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

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    (Original post by CoolRunner)
    1 mark? I think.
    yehh 1
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    What everyone say for the question on why there's a smaller peak at m/z 20? I threw in molecular fragmentation of water, is this right?

    Water Mr=18, so it makes sense to get peaks below18 which are smaller, but HOW do you get peaks above 18?
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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.
    Yeah, I also put this.

    I saw fragmentation in one of the past papers, so we should be fine
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    i said fragmentation as well
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    (Original post by emicroteen96)
    i said fragmentation as well

    (Original post by DomGunstone)
    Yeah, I also put this.

    I saw fragmentation in one of the past papers, so we should be fine
    Water Mr=18, so it makes sense to get peaks below18 which are smaller, but HOW do you get peaks above 18?
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    (Original post by krisshP)
    1 HF-->50%-->6000 years
    2HF-->25%-->12,000 years
    3HF-->12.5%-->18,000 years

    They told you the HF was 6000 years
    Oh fugggerr!! I did 12000 x 2 instead of 12000 add 6000 ffss lol stupid mistake
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    Makes no sense to get peaks above 18
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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?
    If u use an isotope of O with a mass off 18, it would add up to 20 including the hydrogen atoms in the water molecule
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    youre right the highest one is usually the compound, but its 18 not 20
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    (Original post by Ikklemini)
    If u use an isotope of O with a mass off 18, it would add up to 20 including the hydrogen atoms in the water molecule
    So then fragmentation of water is wrong right?
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    How many UMS is this paper out of?
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    (Original post by krisshP)
    So then fragmentation of water is wrong right?
    It's right.

    You could just say that 2 or more electrons have been removed from the outer shell/s as an alternative answer.
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    For the one where we had to write an ion, was it 18/6 O (-2)?
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    (Original post by nukethemaly)
    How many UMS is this paper out of?
    90 UMS
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    (Original post by DomGunstone)
    It's right.

    You could just say that 2 or more electrons have been removed from the outer shell/s as an alternative answer.
    No you can't since then the charge would be say +2 nd m/z where z=+2 would mean a lower peak, not a greater peak at m/z 20 they were asking for
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    How do you convert results to UMS?


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    (Original post by krisshP)
    So then fragmentation of water is wrong right?
    Fragmentation would have a m/z lower than 20 and it said in thhe question many isotopes of oxygen with the MAIN one being 16-O
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    (Original post by krisshP)
    One question was about writing a reaction. It was worth only 1 mark and it did NOT mention anything on state symbols. I wrote the reaction, but didn't put state symbols since I was a bit unsure with what the state symbols would be or that reaction and I didn't want to risk showing incorrect state symbols. Is this okay?
    There was only one where it asked about state symbols, lets just hope the one you're describing isnt it. :P
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    (Original post by SyedaK)
    How do you convert results to UMS?


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    http://www.ocr.org.uk/i-want-to/do/c...eting-results/
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    (Original post by madrevision)
    what error, i got the ion question wrong- on the back page
    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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