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Edexcel - Chemistry Unit 2 - 4 June 2013 watch

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    (Original post by ALevel96)
    Did everyone times precentage error by two?
    Nope I left mine as it was :eek:
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    (Original post by GCSE-help)
    Nope I left mine as it was :eek:
    Ahh! It said two readings occur what is the mean titre
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    (Original post by James A)
    For the halogenoalkane with NaOH condition (the second one), I said that it has to be heated under reflux.

    But for the elimination condition, I said that it must be dissolved in ethanol. It didn't cross my mind to put 'dissolved in water' for the NaOH (the second condition question below the elimination one). But then again, aren't we assuming that dilute NaOH is dissolved in water?
    I don't remember, man. The very last question put so much stress on me that I couldn't finish it.

    "Why the heck are the scientists more worried about CO2 acting as greenhouse gas than water vapor?"
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    Percentage error sorry what am I on about haha
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    (Original post by ALevel96)
    Did everyone times precentage error by two?
    Ya, it will be times 2 as you take the burette reading twice.
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    That paper was strange, Sections A and C were easy except but the first question of section B set me back a minute as I just couldn't remember the formula and then I was getting so stressed but luckily I think you had to react with 2H2O hopefully and I messed up on the parts per million question. Also did anyone notice that there were loads of one markers and the drawing of the mechanism was 2 and the highest was probably 4 marks which was the greenhouse gas written question right at the end.

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    (Original post by airheadbuster)
    I don't remember, man. The very last question put so much stress on me that I couldn't finish it.

    "Why the heck are the scientists more worried about CO2 acting as greenhouse gas than water vapor?"
    The question asked for reasons why the scientists are concerned more about CO2.

    I said.

    CO2 levels can be controlled to a certain extent, water vapour concentration cannot be controlled.

    The actions of humans increases the CO2 concentration, because it acts as a greenhouse gas, which traps heat energy, therefore polar ice caps melt and a rise in sea level is observed. Also I mentioned about deforestation which increase CO2 concentration and the excess burning of fuels (which produce CO2 on combustion).
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    (Original post by Jayqwe)
    That paper was strange, Sections A and C were easy except but the first question of section B set me back a minute as I just couldn't remember the formula and then I was getting so stressed but luckily I think you had to react with 2H2O hopefully and I messed up on the parts per million question. Also did anyone notice that there were loads of one markers and the drawing of the mechanism was 2 and the highest was probably 4 marks which was the greenhouse gas written question right at the end.

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    It was sn1
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    Did we need to show the transition states? It was only 2 marks


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    (Original post by Goods)
    It was sn1
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    I think they'll accept both, as it's secondary, but it's better to go with the safe option!
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    (Original post by Tuya)
    Did we need to show the transition states? It was only 2 marks


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    You had to show the full mechanism.
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    For the titration what did you guys put to improve it?
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    Any ideas on what the full ums boundary is?


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    (Original post by ALevel96)
    For the titration what did you guys put to improve it?
    Increase volume of I2. So, the volume of thiosulfate needed to neutralise it will be more. Therefore, the percentage uncertainty will decrease.
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    Well I put use a smaller concentration which results in a larger titre and smaller % error
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    (Original post by James A)
    The question asked for reasons why the scientists are concerned more about CO2.

    I said.

    CO2 levels can be controlled to a certain extent, water vapour concentration cannot be controlled.

    The actions of humans increases the CO2 concentration, because it acts as a greenhouse gas, which traps heat energy, therefore polar ice caps melt and a rise in sea level is observed. Also I mentioned about deforestation which increase CO2 concentration and the excess burning of fuels (which produce CO2 on combustion).
    Your answer is almost spot on. Mine... :mad: (I thought combustion also produces steam whereas most of the time water is produced)
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    (Original post by Goods)
    It was sn1
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    Really? Thats cool, I wasn't sure for a minute but since it was the only mechanism I did sn1 just in case, btw did we have to say it i Sn1 or is it implied with the drawing?

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    (Original post by ALevel96)
    Well I put use a smaller concentration which results in a larger titre and smaller % error
    Your answer seems correct. Not sure though. Not sure about mine either.
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    (Original post by ALevel96)
    For the titration what did you guys put to improve it?
    I said that we should split the excess iodine (that we had to titrate) into seperate beakers, so more titrations can be carried out, hence a mean titre can be obtained.
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    (Original post by ALevel96)
    Well I put use a smaller concentration which results in a larger titre and smaller % error
    All that will do is increase the accuracy of the experiment, not the reliability.

    To get a more reliable titre, you need to carry out more than one titration. Only the one titration was carried out in the question.
 
 
 
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