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

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    It was, .2/84 =y
    Y= co2 mole
    Y x24 x1000

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    (Original post by tasniaa)
    jihadbexdnw feih
    3 marks down the drain.

    I think I've got 48/60
    Don't think that'll be good enough for an A
    Damn :'(
    An A is normally 48, this was easier so maybe 50
    Plus grades don't matter at this stage

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    (Original post by Ikklemini)
    Urm I wrote about using limewater and testing the time it takes for it to go milky, the longer time the higher the thermal stability- bot sure if thats what they asked for- also said Sr is more thermally stable than Mg as thermal stability of Carbonates increases down group 2

    What did everyone else write ?
    yh that's right but I got confused because before the exam I read something where it was Ca and Mg so I ended up writing it would take longer for the Ca solution to turn cloudy, but I got everything else so I should get about 2/4
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    (Original post by CoolRunner)
    I got 18.000 for number of years about the half life question

    I also got 56.9 for the volume in cm3
    How did you calculate the half life?
    I did 6000 * 0.875 to give 5250 years
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    (Original post by TheNote)
    How did you calculate the half life?
    I did 6000 * 0.875 to give 5250 years which fits for the ice age stuff they talked about.
    You divide 100 by 2 = 50
    /2 = 25
    /2 = 12.5

    Since it has halved 3 times, there have been 3 half lives. 3 x 6000 = 18,000
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    (Original post by TheNote)
    How did you calculate the half life?
    I did 6000 * 0.875 to give 5250 years

    As in the question it said they found 12.5% remaining and the half life is 6000 years.

    I did 100% to 50% is 6000 years
    50% to 25% is 6000 years
    25% to 12.5% is 6000 years

    3 amounts of 6000 years had gone by so 18,000 years, as it is decay you start with the full amount, halve that, then halve that etc.
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    For the gas question, I left it as 56.88 as it didn't specify a certain amount of significant figures, will I get marked down..
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    (Original post by Ikklemini)
    Hey what did everyone get for the years from the half life question? I got something like 26000 years ?!
    1 HF-->50%-->6000 years
    2HF-->25%-->12,000 years
    3HF-->12.5%-->18,000 years

    They told you the HF was 6000 years
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    (Original post by Izzy_saul)
    For the gas question, I left it as 56.88 as it didn't specify a certain amount of significant figures, will I get marked down..
    I think it should be fine 2dp is not an unreasonable degree of accuracy
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    What did everyone put for the neutralisation question and how it does more neutralisation?
    I said it's got and extra OH-
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    (Original post by krisshP)
    What did everyone put for the neutralisation question and how it does more neutralisation?
    I said it's got and extra OH-
    yh I put it's got more OH- ions, these are electron donors lol
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    What everyone say foe the question on why there's a smaller peak at m/z 20?
    I threw in molecular fragmentation of water.
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    (Original post by anthonyrf)
    I calculated the Mr of MgCO3 which was 84.3 I think.

    The question told you that we had 0.2g of MgCO3 so the no. Moles of MgCO3 was 0.2/84.3 = 0.00237247...

    ratio of CO2 to MgCO3 was 1:1 so moles of CO2 = 0.00237247...

    therefore Vol. of CO2 in cm3 was 0.00237247... x 24000 which = 56.94 (2dp)
    Yay that's what I did
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    Wait say if in the calculation for CO2 volume in cm3 I used accurate values ie fraction for the moles of CO2/magnesium carbonate, but I did round my final answer to 3SF and was right, would I get full marks for the question?

    Thanks
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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.
    I thought that the question there was about oxygen... did I read it wrong? x.x Oh no! I get it now. Looks like that's another mark that I lost... I assume that it was an ion where the oxygen had an atomic mass of 18.
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    Any news of an unnofficial mark scheme??
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    Oh no, I said for the one on the last page)
    H2O+
    and 'Water contains an isotope of water which has a mass of 16'
    ugh
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    I'm such an idiot.

    For the approximation/assuming enthaply change question i written this, will i got 2 marks?

    1) Hcl has the same density as 1gcm-1 (SAME AS WATER)
    2) Hcl has a specific heat capacity as 4.18gj-1k-1 (same as water)

    do i get the marks, even though my values are stupidly wrong (i did put brackets to say it is the same as water for both)
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    how many marks was the half life question and the table with CO2 and Sio2 and diamond
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    (Original post by emicroteen96)
    how many marks was the half life question and the table with CO2 and Sio2 and diamond
    1 mark? I think.
 
 
 
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