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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by Gnome :))
    The ClO* can then react with O2 to make Cl* and O3.

    Or it could react with O* to form O2 and Cl*
    But you always have 1 free radical, so how does it make more free radicals?
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    (Original post by Hi, How are you ?)
    But you always have 1 free radical, so how does it make more free radicals?
    it doesn't, the same one is just regenerated.
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    Guys do we need to know any apparatus for experiments? Like how to set-up an experiment with labelled diagrams? If so, please explain what we need to know! Thanks!
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    (Original post by Hi, How are you ?)
    But you always have 1 free radical, so how does it make more free radicals?
    The free radical is regenerated, but this regenerated free radical can then attack more ozone.
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    (Original post by Gnome :))
    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.
    No, your not understanding. Think about it this way, your taking one reading, so you cant have the two worst extremes 25.06 and 24.94, its either one or the other
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    (Original post by posthumus)
    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!
    Phelophthalein is pink in alkali, don't say purple, i've seen 'reject purple' in a mark scheme before
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    (Original post by GCSE-help)
    Phelophthalein is pink in alkali, don't say purple, i've seen 'reject purple' in a mark scheme before
    Okay thanks ! Damn george facer !!!!!!!

    So

    Acid - colourless
    neutral - pale pink
    alkali - pink

    Is this correct now ??
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    can anyone explain what Sn1 and Sn2 mechanisms are?
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    (Original post by posthumus)
    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!
    Are you sure we need to know how to make phosphoric acid?
    And yes you are right but mark scheme says red for alkali phenolphthalein


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    (Original post by upthegunners)
    it doesn't, the same one is just regenerated.
    So no new free radicals are made, it is just formed once again, and I am presuming that this process is fast, right.

    So since it forms a chain reaction, it keeps the reaction going until there is a terminating step?
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    (Original post by Hi, How are you ?)
    So no new free radicals are made, it is just formed once again, and I am presuming that this process is fast, right.

    So since it forms a chain reaction, it keeps the reaction going until there is a terminating step?
    yep that's exactly it
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    (Original post by Matterhorn)
    Are you sure we need to know how to make phosphoric acid?
    And yes you are right but mark scheme says red for alkali phenolphthalein

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    Thanks ! I Really hope not I barely know any group 7 reactions... Even the ClO- stuff.
    I'm going to flick through the paper for about 2 minutes, get all the equations or "memorizing stuff" out of the way.
    If there aren't any, then I can stay relaxed for the rest of the exam

    (Original post by Linked)
    can anyone explain what Sn1 and Sn2 mechanisms are?
    (Original post by posthumus)
    Yh sure
    S - substitution
    N - nucleophile
    'no.' - how many species involved in first step

    Well usually associate the Sn2 mechanism with primary halogenoalkanes (for this particular unit anyway).
    2 species are involved in the initial step... the nucleophile & the halogenoalkane. The delta - element in the nucleophile moves towards the delta + carbon in the halogenoalkane.
    While it does this, The C-Br is in the process of breaking (electrons given to bromine).
    So a bond is forming & breaking at the same time... this is called the transition state.
    Here I've found an example of Sn2 reaction (ignore equilibria signs):
    Moving onto Sn1 ...

    In tertiary halogenoalkanes.... there are 3 methyl groups, these pushed electrons towards the carbon atom and make it less delta positive. This makes the C-X bond weak therefore it break. No nucleophile is required to approach it. The first step only contains one species... the halogenoalkane, hence the one in Sn1.
    Here's an example of an Sn1 mechanism:


    (Nu = nucleophile)

    Mechanisms for secondary alcohols never comes up I believe... but they can undergo both Sn1 & Sn2. Though Sn1 is the most likely mechanism.

    Hope that helps
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    Anyone know if we will ever get asked to calculate solubility?
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    (Original post by Masturchess)
    Anyone know if we will ever get asked to calculate solubility?
    would highly doubt it, but how longs it guna take to look over it in case it did?

    Be safe.
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    (Original post by upthegunners)
    would highly doubt it, but how longs it guna take to look over it in case it did?

    Be safe.
    How do even calculate solubility?
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    (Original post by upthegunners)
    yep that's exactly it
    So is the free radical substitution a fast reaction then?
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    We have to wait till tomorrow to discuss it right?


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    (Original post by Masturchess)
    Anyone know if we will ever get asked to calculate solubility?
    Here's your answer:

    (Original post by Hi, How are you ?)
    How do even calculate solubility?
    (Original post by GCSE-help)
    Phelophthalein is pink in alkali, don't say purple, i've seen 'reject purple' in a mark scheme before


    It's colourless in acid, pink in neutral conditions and red in alkali.
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    (Original post by Big-Daddy)

    It's colourless in acid, pink in neutral conditions and red in alkali.
    And pink at the end-point !

    Great thanks... now I just need to remember the name
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    Hasn't anyone done the exam already in Eastern Europe or further East?
 
 
 
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