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OCR B (Salters) Chemistry F331 (Chemistry for Life) Thursday 23rd May Exam Discussion Watch

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    For the last few questions I said the peaks show the abundance of the ions, h20+ and then wrote about oxygen having an isotope of mass 18, which would make a h20 ion with mass 20, any ideas whether any of this is wrong?
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    (Original post by jehearo)
    At first I didn't notice that they were talking about water but then four minutes to the end I finally noticed and quickly wrote down the right answer *phew*


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    The answer was [H2O]+ right?
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    (Original post by SyedaK)
    How do you convert results to UMS?


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    You need the grade boundaries for example for the june 2012 paper here it says 49/60 is 72UMS http://www.ocr.org.uk/Images/16472-u...-june-2012.pdf
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    (Original post by hhustad)
    Yeah I wrote that too. I changed my answer at least 4 times though. I put (h2o)2+


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    It would be H2O + since m/z is 18 - this means there must be a 1+ charge since the Mr of water is 18



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    (Original post by RevisionEssence)
    The answer was [H2O]+ right?
    Yep


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    (Original post by jehearo)
    At first I didn't notice that they were talking about water but then four minutes to the end I finally noticed and quickly wrote down the right answer *phew*


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    oh I didn't even know fully till now :/ , I just knew I got it wrong but I wasn't sure why
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    (Original post by krisshP)
    Water Mr=18, so it makes sense to get peaks below18 which are smaller, but HOW do you get peaks above 18?
    Fragmentation would result in a smaller m/z - you would have to mention that there could be heavier isotopes of oxygen.


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    (Original post by DomGunstone)
    90 UMS
    unit 2 is 150?
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    Thank you


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    (Original post by nukethemaly)
    unit 2 is 150?
    Yep, I think so.
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    Well, I'm sure that I've lost at least 7 marks, probably more... just stupid mistakes. >.< There goes my chance of 90% UMS... the grade boundaries for this one could mean that I don't even get an A...
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    (Original post by Hamster96)
    How can so many people complain about missing the last page. They weren't trying to catch anyone out, they even wrote in bold letters "QUESTION 4 CONTINUES ON THE NEXT PAGE". You can't blame the exam board, you just need to read what's on the paper. Sorry if this offends anyone that missed it, but I don't see how it's anyone's fault but your own if you forget to read something, no point complaining about it now, what's done is done, and chances are those 3 marks won't affect your grade by much anyway.
    Only thing I'm hoping is that (not to be mean) a lot of people missed them so the boundaries will be lower
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    Yay, think I lost about 3~4 marks to be safe, in case examiners don't like how I worded my answers. The questions I found awkward I got right for some reason.
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    (Original post by JamesMartinez)
    Only thing I'm hoping is that (not to be mean) a lot of people missed them so the boundaries will be lower
    Hahaha, I agree.
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    (Original post by yl95)
    Yay, think I lost about 3~4 marks to be safe, in case examiners don't like how I worded my answers. The questions I found awkward I got right for some reason.
    Yeah. How did you find the calculations?

    I usually find them more difficult, but I got them both correct this time; I don't know what's wrong with me...
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    (Original post by JamesMartinez)
    Only thing I'm hoping is that (not to be mean) a lot of people missed them so the boundaries will be lower
    Yep, I agree. Paper was very easy so that could help us out in getting a higher grade
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    Is there a mark scheme up anywhere for this exam?

    I think it was pretty similar to any of the other past papers, got the last bit wrong but knew that as I wrote my answer down...
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    (Original post by jehearo)
    Fragmentation would result in a smaller m/z - you would have to mention that there could be heavier isotopes of oxygen.


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    NOOOOOOOO

    was that question just one mark?
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    (Original post by krisshP)
    What everyone say foe the question on why there's a smaller peak at m/z 20?
    I threw in molecular fragmentation of water.
    2 hydrogens bonded to the isotope of oxygen with Mr 18.
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    What did everyone say for the question where we were asked to say 2 things we'd observe when calcium mixes with water or whatever the question was?
 
 
 
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