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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by Matterhorn)
    Attachment 222980

    Why don't you doubt the 0.06 seeing as it is plus or minus?

    Answer is c
    Rookie error, you have multiplied your uncertainty by two .... Why?, your using a pipette not a burette :P
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    Why is ethanol a polar molecule.
    and why is propane a non polar molecule?
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    (Original post by James A)
    They don't even form H bonds at all. Fluoroalkanes cannot hydrogen bond.
    Oh ya, the electronegativity difference between F and C is not high enough to make Fluorine sufficiently delta-.
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    h
    (Original post by posthumus)
    Heat under Reflux apparatus

    oh okay



    At most you'll just need to know this really:

    The liberated iodine reacts with thiosulfate ion (after adding KI to your solution being tested)

    I2 + 2S2O3^2- ----> 2I- + S4O6^2-

    They give you this stuff anyway usually, it's calculations you should be most concerned with
    oh okay , what abt how to prepare ki
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    (Original post by posthumus)
    Hey goods could you explain to me why beryllium is so unreactive ? [possibly with reference to BeO layer]

    also any observations to be made about the group 2 oxides, are they white too solids too ?
    Beryllium is very reactive but it forms strong insoluble oxides and hydroxides that form a layer that prevents further reaction.

    Just make generic observations like solid sodium melts and disappears gas/effervescence/fizzing

    Melt burns and a white powder is formed


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    Heading off now :P
    Good luck everyone!! Do your best, all will be fine
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    (Original post by Mimi85)
    h
    oh okay , what abt how to prepare ki
    Heat potassium with iodine


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    (Original post by Hi, How are you ?)
    Why is ethanol a polar molecule.
    and why is propane a non polar molecule?
    Anyone ?
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    (Original post by Hi, How are you ?)
    Why is ethanol a polar molecule.
    and why is propane a non polar molecule?
    Ethanol has polar bond and is non symmetrical hence net polar

    Propane is symmetrical and so any tiny dipoles in c-h bonds cancel out hence non polar


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    (Original post by Mimi85)
    h
    oh okay , what abt how to prepare ki
    It's a reagent, you don't need to know how to prepared it.

    (Original post by Goods)
    Beryllium is very reactive but it forms strong insoluble oxides and hydroxides that form a layer that prevents further reaction.

    Just make generic observations like solid sodium melts and disappears gas/effervescence/fizzing

    Melt burns and a white powder is formed


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    Oh okay thanks I guess you meant unreactive there.... so group 2 oxides are all white

    therefore when group 2 nitrates decompose you can observe white precipitates + brown fumes ?
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    Why are Chlorine free radicals and nitrogen monoxides and dioxides described as catalyst, (I know they speed up the depletion of the ozone layer, but why though). Tanks =)
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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?
    Yeah thanks I didn't see that!


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    (Original post by bhowland1994)
    Rookie error, you have multiplied your uncertainty by two .... Why?, your using a pipette not a burette :P
    Cause it was plus or minus so I thought double it as it can go either way but as I was shown, the answers take the plus or minus into account


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    (Original post by Hi, How are you ?)
    Why are Chlorine free radicals and nitrogen monoxides and dioxides described as catalyst, (I know they speed up the depletion of the ozone layer, but why though). Tanks =)
    Because they react , and then the free radical is regenerated in further reactions.

    They speed up the depletion because one free radical can result in the formation of thousands of free radicals, and each of those can form more free radicals etc.
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    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)
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    (Original post by posthumus)
    It's a reagent, you don't need to know how to prepared it.



    Oh okay thanks I guess you meant unreactive there.... so group 2 oxides are all white

    therefore when group 2 nitrates decompose you can observe white precipitates + brown fumes ?
    Beryllium metal is very reactive but it reacts to form very stable insoluble compounds(oxides hydroxides) that form a layer that prevents further reaction hence the reactions stop.

    Group 2 and lithium give off no2 and O2
    No2 is brown so you can compare thermal stability by comparisons the times until brown gas is produced. The nitrate is already white so you can observe a change. Just say it also produces a gas that relights a glowing splint(O2)


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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)
    It's insignificant


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    (Original post by Matterhorn)
    Cause it was plus or minus so I thought double it as it can go either way but as I was shown, the answers take the plus or minus into account


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    No, the reason we double is because we are taking two readings from the same piece of equipment, therefore are uncertatinity in the overall reading doubles. The +/- are just there to represent the fact that your actual value can be either side of the predicted value
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    (Original post by Gnome :))
    Because they react , and then the free radical is regenerated in further reactions.

    They speed up the depletion because one free radical can result in the formation of thousands of free radicals, and each of those can form more free radicals etc.
    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*?
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    (Original post by bhowland1994)
    No, the reason we double is because we are taking two readings from the same piece of equipment, therefore are uncertatinity in the overall reading doubles. The +/- are just there to represent the fact that your actual value can be either side of the predicted value
    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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