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Edexcel - Chemistry Unit 2 - 4 June 2013 Watch

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    (Original post by sophiekutie)
    What!?!! I though magnesium was definitely white!
    I think as a solid it is white but in a flame test it is like "No Colour Visible" which is from a markscheme
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    does anyone know what the answer was to the carbon neutral MC question, about which factor wasn't necessary in assessing a fuel?
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    (Original post by jollygood)
    But why did they ask that what would be colour change in absence of starch indicator? there must be something different about it.
    Starch is blue-black to colourless, iodine is brown/yellow to colourless. That's a difference!
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    For the MgCO3 and BaCO3 question, I think you needed to use the test including lime water to see how fast the limewater turns from colourless to 'milky' colour due to the presence of CO2
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    (Original post by wildyoungheartsx)
    does anyone know what the answer was to the carbon neutral MC question, about which factor wasn't necessary in assessing a fuel?
    I think the one that said amount of energy released on burning one tone of biofuel was correct. because carbon neutrality is concerned with amount of carbon dioxide absorbed and released not with energy. the other three options all included the burning of fuels to process fertilizers or to run machinery.
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    [QUOTE=jollygood;42994902]What I did for MgCO3 and BaCO3 question in first part I wrote the equation and said that on giving the same amount of heat to both carbonates, Mg carbonate lump will break and bubbles of gas can be seen rising if u do it properly like collecting gas above water. but on providing same amount of heat there will be no gas produced. and u can check it b y lime water. I just wrote it to be on safe side. In the next part without HEATING one I said the TEST WITH LIME WATER. and said as a continuation of first part that the gas collected already can turn lime water milky in case of magnesium carbonate but not in case of barium carbonate.[/QUOTE
    i put the flame test for the first part because it said it was a powder. for the second part i talked about thermal decomposition and how magnesium forms an oxide and turns limewater cloudy quick than baruim
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    (Original post by Jayqwe)
    For the MgCO3 and BaCO3 question, I think you needed to use the test including lime water to see how fast the limewater turns from colourless to 'milky' colour due to the presence of CO2
    That's what I put for the first part and the second part not using heat or acid I said it's solubility in water.
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    (Original post by Jayqwe)
    For the MgCO3 and BaCO3 question, I think you needed to use the test including lime water to see how fast the limewater turns from colourless to 'milky' colour due to the presence of CO2
    yeah that's what i talked about and also i talked about the oxide forming quicker for magnesuim
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    The main thing im stressing over is drawing an Sn2 mechanism instead of Sn1. It was a secondary haloalkane, and nearly all books say both are possible and at first I thought the MS would accept both mechanisms, but people seem to be convinced only sn1 is appropriate?
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    (Original post by GCSE-help)
    The main thing im stressing over is drawing an Sn2 mechanism instead of Sn1. It was a secondary haloalkane, and nearly all books say both are possible and at first I thought the MS would accept both mechanisms, but people seem to be convinced only sn1 is appropriate?
    I just drew a standard nucleophillic substitution reaction haha, Unit 2 doesnt focus much on sn1 or sn2 and shouldn't do because it's a unit 4 thing
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    (Original post by Kurraiyo)
    According to the previous mark schemes thats fine In equations there's always "Accept multiples"
    Lol thank god for that thanks


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    Anyone prediction for a C grade would be? LOL I'm serious
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    How many marks was the magnesium catbonate test question 2 or 3??
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    (Original post by GCSE-help)
    The main thing im stressing over is drawing an Sn2 mechanism instead of Sn1. It was a secondary haloalkane, and nearly all books say both are possible and at first I thought the MS would accept both mechanisms, but people seem to be convinced only sn1 is appropriate?
    Seriously, don't stress. My friends and I all put Sn2. It said "suggest an appropriate mechanism" - my guess is they'll accept both as it's secondary and it's not definite that secondary halogenoalkane would go by Sn1.
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    Does Sn2 use curly arrows with a pair of electrons? If not, then Sn2 is wrong.

    Although I did do Sn1 to play it safe.
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    (Original post by jollygood)
    I think the one that said amount of energy released on burning one tone of biofuel was correct. because carbon neutrality is concerned with amount of carbon dioxide absorbed and released not with energy. the other three options all included the burning of fuels to process fertilizers or to run machinery.
    Same! I did this too!
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    (Original post by James A)
    Does Sn2 use curly arrows with a pair of electrons? If not, then Sn2 is wrong.

    Although I did do Sn1 to play it safe.
    Yeah Sn2 and Sn1 both use curly arrows with pair of electrons, because at the end of the day they're both nucleophillic mechanisms and the main point of a nucleophile is a lone pair of electrons attacking an electron deficient sight.

    Hopefully both mechanisms are accepted
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    (Original post by TheBigGeek)
    Seriously, don't stress. My friends and I all put Sn2. It said "suggest an appropriate mechanism" - my guess is they'll accept both as it's secondary and it's not definite that secondary halogenoalkane would go by Sn1.
    Thanks
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    (Original post by kevsamuel)
    oh well, thanks anyway how many marks was that question? just one right?
    Yeah probably only one, dont sweat over it.
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    For all this Sn1 ans Sn2 business surely the answer for suggest a mechanism was neucleophilic substitution and you wouldn't have to specify Sn1 or Sn2. I make this assumption because we have to bare in mind that this was a paper aimed at year 12's and the Sn1 and Sn2 is a year 13 thing. Which leads me to believe that a fair few of you are in my position which is people who are resitting and are in year 13, hence you mentioning Sn1 and Sn2 which may have been over complicating the question. Also us year 13's dont even know how to decide weather a secondary will undergo Sn1 or Sn2 so I doubt they would expect a year 12 to know. I'm not saying I'm right but that's just my thought on the matter.
 
 
 
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