar bonds stretch and vibrate

    Some multiple choice q about ions having increasing covalent character?
    cant remember the exact question but i chose the one where the halogen was the same but the cation was increasing in ionic radii.

    Also another MCQuestion about decomposing to give brown fumes, i chose Lithium nitrate as it decomposes to give NO2 AND Li2O.where as KNO3 decomposes to give only Oxygen

    How to decrease percentage uncertainty?
    I wrote use a lower thiosulphate concentration so larger volume of it is needed

    To see if butan2one has been oxidized you look at an IR spectra and see if absorbtion for OH has disappeared and absorbtion due to C=O becomes visible right.

    And for the CO2 decreasing if more carbonate was in seawater?
    I wrote it would decrease in the atmosphere as more HCO3 would need to be made by getting rid of the excess carbonate, and more CO2 would need to dissolve to replace those lost

    And to show that the reaction in section c was disporportionation did you need to use oxidation numbers? because it said show by using the equation and didnt say anything about redox.

    For CH3F Having higher BP than fluorine did you need to talk about Permanent dipole interactions as they had the same number of electrons.

    and the pcl5 equation made a chloroalkane, POCL3 and HCL with steamy fumes given off as an observation right?

    Thanks guys
    I thought the multiple choice decomposition question was "what compound decomposes to release only oxygen?", to which it would be KNO3. Otherwise SrNO3 and LiNO3 would be valid answers.

    Other than that I vaguely think you're right.
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    (Original post by sophiekutie)
    What!?!! I though magnesium was definitely white!
    I'm pretty sure it's colourless...


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    (Original post by kevsamuel)
    Would placing a piece of paper behind the burrette and reading it off the bottom of the minuscus get the mark for improving accuracy?
    Hate to say it, but the second bit definitely wouldn't, it should be assumed they are doing so. If they question were, what could be a source of error, that would be a valid answer.

    I think, if I remember properly, I put that you divide the excess into portions, this lowers accuracy, increases reliability, the percentage error increases, but you can eliminate anomalies and take an average.
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    What exactly is heating?

    Heating is provided thermal energy and energy is not transfered into other types, isn't it? So flame test is not heating, its more like excitation of atoms. :confused:

    Or was there other tests. Solubility tests with sodium or ammonium hydroxide? Precipitation test with sulphate ions? pH test? :confused:
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    (Original post by James A)
    You had to include state symbols (I think) too.
    Yeah I think you did, I did include state symbols tho, so *hopefully* I'll get a mark for that...do you think?
    And also the question after where you had to write the equation for Ba(OH)2 reacting with HCL, but obviously I wrote BaO reacting with HCL....do you think I'd get a carry mark for that? (Probably not lol)


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    This is what I put for the carbonate question, is it very very wrong?
    Surely if you added carbonate ions to an equilibrium, the reaction would shift to reverse the change and would restore equilibrium again. There would be the same concentration of carbonate ions as you started with, so the concentration of carbon dioxide in the atmosphere would remain the same.
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    (Original post by geor)
    The more I think about it the more I think flame test will be accepted. I think by it saying without heat or acid it just meant it wanted you to not put one of the two tests in the previous questions. Terribly worded question if so!


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    I agree with this. Why they would make a consented effort to avoid students putting the flame test? It's a valid and very useful test, it's seems stupid the exam board would want us to avoid stating it.
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    (Original post by xstarsx67)
    Yeah I think you did, I did include state symbols tho, so *hopefully* I'll get a mark for that...do you think?
    And also the question after where you had to write the equation for Ba(OH)2 reacting with HCL, but obviously I wrote BaO reacting with HCL....do you think I'd get a carry mark for that? (Probably not lol)


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    Not sure about that I don't think so

    Did the question say barium hydroxide with HCl ?
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    (Original post by Kurraiyo)
    Ba + 2H2O --> Ba(OH)2 + H2
    Hi would it matter if you put multiples?
    Thanks.


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    I wrote for the flame test magnesium producing a bright white flame and barium green...o.O

    Whenever I've done magnesium flame tests in practicals that's what I'd gotten, and it's what the CGP revision guide says...I have no idea what the mark scheme says for magnesium flame colour though, anyone know?
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    Would did you guys put for the equation in section C?
    I did Cl2(g) + 2Br-(aq) --> Br2(aq) + 2Cl-(aq)
 
 
 
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