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    Oh, right. I did factor in the mass of the water. But i got 35.75%
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    (Original post by Daxx)
    Yeah last question on the Transition Metals paper.







    On the Trends Paper, the question just after the enthalpy one:

    Was the purity of [some compound with 7H2O] around 75 76 or 77.8%

    can't remember what I put.

    you had to factor in the mass of the water.

    Yep it was 76.7% or there abouts i can't really remember but we must have got same thing!
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    (Original post by jseldis)
    Oh, right. I did factor in the mass of the water. But i got 35.75%
    Yeah like half people have done
    I did that and it makes much more sense but hey we aint marking it hehe
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    i did that triangle and i got -339 but oh well probably dropped 1 mark for sign error anyways :p: only need 60 out of 90 so no big to me
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    (Original post by Gaara.)
    Yeah like half people have done
    I did that and it makes much more sense but hey we aint marking it hehe
    Oh, haha I thought like 1 person had it other than me. I think it makes alot more sense, seeing as water counts as an impurity...
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    (Original post by jseldis)
    Oh, haha I thought like 1 person had it other than me. I think it makes alot more sense, seeing as water counts as an impurity...
    You could be right there- not sure whether we will ever know unless someone gets there paper back! It was a bit of an ambiguous question, but most people i spoke to seemed to think that the water was not an impurity. You've got me worried now!
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    Yeah, it's odd question. But yeah. Why would you discount water from it? That's like putting the Mr, but taking away 35.5 because there might be some chlorine in there.
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    Oh people discounted the water to get 76%.
    Well that seems to me like its very wrong hehe, but we will wait and see
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    (Original post by atoms4peace)
    what what what?
    i dont remember that question? was this on trends and patterns?
    yeh it was trends patterns paper i think lol i forgetting exam already. you had to work out E cell by working out overall reaction
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    I did Trends and patters, and there was nothing on cells.
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    no cells on this paper
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    no, I included water and got a percentage purity of 76% or something. You ARE supposed to include the mass of water.

    i know that for a fact.
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    I know. But i got 35.75 somehting like that. How did you get 76%?
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    Doesn't it ask for the purity of the compound rather than just Iron? I got 77/76 or something.

    Btw i hope you people who have exothermic thermal decompositions do those experiments behind very strong walls because exothermic decompositions have another name, explosions. You put a lot of energy in and a lot is given out very quickly = boom.
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    Can anyone remember the figures for this percentage question? Its driving me mad, I can't remember any of it or what I put as an answer.
    You were given mass of FeSO4.7H2O, which was 2.6 - 2.8 ish I think, and a volume of sulphur dioxide produced, which was 19.6cm^3 ish I think, and there was the equation somewhere above which showed it was a 1 : 2 ratio, 1 SO2 to 2FeSO4. If anyone can remember the figures I'm sure someone can get the right method. Something like
    19.6/(1000*24) for the moles of sulphur dioxide gas
    Double it for the moles of iron sulphate
    The moles of iron sulphate are equvalent to the moles of crystallised iron sulphate (with the water bits, I'm pretty sure thats crystallised)
    And finally times that by the Mr of the whole lot.
    And yes, water should be included because it has a mass, so it affects the overall mass of the crystals, which affects the purity. I think the question asked for the purity of the FeSO4.7H2O, you would exclude water if it asked for the purity of FeSO4 because it could be treated like an impurity in that case.

    So, figures anyone?
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    Why did you have to double it? I wrote a reaction and there was nothing about doubline there.
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    Wasn't this question just 3marks?
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    Yes
    But that's 3/45
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    (Original post by jseldis)
    Yes
    But that's 3/45
    I can't imagine anyone not working out the moles of each, so your looking at 1mark lost maybe with a wrong %
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    No ya had to do the moles, but not multiply by two.
 
 
 
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