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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by GCSE-help)
    Guys let's end this once and for all, is a C-H bond polar or not? I thought Ethane wasn't a polar molecule simply because there is not difference in electronegativity between Carbon and Hydrogen (or an insignificant difference)
    Yes it is polar. There is no "difference in electronegativity is insignificant". If there is a difference, at all, there is a bond dipole moment and the bond is polar. The reason why ethane is non-polar is because the bond dipole moments cancel out leavng no net dipole moment; the easy way to think of this is as ethane being symmetrical and having all atoms substituent atoms H being the same on each central atom (where the central atoms C are the same as each other). If any of these atoms were different, symmetry would not make a difference; the net dipole moment would not be 0.
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    (Original post by Matterhorn)
    Okay but surely if it can be 0.06 above or 0.06 below then the overall uncertainty is 0.12 as it could be anywhere within this range. I agree about what you say about doubling for two readings but I'm pretty sure if the answer didn't have a plus or minus the answer would be 0.48 %


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    No, think about it like this I can either say generally I am 2m away from you or I could say i am either 2m in this or that direction. The displacement is 2m either way.


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    1-iodobutane reacts with hot aqueous silver nitrate solution. Describe what you
    would see when this reaction takes place. In this reaction, does the water act as a neucophile?
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    Anyone else having trouble remembering trends!?
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    (Original post by Hi, How are you ?)
    1-iodobutane reacts with hot aqueous silver nitrate solution. Describe what you
    would see when this reaction takes place. In this reaction, does the water act as a neucophile?
    You'll get AgI ... which is a yellow precipitate
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    (Original post by Hi, How are you ?)
    1-iodobutane reacts with hot aqueous silver nitrate solution. Describe what you
    would see when this reaction takes place. In this reaction, does the water act as a neucophile?
    Water acts a a nucleophile and displaces the halogen halide. The halide reacts with the silver ion to form a yellow precipitate


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    Can anyone answer part b for me with an explanation please?
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    (Original post by Hi, How are you ?)
    so say if you had a cl free radical, and it reacts with an ozone molecule, it makes a ClO* free radical, so how does it then forms other free radicals if it reacts with a oxygen free redial to make O2 and Cl*?
    The ClO* can then react with O2 to make Cl* and O3.

    Or it could react with O* to form O2 and Cl*
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    (Original post by Matterhorn)
    Okay but surely if it can be 0.06 above or 0.06 below then the overall uncertainty is 0.12 as it could be anywhere within this range. I agree about what you say about doubling for two readings but I'm pretty sure if the answer didn't have a plus or minus the answer would be 0.48 %


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    Look at it this way, (this is why i love maths)

    The worst reading you can have is either 25.06 or 24.94 ..agreed?

    so the uncertainity would be (25.06-25.00)/25.00 =2.4 x10^-3

    the other one would be (24.94-25.00)/25.00 = -2.4 x10^-3

    Both of which are 0.24 % and they are either + or -

    understand now :P
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    In CGP it says Phenolphthalein goes from red to colourless but in the mark scheme it says colourless to red
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    (Original post by Matterhorn)
    Okay but surely if it can be 0.06 above or 0.06 below then the overall uncertainty is 0.12 as it could be anywhere within this range. I agree about what you say about doubling for two readings but I'm pretty sure if the answer didn't have a plus or minus the answer would be 0.48 %


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    That's correct
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    (Original post by marseille_h)
    In CGP it says Phenolphthalein goes from red to colourless but in the mark scheme it says colourless to red
    It depends on whether you are adding an acid or an alkali


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    (Original post by Goods)
    Water acts a a nucleophile and displaces the halogen halide. The halide reacts with the silver ion to form a yellow precipitate


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    Water doesn't act as a nucleophile, but the OH breaks off the water, which uses it's lone pair to attack the delta positive carbon. (this is what displaces the halide)
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    (Original post by Gnome :))
    Yes, the overall percentage error would be 0.48%, however look at the answers; the answers already have the +/- sign, so you don't have to double it because the +/- is already accounted for. Make sense?
    Wrong, read my post to see why
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    (Original post by bhowland1994)
    Wrong, read my post to see why
    How can I be wrong when I would get the right answers whilst you wouldn't ?


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    (Original post by James A)
    Water doesn't act as a nucleophile, but the OH breaks off the water, which uses it's lone pair to attack the delta positive carbon. (this is what displaces the halide)
    Water acts as the nucleophile... The hydrogen breaks off as the water attacks not before


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    (Original post by Goods)
    It depends on whether you are adding an acid or an alkali


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    yes exactly didn't read what it said in tiny characters on the right, Thanks!
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    Really panicking now barely know any of the group 7 reactions

    ... like how to make H3PO3. It's just too much !!

    And the only two indicators we need to know about is:

    Phenolphthalein
    acid - colourless
    neutral - pale pink
    alkali - purple

    Methyl orange
    acid - red
    neautral - orange
    alkali - yellow


    Is this correct ? Thanks!
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    (Original post by bhowland1994)
    Wrong, read my post to see why
    25cm3, which could be 0.06cm3 out i.e. 0.06 above or 0.06 below, which is a total of 0.12cm3

    0.12/25=0.48% and this is the total percentage error, which is what Matterhorn is asking.

    In answer to the original question, it is +/-0.24% because the plus or minus is already accounted for.
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    (Original post by Linked)
    Can anyone answer part b for me with an explanation please?
    please
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